Controlling both ground- and excited-state thermal barriers to Bergman cyclization with alkyne termini substitution

The cross-coupling reaction of 2,3-dibromo-5,10,15,20-tetraphenylporphyrin with corresponding organostannanes in the presence of a Pd0 catalyst in THF at reflux temperature yields free base 2,3-dialkynylporphyrins 1a,c-e. The subsequent deprotection of trimethylsilyl group of 1a with TBAF in THF under aqueous conditions produces the 2,3-diethynyl-5,10,15,20-tetraphenylporphyrins 1b in 87% yield. Compounds 1a-d undergo zinc insertion upon treatment with Zn(OAc)2.2H2O in CHCl3/MeOH to give zinc(II) 2,3-dialkynyl-5,10,15,20-tetraphenylporphyrins (2a-d) in 70-92% yields. Thermal Bergman cyclization of 1a-e and 2a-d was studied in chlorobenzene and approximately 35-fold 1,4-cyclohexadiene at 120-210 degrees C. Compounds 1b and 2b with R = H react at lower temperature (120 degrees C) and produce cyclized products 3b and 4b in higher yields (65-70%) than their propyl, isopropyl, and phenyl analogues, with R = Ph being the most stable. Continuing in this trend, the -TMS derivatives 1a and 2a exhibit no reactivity even after heating at 190 degrees C in chlorobenzene/CHD for 24 h. Photolysis (at lambda >/= 395 nm) of 1b and 2b at 10 degrees C leads the formation of isolable picenoporphyrin products in 15 and 35% yields, respectively, in 72 h, whereas these compounds are stable in solution under same reaction conditions at 25 degrees C in the dark. Unlike thermolysis at 125 degrees C, which did not yield Bergman cyclized product for R = Ph, photolysis generated very small amounts of picenoporphyrin products (3c: 5%; 4c: 8% based on 1H NMR) as well as a mixture of reduced porphyrin products that were not separable. Thus, trends in the barrier to Bergman cyclization in the excited state exhibit the same trend as those observed in the ground state as a function of R-group. Finally, photolysis of 2b at 10 degrees C with lambda >/= 515 or 590 nm in benzene/iPrOH (4:1, 72 h) produces 4b in 15 and 6% isolated yields, indicating that conjugation of the enediyne unit into the porphyrin electronic transitions leads to sufficient distortion to generate photoproduct even with long wavelength excitation.     

Intramolecular Pauson-Khand reactions of methylenecyclopropane and bicyclopropylidene derivatives as an approach to spiro(cyclopropanebicyclo[n.3.0]alkenones)

The trimethylsilyl-protected enynes 9a-c and 14a,b with alkynyl substituents on the three-membered ring or on the double bond of a methylenecyclopropane or a bicyclopropylidene moiety were prepared in two steps from the alcohols 6a-c and 12a,b, respectively, by conversion to the iodides and their coupling with lithium (trimethylsilyl)acetylide (8) in 38-73% overall yields. The bicyclopropylidene derivative 9d was synthesized in 49% yield directly from bicyclopropylidene (3) by lithiation followed by coupling with (5-iodopent-1-ynyl)trimethylsilane (11). Enynes 9b-d were protiodesilylated by treatment with K2CO3 in methanol to give the corresponding unprotected enynes 10b-d in 53, 74 and 94% yield, respectively. Enynes 17a-c with a carbonyl group adjacent to the acetylenic moiety were synthesized from oxo derivatives 15a-c by Wittig olefination followed by coupling with 8 in 47, 18 and 12% overall yield, respectively. Pauson-Khand reactions of the methylenecyclopropane derivatives with a substituent on the ring (9a,b and 10a) as well as on the double bond (14a,b and their in situ prepared protiodesilylated analogues) proceeded smoothly by stirring of the corresponding enyne with [Co2(CO)8] in dichloromethane at ambient temperature followed by treatment of the formed complexes with trimethylamine N-oxide under an oxygen atmosphere at -78 degrees C to give tricyclic or spirocyclopropanated bicyclic enones 18a,b, 19a, 20a,b, 21a,b in good yields. Alkynylbicyclopropylidene derivatives 9c,d and 10c,d formed the corresponding cobalt complexes at -78 to -20 degrees C. Treatment of the latter with N-methylmorpholine N-oxide under an argon atmosphere at -20 degrees C gave the spirocyclopropanated tricyclic enones 18c, 19c and 18d in 31-45% yields. The structure of 19c was proved by X-ray crystal structure analysis. The cyclization of enynones 17a-c in MeCN at 80 degrees C gave the spirocyclopropanated bicyclic diketones 22a-c in 38-65% yields. Intramolecular PKRs of the enynes 25a,d with a chiral auxiliary adjacent to the triple bond gave the corresponding products 26a,d in 70 and 79% yield, respectively, as 5:1 and 8:1 mixtures of diastereomers, respectively. Addition of lithium dimethylcuprate or higher order cuprates to the double bond of the former furnished bridgehead-substituted bicyclo[3.3.0]octanones 27a-c in 57-86% yields. Protiodesilylation of 27a followed by acetal cleavage gave the enantiomerically pure spirocyclopropanated bicyclo[3.3.0]octanedione (1R,5R)- 29a with [alpha]D(20)=-148 (c=1.0 in CHCl3) in 55% overall yield.     

