Platinum(II) Complexes of P‐Chiral 1, 8‐Bis(diorganophosphino)naphthalenes; Crystal Structures of dmfppn,rac‐[PtCl2(dmfppn)], and rac‐[PtCl2(dtbppn)] (dmfppn = 1, 8‐di(methyl‐pentafluorophenylphosphino)naphthalene and dtbppn = 1, 8‐di(tert‐butylphenylphosphino)naphthalene)

The reaction of 1, 8‐dilithionaphthalene 2 , with 2 equivalents of rac‐Me(C₆F₅)PCl, gave a 6 : 1 mixture of rac‐ and meso‐1, 8‐di(methyl‐pentafluorophenylphosphino)naphthalene (dmfppn, rac‐ 3h and meso‐ 3h ), but no reaction was observed when the sterically crowded rac‐tBu(C₆F₅)PCl was used. In ³¹P NMR experiments, rac‐ 3h and mmeso‐ 3h exhibited characteristic signals (virtual quintets), which indicate that there is significant coupling through space (³J_PF + ⁷ J_PF ≈ 15 Hz). Compound rac‐ 3h was isolated by fractional crystallisation and treated with aqueous H₂O₂ to yield the corresponding bis‐phosphine dioxide, rac‐ 7h . In contrast to rac‐ 3h , there was no sign of through‐space coupling in rac‐ 7h , which again illustrates that the latter operates via the lone pairs at phosphorus. Platinum(II) complexes were prepared from the new, P‐chiral chelate rac‐ 3h , and the related ligand 1, 8‐di(tert‐butylphenylphosphino) naphthalene (rac‐dtbppn, rac‐ 3e ). All isolated new compounds were characterised by multinuclear NMR and IR spectroscopy, mass spectrometry, and elemental analysis. Single‐crystal X‐ray structure determinations were performed for rac‐dmfppn (rac‐ 3h ), rac‐[PtCl₂(dtbppn)] (rac‐ 17e ), and rac‐[PtCl₂(dmfppn)] (rac‐ 17h ). rac‐ 3h displays crystallographic twofold symmetry. In rac‐ 17h , the electron‐withdrawing effect of the C₆F₅ groups causes a shortening of the P_t—P bond to ca. 220 pm (cf. 223 pm in rac‐ 17e ).     

Room‐temperature Suzuki–Miyaura cross‐coupling reaction with α‐diimine Pd(II) catalysts

An α‐diimine Pd(II) complex containing chiral sec‐phenethyl groups, {bis[N,N′‐(4‐methyl‐2‐sec‐phenethylphenyl)imino]‐2,3‐butadiene}dichloropalladium (rac‐ C1 ), was synthesized and characterized. rac‐ C1 was applied as an efficient catalyst for the Suzuki–Miyaura cross‐coupling reaction between various aniline halides and arylboronic acid in PEG‐400–H₂O at room temperature. Among a series of aniline halides, rac‐ C1 did not catalyze the cross‐coupling of aniline chlorides and fluorides but efficiently catalyzed the cross‐coupling of aniline bromides and iodides with phenylboronic acid. The catalytic activity reduced slightly with increasing steric hindrance of the aniline bromides. The complexes {bis[N,N′‐(4‐fluoro‐2,6‐diphenylphenyl)imino]‐2,3‐butadiene}dichloropalladium and {bis[N,N′‐(4‐fluoro‐2,6‐diphenylphenyl)imino]acenaphthene}dichloropalladium were also found to be efficient catalysts for the reaction. Copyright © 2015 John Wiley & Sons, Ltd.     

Disila‐Galaxolide and Derivatives: Synthesis and Olfactory Characterization of Silicon‐Containing Derivatives of the Musk Odorant Galaxolide