Regioselective formation of beta-alkyl-alpha-phenyliridabenzenes via unsymmetrical 3-vinylcyclopropenes: probing steric and electronic influences by varying the alkyl ring substituent

The synthesis of unsymmetrical (Z)-1-alkyl-3-(2-iodovinyl)-2-phenyl-1-cyclopropenes (R=Me (8 a), Et (8 b), iPr (8 c), and tBu (8 d)) and their reactions with Vaska's complex [Ir(CO)Cl(PPh3)2] and its trimethylphosphine analogue [Ir(CO)Cl(PMe3)2] were investigated. Iridabenzvalene (13/20), iridabenzene (14/21), and/or eta(5)-cyclopentadienyliridium complexes (15/22) were obtained in modest yields and were fully characterized by spectroscopic means. X-ray structural data was secured for iridabenzvalene 13 d and iridabenzenes 14 a,b,d. Whereas iridabenzenes 14 a-c were stable at 75 degrees C for 48 h, 14 d, which possesses a bulky tBu group, rearranged cleanly to cyclopentadienyliridium 15 d at 50 degrees C over 15 h and displayed first-order kinetics. The influence of the alkyl substituent on the mechanisms of iridacycle generation, isomerization, and iridabenzene regioselectivity is discussed.     

A new protocol for a regioselective aldol condensation as an alternative convenient synthesis of beta-ketols and alpha,beta-unsaturated ketones

A general and convenient synthesis of beta-ketols and alpha,beta-alkenones has been achieved by a Knoevenagel condensation of a beta-ketoacid with an aldehyde in aqueous medium. Saponification of a beta-ketoester by an aqueous KOH 10% solution gives the potassium salt of the beta-ketoacid, which is condensed in situ with an aldehyde at pH 7.8-8.0, at 60 degrees C for 5-6 h. The intermediate beta-ketocarboxylate is smoothly decarboxylated in the reaction medium, giving the beta-ketol in high yield (75-90%). Acidification of the reaction mixture at pH 1 and heating at 70 degrees C under vigorous stirring for 6 h, leads directly to the corresponding alpha,beta-unsaturated ketone in good yield (65-75%).     

Dibenzo[b,h][1,4,7]thiadiazonines: examples of a novel ring system

Acetanilides 1a-e react with 1,1'-sulfinylbis(benzotriazole)/trimethylchlorosilane at 45-65 degrees C to form 1,2-di(benzotriazol-1-yl)-2-arylimino-1-ethanethiones 3a-e, while heating the same reagents at 110 degrees C results in dibenzo[b,h][1,4,7]thiadiazonines 5a,c,d, and 6. X-ray crystal structures are reported for three representative examples.     