A series of silicon‐containing derivatives of the polycyclic musk odorant galaxolide ( 4 a ) was synthesized, that is, disila‐galaxolide ((4RS,7SR)‐ 4 b /(4RS,7RS)‐ 4 b ), its methylene derivative rac‐ 9 , and its nor analogue rac‐ 10 . The tricyclic title compounds with their 7,8‐dihydro‐6,8‐disila‐6 H‐cyclopenta[g]isochromane skeleton were prepared in multistep syntheses by using a cobalt‐catalyzed [2+2+2] cycloaddition of the mono‐ yne H₂C?CHCH₂OCH₂C?CB(pin) (B(pin)=4,4,5,5‐tetramethyl‐1,3,2‐di‐ oxaborolan‐2‐yl) with the diynes H₂C?C[Si(CH₃)₂C?CH]₂ or H₂C‐ [Si(CH₃)₂C?CH]₂ as the key step. Employing [Cr(CO)₃(MeCN)₃] as an auxiliary, the disila‐galaxolide diastereomers (4RS,7SR)‐ 4 b and (4RS,7RS)‐ 4 b could be chromatographically separated through their tricarbonylchromium(0) complexes, followed by oxidative decomplexation. The identity of the title compounds and their precursors was established by elemental analyses and multinuclear NMR spectroscopic studies and in some cases additionally by crystal structure analyses. Compounds (4RS,7SR)‐ 4 b , (4RS,7RS)‐ 4 b , rac‐ 9 , and rac‐ 10 were characterized for their olfactory properties, including GC‐olfactory studies of the racemic compounds on a chiral stationary phase. As for the parent galaxolide stereoisomers 4 a , only one enantiomer of the silicon compounds (4RS,7SR)‐ 4 b , (4RS,7RS)‐ 4 b , rac‐ 9 , and rac‐ 10 , smelt upon enantioselective GC‐olfactometry, which according to the elution sequence is assumed to be also (4S)‐configured as in the case of the galaxolide stereoisomers. The disila‐analogues (4S,7R)‐ 4 b and (4S,7S)‐ 4 b were, however, about one order of magnitude less intense in terms of their odor threshold than their parent carbon compounds (4S,7R)‐ 4 a and (4S,7S)‐ 4 a . The introduction of a 7‐methylene group in disila‐galaxolide ( 4 b →rac‐ 9 ) improved the odor threshold by a factor of two. With the novel silicon‐containing galaxolide derivatives, the presumed hydrophobic bulk binding pocket of the corresponding musk receptor(s) could be characterized in more detail, which could be useful for the design of novel musk odorants with an improved environmental profile.     

Oxidative Fragmentations of the 5α‐ and 5β‐Hydroxy‐B‐norcholestan‐ 3β‐yl Acetates

Oxidations of 5α‐hydroxy‐B‐norcholestan‐3β‐yl acetate ( 8 ) with Pb(OAc)₄ under thermal or photolytic conditions or in the presence of iodine afforded only complex mixtures of compounds. However, the HgO/I₂ version of the hypoiodite reaction gave as the primary products the stereoisomeric (Z)‐ and (E)‐1(10)‐unsaturated 5,10‐seco B‐nor‐derivatives 10 and 11 , and the stereoisomeric (5R,10R)‐ and (5S,10S)‐acetals 14 and 15 (Scheme 4). Further reaction of these compounds under conditions of their formation afforded, in addition, the A‐nor 1,5‐cyclization products 13 and 16 (from 10 ) and 12 (from 11 ) (see also Scheme 6) and the 6‐iodo‐5,6‐secolactones 17 and 19 (from 14 and 15 , resp.) and 4‐iodo‐4,5‐secolactone 18 (from 15 ) (see also Scheme 7). Oxidations of 5β‐hydroxy‐B‐norcholestan‐3β‐yl acetate ( 9 ) with both hypoiodite‐forming reagents (Pb(OAc)₄/I₂ and HgO/I₂) proceeded similarly to the HgO/I₂ reaction of the corresponding 5α‐hydroxy analogue 8 . Photolytic Pb(OAc)₄ oxidation of 9 afforded, in addition to the (Z)‐ and (E)‐5,10‐seco 1(10)‐unsaturated ketones 10 and 11 , their isomeric 5,10‐seco 10(19)‐unsaturated ketone 22 , the acetal 5‐acetate 21 , and 5β,19‐epoxy derivative 23 (Scheme 9). Exceptionally, in the thermal Pb(OAc)₄ oxidation of 9 , the 5,10‐seco ketones 10, 11 , and 22 were not formed, the only reaction being the stereoselective formation of the 5,10‐ethers with the β‐oriented epoxy bridge, i.e. the (10R)‐enol ether 20 and (5S,10R)‐acetal 5‐acetate 21 (Scheme 8). Possible mechanistic interpretations of the above transformations are discussed.     