Lithiation of 1-chloromethylbenzotriazole: generation and elaboration of benzotriazolyloxiranes

1-Benzotriazolylchloromethyllithium generated from 1-chloromethylbenzotriazole (1) and LDA reacts with enolizable and nonenolizable ketones to give benzotriazolyloxiranes 2a-g in good yields. The oxiranyllithiums 4a-d generated from 2a-d and n-BuLi at -78 degrees C were trapped by a variety of electrophiles to give oxiranyl derivatives 5a-j in good to excellent yields. Lewis-acid-promoted nucleophilic ring opening of benzotriazolyloxiranes 2a,f,g with allyltrimethylsilane gave the corresponding 1,7-octadien-4-ols 6a-c in 68-75% yield. Hydrolysis of alpha-acylbenzotriazolyloxiranes 5g,h provided 3-hydroxy-1,2-diones 7a and 7b in 73 and 86% yield, respectively.     

The synthesis and characterization of compounds of the type Hg[1-C(6)H(4)-2-C(H)=NC(6)H(5-n)R(n)](2)

The organomercurial compounds Hg[1-C(6)H(4)-2-C(H)=NC(6)H(5-n)R(n)](2) (R = 4-NMe(2), 6a; 4-Me, 6b; 4-I, 6c; 4-NO(2), 6d; 2-(i)Pr, 6e; 2-Me, 6f; 2,6-(i)Pr(2), 6g; 2,6-Me(2), 6h) have been prepared in good overall yield from 2-bromobenzaldehyde. All of the compounds have been characterized by elemental analysis, (1)H NMR, (13)C[(1)H] NMR, and infrared spectroscopy. In addition, compounds 6a [C(30)H(30)HgN(4), triclinic, P, a = 6.20000(10) A, b = 9.2315(2) A, c = 10.9069(3) A, alpha = 85.8510(10) degrees, beta = 89.3570(10) degrees, gamma = 87.206(2) degrees, Z = 1], 6b [C(28)H(24)HgN(2), monoclinic, P2(1)/c, a = 12.8260(5) A, b = 14.0675(4) A, c = 6.1032(2) A, beta = 90.0990(10) degrees, Z = 2], 6g [C(38)H(44)HgN(2), triclinic, P, a = 8.2626(2) A, b = 9.8317(2) A, c = 11.8873(3) A, alpha = 103.6650(10) degrees, beta = 109.3350(10) degrees, gamma = 104.627(2) degrees, Z = 1], and 6h [C(30)H(28)HgN(2), monoclinic, P2(1)/c, a = 12.5307(2) A, b = 10.9852(2) A, c = 18.2112(2) A, beta = 104.0190(10) degrees, gamma = 87.206(2) degrees, Z = 4] have been characterized by low-temperature single-crystal X-ray diffraction studies, and two different molecular geometries about the central mercury atom have been observed; intramolecular contacts suggest a van der Waals radius for Hg of 2.1-2.2 A.     

X-ray Crystal Structure, ab Initio Calculations, and Reactivity of 1,3,2lambda(5)-Diazaphosphetes: A New Type of 4-pi-Electron 4-Membered Heterocycle

The structure of P,P-bis(diisopropylamino)-4-phenyl-1,3,2lambda(5)-diazaphosphete, 1a, has been determined by a single-crystal X-ray diffraction study (C(19)H(33)N(4)P, monoclinic system, space group P2(1), a = 9.482(1) ?, b = 11.374(3) ?, c = 9.668(2) ?, beta = 97.16(1) degrees, Z = 2). According to quantum chemical calculations at an RHF level of optimization utilizing the 6-31g(d,p) basis set, 1a has a zwitterionic structure with the negative charge delocalized on the NCN allylic fragment and the positive charge localized at the phosphorus. Heterocycle 1a reacts with water and benzaldehyde affording N-phosphoranylbenzamidine 3 (95% yield) and the expected aza-Wittig adduct 4 (85% yield), respectively. Addition of 1 equiv of methyl trifluoromethanesulfonate and of 2 equiv of BH(3).THF to 1a affords cyclic phosphonium salt 5 (94% yield) and the bis(borane) adduct 6a (90% yield), respectively. Dimethyl acetylenedicarboxylate slowly reacts with 1a giving rise to 1,3,4lambda(5)-diazaphosphinine, 9, in 70% yield. The X-ray crystal structures of products 2,3, and 6a are reported (2: C(26)H(38)N(5)P, monoclinic system, space group C2/c, a = 16.337(8) ?, b = 19.810(2) ?, c = 8.800(2) ?, beta = 117.68(2) degrees, Z = 4. 3: C(19)H(35)N(4)OP, orthorhombic system, space group P2(1)2(1)2(1), a = 9.090(1) ?, b = 12.955(2) ?, c = 17.860(3) ?, Z = 4. 6a: C(19)H(39)B(2)N(4)P, orthorhombic system, space group P2(1)2(1)2(1), a = 10.340(1) ?, b = 13.247(1) ?, c = 16.996(1) ?, Z = 4).     

B(C6F5)3- vs Al(C6F5)3-derived metallocenium ion pairs. Structural, thermochemical, and structural dynamic divergences

The thermodynamic and structural characteristics of Al(C6F(5)3-derived vs B(C6F5)3-derived group 4 metallocenium ion pairs are quantified. Reaction of 1.0 equiv of B(C6F5)3 or 1.0 or 2.0 equiv of Al(C6F5)3 with rac-C2H4(eta5-Ind)2Zr(CH3)2 (rac-(EBI)Zr(CH3)2) yields rac-(EBI)Zr(CH3)(+)H3CB(C6)F5)(3)(-) (1a), rac-(EBI)Zr(CH3)+H3CAl(C6F5)(3)(-) (1b), and rac-(EBI)Zr2+[H3CAl(C6F5)3](-)(2) (1c), respectively. X-ray crystallographic analysis of 1b indicates the H3CAl(C6F5)(3)(-) anion coordinates to the metal center via a bridging methyl in a manner similar to B(C6F5)3-derived metallocenium ion pairs. However, the Zr-(CH3)(bridging) and Al-(CH3)(bridging) bond lengths of 1b (2.505(4) A and 2.026(4) A, respectively) indicate the methyl group is less completely abstracted in 1b than in typical B(C6F5)3-derived ion pairs. Ion pair formation enthalpies (DeltaH(ipf)) determined by isoperibol solution calorimetry in toluene from the neutral precursors are -21.9(6) kcal mol(-1) (1a), -14.0(15) kcal mol(-1) (1b), and -2.1(1) kcal mol(-1) (1b-->1c), indicating Al(C6F5)3 to have significantly less methide affinity than B(C6F5)3. Analogous experiments with Me2Si(eta5-Me4C5)(t-BuN)Ti(CH3)2 indicate a similar trend. Furthermore, kinetic parameters for ion pair epimerization by cocatalyst exchange (ce) and anion exchange (ae), determined by line-broadening in VT NMR spectra over the range 25-75 degrees C, are DeltaH++(ce) = 22(1) kcal mol(-1), DeltaS++(ce) = 8.2(4) eu, DeltaH++(ae) = 14(2) kcal mol(-1), and DeltaS++(ae) = -15(2) eu for 1a. Line broadening for 1b is not detectable until just below the temperature where decomposition becomes significant ( approximately 75-80 degrees C), but estimation of the activation parameters at 72 degrees C gives DeltaH++(ce) approximately 22 kcal mol(-1)and DeltaH++(ae) approximately 16 kcal mol(-1), consistent with the bridging methide being more strongly bound to the zirconocenium center than in 1a.     

Ambient temperature activation of haloporphyrinic-enediynes: electronic contributions to bergman cycloaromatization