Analogues of α‐Campholenal (= (1R)‐2,2,3‐Trimethylcyclopent‐3‐ene‐1‐acetaldehyde) as Building Blocks for (+)‐β‐Necrodol (= (1S,3S)‐2,2,3‐Trimethyl‐4‐methylenecyclopentanemethanol) and Sandalwood‐like Alcohols

To complete our panorama in structure–activity relationships (SARs) of sandalwood‐like alcohols derived from analogues of α‐campholenal (= (1R)‐2,2,3‐trimethylcyclopent‐3‐ene‐1‐acetaldehyde), we isomerized the epoxy‐isopropyl‐apopinene (?)‐ 2d to the corresponding unreported α‐campholenal analogue (+)‐ 4d (Scheme 1). Derived from the known 3‐demethyl‐α‐campholenal (+)‐ 4a , we prepared the saturated analogue (+)‐ 5a by hydrogenation, while the heterocyclic aldehyde (+)‐ 5b was obtained via a Bayer‐Villiger reaction from the known methyl ketone (+)‐ 6 . Oxidative hydroboration of the known α‐campholenal acetal (?)‐ 8b allowed, after subsequent oxidation of alcohol (+)‐ 9b to ketone (+)‐ 10 , and appropriate alkyl Grignard reaction, access to the 3,4‐disubstituted analogues (+)‐ 4f,g following dehydration and deprotection. (Scheme 2). Epoxidation of either (+)‐ 4b or its methyl ketone (+)‐ 4h , afforded stereoselectively the trans‐epoxy derivatives 11a,b , while the minor cis‐stereoisomer (+)‐ 12a was isolated by chromatography (trans/cis of the epoxy moiety relative to the C₂ or C₃ side chain). Alternatively, the corresponding trans‐epoxy alcohol or acetate 13a,b was obtained either by reduction/esterification from trans‐epoxy aldehyde (+)‐ 11a or by stereoselective epoxidation of the α‐campholenol (+)‐ 15a or of its acetate (?)‐ 15b , respectively. Their cis‐analogues were prepared starting from (+)‐ 12a . Either (+)‐ 4h or (?)‐ 11b , was submitted to a Bayer‐Villiger oxidation to afford acetate (?)‐ 16a . Since isomerizations of (?)‐ 16 lead preferentially to β‐campholene isomers, we followed a known procedure for the isomerization of (?)‐epoxyverbenone (?)‐ 2e to the norcampholenal analogue (+)‐ 19a . Reduction and subsequent protection afforded the silyl ether (?)‐ 19c , which was stereoselectively hydroborated under oxidative condition to afford the secondary alcohol (+)‐ 20c . Further oxidation and epimerization furnished the trans‐ketone (?)‐ 17a , a known intermediate of either (+)‐β‐necrodol (= (+)‐(1S,3S)‐2,2,3‐trimethyl‐4‐methylenecyclopentanemethanol; 17c ) or (+)‐(Z)‐lancifolol (= (1S,3R,4Z)‐2,2,3‐trimethyl‐4‐(4‐methylpent‐3‐enylidene)cyclopentanemethanol). Finally, hydrogenation of (+)‐ 4b gave the saturated cis‐aldehyde (+)‐ 21 , readily reduced to its corresponding alcohol (+)‐ 22a . Similarly, hydrogenation of β‐campholenol (= 2,3,3‐trimethylcyclopent‐1‐ene‐1‐ethanol) gave access via the cis‐alcohol rac‐ 23a , to the cis‐aldehyde rac‐ 24 .     

First Synthesis of Azachlorins and Azacorrins with a N‐Atom in β‐Pyrrolic Positions

Azachlorins 7 and 11 , and azahexadehydrocorrin rac‐ 10 are novel structural types of tetrapyrrolic macrocycles. Synthesis of the target structures bearing N‐atoms in the β‐periphery of the macrotetracycles could be achieved by attaching an imidazole moiety 4 to the tricyclic Ni complex rac‐ 5 , followed by cyclization. Depending on the central metal ion of the bilin intermediates rac‐ 6a and rac‐ 6b , chlorin‐ or corrin‐type structures were formed by cyclization.     