We have synthesized the nickel(II) 2,3-bis(haloethynyl)-5,10,15,20-tetraphenylporphyrins with -Br (2a) or -I (2b) at the alkyne termini position from the corresponding 2,3-diethynyl analogue (1). The cross coupling of nickel(II) 2,3-dibromo-5,10,15,20-tetraphenylporphyrin with trimethyl(trimethylstannanylethynyl)silane in the presence of a Pd0 catalyst and subsequent deprotection with base under aqueous conditions yields the nickel(II) 2,3-diethynyl-5,10,15,20-tetraphenylporphyrin (1). Subsequent reaction of 1 with N-bromo- or N-iodosuccinimide in dry acetone in the presence of AgNO3 yields 2,3-bis(haloethynyl)-5,10,15,20-tetraphenylporphyrins in 70% (2a) and 68% (2b) yields. The X-ray crystal structures of 2a,b show that the porphyrin backbone deviates significantly from planarity due to a Ni(II)-induced mixture of the classic ruffle and saddle distortions. Thermolysis of 2a at 190 degrees C for 6 h in chlorobenzene and 30-fold 1,4-cyclohexadiene (CHD) generates the Bergman cyclized nickel(II) dibromopicenoporphyrin product (3) in 65% yield, which derives from diradical addition across the adjacent meso-phenyl substituents. Similarly, nickel(II) 2,3-bis(iodoethynyl)-5,10,15,20-tetraphenylporphyrin, 2b, cyclizes at 190 degrees C in chlorobenzene/CHD via high-temperature substitution of iodine by hydrogen (from CHD) or chlorine (from solvent) to afford a mixture of 4 (15%) and 5 (45%). Remarkably, ambient temperature incubation of 2a in MeOH/CHCl3 (1:3, 22 h) or chlorobenzene/CHD (3:1, 24 h) leads to generation of 3 in 15% and 22% isolated yields, respectively. Addition of 1.2 equiv of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in CHCl3/MeOH dramatically accelerates the rate of reaction, producing 3 in 30% yield within 0.5 h. The origin of the ambient temperature activation of 2a derives from the ability of electron-withdrawing functionalities at the alkyne termini to decrease the activation barrier to the Bergman product.     

Intermolecular 2hJNN coupling in multiply hydrogen-bonded ureidopyrimidinone dimers in solution

15N-Labeled ureido-4[1H]-pyrimidinones 4a and 5a were synthesized in order to investigate hydrogen bonding in the strongly hydrogen-bonded dimers in solution with intermolecular (2h)J(NN) coupling. Both direct-detection (15)N NMR and one-dimensional (15)N INADEQUATE (for smaller scalar coupling constants) were employed to determine the coupling constants. For dimers of 4 in CDCl(3), a temperature-dependent (2h)J(NN) was observed ranging from 2 Hz at +10 degrees C to 5.1 Hz at -20 degrees C. In dimers of more slowly exchanging bifunctional derivative 5, the coupling constants could be determined at room temperature from an inverse-gated (1)H-decoupled (15)N NMR experiment. Coupling constants in different isomers of the dimer of 5a (4.96, 5.13, 4.37, and 5.27 Hz) were used to test the relationship between (2h)J(NN) values and N-N distances as proposed by Del Bene et al. The N-N distances calculated with the aid of this relationship show excellent agreement with the distances observed in the X-ray crystal structures of 5b, particularly when the nonlinearity of the hydrogen bonds is taken into account.     

An investigation of Staudinger reactions involving cis-1,3,5-triazidocyclohexane and tri(alkylamino)phosphines

The reaction of 1,3,5-cis-triazidocyclohexane with the electron-rich tris(dialkylamino)phosphines P(NMe(2))(3) (1) and N(CH(2)CH(2)NMe)(3)P (2b) in acetonitrile for 3 h furnished the corresponding tris-phosphazides 1,3,5-cis-(R(3)PN(3))(3)C(6)H(9), 3a (R(3)P = 1) and 3b (R(3)P = 2b), in 90% and 92% yields, respectively. The same reaction with the relatively electron-poor tris(dialkylamino)phosphine MeC(CH(2)NMe)(3)P (4) for 2 days gave the tris-iminophosphorane, 1,3,5-cis-(R(3)PN)(3)C(6)H(9), 5a (R(3)P = 4), in 60% yield. Compound 3b is a thermally stable solid that did not lose dinitrogen when refluxed in toluene for 24 h or when heated as a neat sample at 100 degrees C /0.5 Torr for 10 h. By contrast, tris-phosphazide 3a decomposed to the tris-iminophosphorane 1,3,5-cis-(R(3)PN)(3)C(6)H(9), 5b (R(3)P = 1), in 3 h in quantitative yield upon heating to 100 degrees C in toluene. Factors influencing the formation of the phosphazides or the iminophosphoranes in these reactions are discussed. The reaction of 3b with 4 equiv of benzoic acid gave [N(CH(2)CH(2)NMe)(3)P=NH(2)]PhCO(2) ([6bH]PhCO(2)) in quantitative yield along with benzene (56% yield) and dinitrogen. The same reaction with 3a gave [(Me(2)N)(3)P=NH(2)]PhCO(2) ([7aH]PhCO(2)) (quantitative yield), benzene (15% yield), and dinitrogen(.) Treatment of [6bH]PhCO(2) with KO(t)Bu afforded N(CH(2)CH(2)NMe)(3)P=NH (6b) in 40% overall yield. Compound 6b upon treatment with PhCH(2)CH(2)Br produced [6bH]Br in 90% yield along with styrene. The new compounds were characterized by analytical and spectroscopic methods, and selected compounds (3b, 5a, and [6bH]Br) were structured by X-ray crystallography. A special feature of 3b is its capability to function as a starting material for 6b, which was not accessible by other synthetic routes.     

Furopyridines. XIII. Reaction of 2-methylfuro[2,3-b]-, -[3,2-b]-, -[2,3-c]- and -[3,2-c]pyridines with lithium diisopropylamide

Lithiation of 2-methylfuro[2,3-b]- 1a , -[2,3-c]- 1c and -[3,2-c]pyridine 1d with lithium diisopropylamide at ?75° and subsequent treatment with deuterium chloride in deuterium oxide afforded 2-monodeuteriomethyl compounds 2a, 2c and 2d , while 2-methylfuro[3,2-b]pyridine 1b gave a mixture of 1b, 2b , 2-methyl-3-deuteriofuro[3,2-b]pyridine 2′b and 2-(1-proynyl)pyridin-3-ol 5 . The same reaction of 1a at ?40° gave 3-(1,2-propadienyl)pyridin-2-ol 3 and 3-(2-propynyl)pyridin-2-ol 4 . Reaction of the lithio intermediates from 1a, 1c and 1d with benzaldehyde, propionaldehyde and acetone afforded the corresponding alcohol derivatives 6a, 6c, 6d, 7a, 7c, 7d, 8a, 8c and 8d in excellent yield; while the reaction of lithio intermediate from 1b gave the expected alcohols 6b and 8b in lower yields accompanied by formation of 3-alkylated compounds 9, 11, 12 and compound 5 . While reaction of the intermediates from 1a, 1b and 1d with N,N-dimethylacetamide yielded the 2-acetonyl compounds 13a, 13b and 13d in good yield, the same reaction of 1c did not give any acetylated product but recovery of the starting compound almost quantitatively.     

Facile preparation of Hexahydropyrrolo

Chlorolactames 2a-f reacted with sodium azide to give the cyclopropylketimines 3a-f (75-89%), and acid hydrolysis of 3c,d yielded the cyclopropylketones 6c,d (61-67%). Compounds 3a-f and 6c, d were transformed by heating (170-240 degrees C, sublimation) to the air-sensitive dihydropyrroles 4a-f (51-71%) and dihydrofurans 7c, d (85-91%). Oxidation of the dihydro derivatives 4a-f and 7c,d with DDQ led to novel types of pyrrolo[3,2-e][1,4]diazepinedione derivatives 5a-f (75-84%) and furo[1H][3,2-e][1,4]diazepinediones 8c, d (91-93%).     

Asymmetric synthesis of metallocenes through enantioselective addition of organolithium reagents to 6-(dimethylamino)fulvene

Enantioselective addition of aryllithiums 2a-d (Ar = Ph (a), 2-MeC(6)H(4) (b), 2-MeOC(6)H(4) (c), 1-naphthyl (d)) to 6-(dimethylamino)fulvene (1) in the presence of (-)-sparteine in toluene at -78 degrees C generated chiral cyclopentadienyllithiums (4) substituted with an N,N-dimethylamino(aryl)methyl group, where the enantioselectivities are 51, 91, 90, and 83% for 4a, 4b, 4c, and 4d, respectively. Treatment of the chiral cyclopentadienides 4 with FeCl(2) or Fe(acac)(2) gave ferrocenes, which contain an N,N-dimethylamino(aryl)methyl side chain on both of the cyclopentadienyl rings. The enantiomeric purity of the chiral ferrocenes 7 thus obtained is 99% ee or higher for those containing a 2-MeC(6)H(4) (7b) or a 2-MeOC(6)H(4) (7c) group.     