Gold(III) Chloride Catalyzed Synthesis of Chiral Substituted 3‐Formyl Furans from Carbohydrates: Application in the Synthesis of 1,5‐Dicarbonyl Derivatives and Furo[3,2‐c]pyridine

This report describes a gold(III)‐catalyzed efficient general route to densely substituted chiral 3‐formyl furans under extremely mild conditions from suitably protected 5‐(1‐alkynyl)‐2,3‐dihydropyran‐4‐one using H₂O as a nucleophile. The reaction proceeds through the initial formation of an activated alkyne–gold(III) complex intermediate, followed by either a domino nucleophilic attack/anti‐endo‐dig cyclization, or the formation of a cyclic oxonium ion with subsequent attack by H₂O. To confirm the proposed mechanistic pathway, we employed MeOH as a nucleophile instead of H₂O to result in a substituted furo[3,2‐c]pyran derivative, as anticipated. The similar furo[3,2‐c]pyran skeleton with a hybrid carbohydrate–furan derivative has also been achieved through pyridinium dichromate (PDC) oxidation of a substituted chiral 3‐formyl furan. The corresponding protected 5‐(1‐alkynyl)‐2,3‐dihydropyran‐4‐one can be synthesized from the monosaccharides (both hexoses and pentose) following oxidation, iodination, and Sonogashira coupling sequences. Furthermore, to demonstrate the potentiality of chiral 3‐formyl furan derivatives, a TiBr₄‐catalyzed reaction of these derivatives has been shown to offer efficient access to 1,5‐dicarbonyl compounds, which on treatment with NH₄OAc in slightly acidic conditions afforded substituted furo[3,2‐c]pyridine.     

Synthesis of α‐(Fluorophenyl)pyridine by Palladium‐Catalyzed Cross‐Coupling Reaction

A series of α‐(fluoro‐substituted phenyl)pyridines have been synthesized by means of a palladium‐catalyzed cross‐coupling reaction between fluoro‐substituted phenylboronic acid and 2‐bromopyridine or its derivatives. The reactivities of the phenylboronic acids containing di‐ and tri‐fluoro substituents with α‐pyridyl bromide were investigated in different catalyst systems. Unsuccessful results were observed in the Pd/C and PPh₃ catalyst system due to phenylboronic acid containing electron‐withdrawing F atom(s). For the catalyst system of Pd(OAc)₂/PPh₃, the reactions gave moderate yields of 55% –80%, meanwhile, affording 10% –20% of dimerisation (self‐coupling) by‐products, but trace products were obtained in coupling with 2,4‐difluorophenylboronic acids because of steric hinderance. Pd(PPh₃)₄ was more reactive for boronic acids with sterically hindering F atom(s), and the coupling reactions gave good yields of 90% and 91% without any self‐coupling by‐product.     

Enzyme‐Mediated Preparation of (+)‐ and (−)‐β‐Irone and (+)‐ and (−)‐cis‐γ‐Irone from Irone alpha®

The (−)‐ and (+)‐β‐irones ((−)‐ and (+)‐ 2 , resp.), contaminated with ca. 7 – 9% of the (+)‐ and (−)‐trans‐α‐isomer, respectively, were obtained from racemic α‐irone via the 2,6‐trans‐epoxide (±)‐ 4 (Scheme 2). Relevant steps in the sequence were the LiAlH₄ reduction of the latter, to provide the diastereoisomeric‐4,5‐dihydro‐5‐hydroxy‐trans‐α‐irols (±)‐ 6 and (±)‐ 7 , resolved into the enantiomers by lipase‐PS‐mediated acetylation with vinyl acetate. The enantiomerically pure allylic acetate esters (+)‐ and (−)‐ 8 and (+)‐ and (−)‐ 9 , upon treatment with POCl₃/pyridine, were converted to the β‐irol acetate derivatives (+)‐ and (−)‐ 10 , and (+)‐ and (−)‐ 11 , respectively, eventually providing the desired ketones (+)‐ and (−)‐ 2 by base hydrolysis and MnO₂ oxidation. The 2,6‐cis‐epoxide (±)‐ 5 provided the 4,5‐dihydro‐4‐hydroxy‐cis‐α‐irols (±)‐ 13 and (±)‐ 14 in a 3 : 1 mixture with the isomeric 5‐hydroxy derivatives (±)‐ 15 and (±)‐ 16 on hydride treatment (Scheme 1). The POCl₃/pyridine treatment of the enantiomerically pure allylic acetate esters, obtained by enzymic resolution of (±)‐ 13 and (±)‐ 14 , provided enantiomerically pure cis‐α‐irol acetate esters, from which ketones (+)‐ and (−)‐ 22 were prepared (Scheme 4). The same materials were obtained from the (9S) alcohols (+)‐ 13 and (−)‐ 14 , treated first with MnO₂, then with POCl₃/pyridine (Scheme 4). Conversely, the dehydration with POCl₃/pyridine of the enantiomerically pure 2,6‐cis‐5‐hydroxy derivatives obtained from (±)‐ 15 and (±)‐ 16 gave rise to a mixture in which the γ‐irol acetates 25a and 25b and 26a and 26b prevailed over the α‐ and β‐isomers (Scheme 5). The (+)‐ and (−)‐cis‐γ‐irones ((+)‐ and (−)‐ 3 , resp.) were obtained from the latter mixture by a sequence involving as the key step the photochemical isomerization of the α‐double bond to the γ‐double bond. External panel olfactory evaluation assigned to (+)‐β‐irone ((+)‐ 2 ) and to (−)‐cis‐γ‐irone ((−)‐ 3 ) the strongest character and the possibility to be used as dry‐down note.     