Alkene metatheses in transition metal coordination spheres: dimacrocyclizations that join trans positions of square-planar platinum complexes to give topologically novel diphosphine ligands

The alkene-containing phosphines PPh((CH2)(n)CH=CH2)2)2 are prepared from PPhH(2), n-BuLi, and the corresponding bromoalkenes (1:2:2), and combined with the platinum tetrahydrothiophene complex [Pt(mu-Cl)(C(6)F(5))(S(CH2CH2(-))2)]2 to give the square-planar adducts trans-(Cl)(C(6)F(5))Pt(PPh((CH2)(n)CH=CH2)2)2 (11, 93-73%; n=a, 2; b, 3; c, 4; d, 5; e, 6; f, 8). Ring-closing metatheses with Grubbs' catalyst (2) are studied. With, two isomers of trans-(Cl)(C6F5)[formula: see text](14)Ph)(15e) are isolated after hydrogenation. Both form via dimacrocyclization between the trans-phosphine ligands, but differ in the dispositions of the PPh rings (syn, 31%; anti, 7%). The alternative intraligand metathesis product trans-(Cl)(C6F5)[formula: see text](14)Ph)2 (16e) is independently prepared by (i) protecting 4e as a borane adduct, H(3)B.PPh((CH(2))(6)CH=CH2)2, (ii) cyclization with 2 and hydrogenation to give H(3)B[formula: see text] (14), (iii) deprotection and reaction with 12. The sample derived from 11e contains < or = 2% 16e; mass spectra suggest that the other products are dimers or oligomers. The structures of syn-15e, anti-15e and 16e are verified crystallographically, and the macrocycle conformations analyzed. As expected from the (CH(2))(n) segment length, 11a undergoes intraligand metathesis to give (Z,Z)-trans-(Cl)(C6F5)Pt[formula: see text]CH2)2)2 (86%), as confirmed by a crystal structure of the hydrogenation product. Although 11b does not yield tractable products, 11c gives syn-(E,E)-trans-(Cl)(C6F5[formula:see text](21%). This structure, and that of the hydrogenation product (syn-15c; 95%), are verified crystallographically. Analogous sequences with 11d,f give syn-15d (5 and 14% overall).     

3-Aza-cope rearrangement of quaternary N-allyl enammonium salts. Stereospecific 1,3 allyl migration from nitrogen to carbon on a tricyclic template

N-Allyl enamines can undergo a [3,3] sigmatropic rearrangement known as a 3-aza-Cope (or amino-Claisen) reaction. We explored a 3-aza-Cope reaction involving 1,3 allylic migration from nitrogen to carbon in N-allyl enammonium quaternary salts, exemplified by benzo[a]quinolizine 8 and pyrrolo[2,1-a]isoquinoline 13, with an interest in stereochemistry and mechanism. Salts 8 and 13 were accessed, respectively, through stereospecific allylation of hydroxy amines 4 and 11a/11b to give 7 and 12a/12b, which were dehydrated with trifluoroacetic acid. Allylic migration in these tricyclic tetrahydroisoquinolines occurred with high stereospecificity, with the major products 9 (from 8) and 15a (from 13) apparently deriving from a concerted suprafacial [3,3] rearrangement. The rearrangement of 8 to 9 was facile at 23 degrees C (t(1/2) = ca. 5 h) and was >98% stereospecific, whereas the rearrangement of 13 to 15a/15b required heating between 50 and 100 degrees C, with ca. 90-95% stereospecificity (t(1/2) = ca. 0.3 h at 100 degrees C). A deuterium-labeling experiment with 21 ((2)H-13) confirmed that allylic inversion accompanies the 1,3 migration en route to major isomer 22a ((2)H-15a), supporting the predominance of a concerted [3, 3] sigmatropic mechanism. However, the 5-10% loss of stereospecificity in the rearrangements of the pyrroloisoquinolines 13 and 21, reflected by formation of minor isomers 15b and 22b, respectively, indicates a minor nonconcerted reaction pathway.     

Ruthenium-catalyzed C-C bond forming transfer hydrogenation: carbonyl allylation from the alcohol or aldehyde oxidation level employing acyclic 1,3-dienes as surrogates to preformed allyl metal reagents

Under the conditions of ruthenium-catalyzed transfer hydrogenation, commercially available acyclic 1,3-dienes, butadiene, isoprene, and 2,3-dimethylbutadiene, couple to benzylic alcohols 1a-6a to furnish products of carbonyl crotylation 1b-6b, carbonyl isoprenylation 1c-6c, and carbonyl reverse 2-methyl prenylation 1d-6d. Under related transfer hydrogenation conditions employing isopropanol as terminal reductant, isoprene couples to aldehydes 7a-9a to furnish identical products of carbonyl isoprenylation 1c-3c. Thus, carbonyl allylation is achieved from the alcohol or the aldehyde oxidation level in the absence of preformed allyl metal reagents. Coupling to aliphatic alcohols (isoprene to 1-nonanol, 65% isolated yield) and allylic alcohols (isoprene to geraniol, 75% isolated yield) also is demonstrated. Isotopic labeling studies corroborate a mechanism involving hydrogen donation from the reactant alcohol or sacrificial alcohol (i-PrOH).     

Photochemical Reactions. Part 64 [1]. The photochemistry of 3-alkyl-cyclopent-2-en-ones

On ultraviolet irradiation in toluene, cyclopent-2-en-one ( 1a ) and 3-methylcyclopent-2-en-one ( 1b ) undergo dimerisation (→ 3a, b, 4b ), whereas 3-t-butyl-cyclopent-2-en-one ( 1e ) and the bicyclo [3.2.1]octenone 2a only react with the solvent (→ 5e–7e, 8–10 ). The 3-ethyl-( 1c ) and 3-isopropyl-cyclopent-2-en-ones ( 1d ) afford by dimerisation products 3c, d, 4c and by reaction with the solvent 5c, d, 6c, d, 7d . The β-methoxy-enones 1f and 2b are unreactive under comparable irradiation conditions. The head-to-head cyclobutane dimer 3b (HH) by separate irradiation at < 3400 Å in toluene, is reconverted to 1b . By similar irradiation each of the head-to-tail dimers 3b (anti- and syn-HT) and also the unsaturated dimer 4b give a new isomer of unknown structure besides small amounts of monomer 1b and relatively large amounts of insoluble material. The photoreactions of 1b-e can be quenched by naphthalene. Stern-Volmer plots for the quenching of the dimers of 1b, 1c , and 1d , and of 3-t-butylcyclopentanone ( 5e ) and the dihydro dimer 7e are linear and within each experiment, the slopes satisfactorily coincide, whereas the slope for the α-benzyl ketone 6c is distinctly greater than that for the dimers 3c . A similar differentiation, although less pronounced, is found between the benzyl ketones 6d and 6e and the respective accompanying products.     

Highly sulfurated heterocycles via dithiiranes and trithietanes as key intermediates

2,2,4,4-Tetramethyl-3-thioxocyclobutanone (8b) easily reacts with gaseous chlorine to yield the stable alpha-chloro sulfenyl chloride 10. The same product was obtained when 8b was treated either with phosphorus pentachloride (PCl(5)) or sulfuryl chloride (SO(2)Cl(2)) in CCl(4) solution. Sulfur dichloride (SCl(2)) reacts with 8b to give the alpha-chloro thiosulfenyl chloride 12 along with an almost equimolar amount of the trisulfide 13b. The less reactive disulfur dichloride (S(2)Cl(2)) was shown to react slowly with 8b and the symmetrical tetrasulfide 15 was found as the exclusive product. The pure thiosulfenyl chloride 12 added to adamantanethione (8c) yielded the unsymmetrical trisulfide 13c. When 12 was treated with thioacetic acid, the acetylated trisulfide 17 was formed in high yield. "Unzipping" reactions with the acetylated disulfide 16 and trisulfide 17 with morpholine in THF at -40 degrees C led to the formation of mixtures of two sulfur-rich heterocycles identified as the pentathiepane 6b and the hexathiepane 7b. A mixture of analogous products was obtained when alpha-chloro sulfenyl chloride 10 was treated with sodium sulfide in anhydrous THF at -40 degrees C. The formation of 6b and 7b is believed to occur via the intermediate dithiirane 1b and/or the isomeric thiosulfine 2b. In the case of 17 the reaction starts probably with the formation of a nonisolable tetrathiane 18b as presented in Scheme 5.