Synthesis of (P)‐ and (M)‐6,7‐Bis[(diphenylphosphanyl)methyl]‐8,12‐diphenylbenzo[a]heptalenes – Potential Ligands for Homogeneous Asymmetric Catalysis

The title bis(phosphane) ligands have been prepared starting from optically pure diisopropyl (P)‐ and (M)‐8,12‐diphenylbenzo[a]heptalene‐6,7‐dicarboxylates ((P)‐ 1b and (M)‐ 1b ) that had been obtained by HPLC separation of rac‐ 1b on a semi‐preparative Chiralcel OD column. Reduction of (P)‐ 1b and (M)‐ 1b with diisobutylaluminum hydride (DIBAH) gave optically pure (P)‐ and (M)‐dimethanols 3 (Scheme 6 and Fig. 5). Unfortunately, the almost quantitative chlorination of rac‐ 3 with PCl₅ in CHCl₃ at −60° led with (M)‐ 3 to nearly complete loss of optical integrity. However, mesylate formation of (P)‐ 3 , followed by phosphanylation with LiP(BH₃)Ph₂ gave (P)‐ 6 with only a small loss of optical activity. Optically pure (P)‐ 6 was obtained by crystallization from Et₂O/hexane, which removed the nearly insoluble rac‐ 6 . The pure bis(phosphane) ligands (P)‐ 2 and (M)‐ 2 can be liberated quantitatively from 6 by warming 6 in toluene in the presence of 1,4‐diazabicyclo[2.2.2]octane (DABCO). First Rh^I‐catalyzed asymmetric hydrogenation reactions of (Z)‐α‐(acetamido)cinnamic acid ((Z)‐ 14 ) in the presence of (P)‐ 2 led to (R)‐N‐acetylphenylalanin ((R)‐ 15 ) in optical purities up to 77% (see Table 1).     

1,8‐Bis[(dimethoxy)phosphino]naphthalene: A New Bis‐phosphonite Ligand with a Rigid C3‐Backbone and Unexpected Reaction Chemistry

1,8‐Bis[(diethylamino)phosphino]naphthalene ( 1 ) reacted with dry methanol in dichloromethane to form the new bis‐phosphonite ligand 1,8‐bis[(dimethoxy)phosphino]naphthalene (dmeopn, 2 ). By oxidation of 2 with H₂O₂ · (H₂N)₂C(:O) the corresponding bis‐phosphonate, 1,8‐bis[(dimethoxy)phosphoryl]naphthalene ( 3 ), was obtained quantitatively. Reaction of 3 with phosphorus trichloride unexpectedly furnished a 2.4 : 1 mixture of the bis‐phosphonate anhydrides rac‐ and meso‐1,3‐dimethoxy‐1,3‐dioxo‐2,3‐dihydro‐1,3‐diphospha‐2‐oxaphenalene (rac‐ 4 and meso‐ 4 ) from which rac‐ 4 could be fractionally crystallised. The bis‐phosphonite 2 behaved as a normal bidentate chelate ligand towards Mo⁰ and Pd^II, and furnished the complexes [(dmeopn)Mo(CO)₄] ( 5 ) and [(dmeopn)PdCl₂] ( 6 ) when treated with [(nor)Mo(CO)₄] or [(cod)PdCl₂] (nor = norbornadiene, cod = cycloocta‐1,8‐diene). Attempts to prepare 1,8‐diphosphinonaphthalene ( 7 ) by reducing 2 or 3 with LiAlH₄ or LiAlH₄/TMSCl (1 : 1) (TMSCl = trimethyl chlorosilane) in THF led to inseparable mixtures of phosphorus‐containing products. Compounds 2 – 6 were characterised by ¹H‐, ¹³C‐, and ³¹P‐NMR spectroscopy, IR spectroscopy, mass spectrometry and elemental analysis. X‐ray crystal structure analyses were carried out for the bis‐phosphonate anhydride rac‐ 4 and the palladium(II) complex 6 . The geometry of compound rac‐ 4 , in which the phosphorus atoms are connected by an oxygen atom, reveals a relief of strain from the bis‐phosphine 1 , whereas the 1,8‐P,P′‐naphthalenediyl group in 6 is surprisingly distorted; the P atoms are displaced from the naphthalene best plane by –46.7 and 54.5 pm.     

Reactions of 2‐amino‐3‐cyano‐4,5,6,7‐tetrahydrobenzo[b]thiophene and 2‐amino‐3‐cyano‐4,7‐diphenyl‐5‐methyl‐4H‐pyrano[2,3‐c] pyrazole with phenylisocyanate,carbon disulfide,and thiourea

2‐Amino‐3‐cyano‐4,5,6,7‐tetrahydrobenzo[b]thiophene 1a or 2‐amino‐3‐cyano‐4,7‐di‐ phenyl‐5‐methyl‐4H‐pyrano[2,3‐c]pyrazole 2a reacted with phenylisocyanate in dry pyridine to give 2‐(3‐phenylureido)‐3‐cyanobenzo[b]thiophene 1b or 2‐disubstituted amino‐3‐cyanopyranopyrazole 2b derivative. However, when 1a and 2a were refluxed with carbon disulfide in 10% ethanolic sodium hydroxide solution, they afforded the thieno[2,3‐d]pyrimidin‐2,4‐dithione derivative 5 in the former case, 2,4‐dicyano‐1,3‐bis(dithio carboxamino)cyclobuta‐1,3‐ diene 6 and pyrazolopyranopyrido[2,3‐d]pyrimidin‐ 2,4‐dithione derivative 7 in the latter one. Treatment of 2a with thiourea in refluxing ethanol in the presence of potassium carbonate gave 2,2′‐dithiobispyrimidine derivative 9 (major) in addition to pyranopyrazole derivative 10 and 2,2′‐dithiobis ethoxypyrimidine derivative 11 in minor amounts. The structures of all products were evidenced by microanalytical and spectral data. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:6–11, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20070     

Pd‐Catalyzed Synthesis of α‐Aryl Vinylphosphonates via Suzuki Arylation of α‐Phosphonovinyl Nonaflates

The first palladium‐catalyzed method for the arylation of α‐phosphonovinyl nonaflates is described. Using a catalyst comprised of Pd(OAc)₂ and SPhos, terminal and internal α‐aryl vinylphosphonates could be efficiently accessed under mild conditions. The reaction features a broad coupling partner scope and tolerates many functional groups.     

New P‐ligands: The aromaticity and reactivity of 2,4,6‐trialkylphenylphospholes

A further member of 2,4,6‐trialkyl‐phenyl‐phos‐pholes, the ditertbutylmethylphenyl derivative ( 1c ) was characterized by Bird index and by the sum of angles at the phosphorus atom to describe the flattening of the P‐pyramid. Both numbers suggested a slight aromaticity. The reaction of arylphospholes with phosphorus tribromide was extended to phosphole 1c leading this occasion, after further steps, to the mixture of 3‐ and 2‐substituted products ( 3c‐1 and 3c‐2 , respectively). A triisopropylphenyl‐2H‐phosphole ( 4 ) formed by sigmatropic rearrangement was utilized in the preparation of new 1‐phosphanorbornene derivatives, such as sulfide 6 and hemi‐oxides 8‐1 and 8‐2 . Further oxidation of the latter species ( 8‐1 and 8‐2 ) led to the decomposition of the dimeric structure ( 11 ). 4 could also be trapped by benzaldehyde to afford the oxaphosphanorbornene ( 10 ) as one diastereomer. Finally, the reversible formation of 2H‐phosphole 4 from 1H‐phosphole 1a at 150°C was proved. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:104–222, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20077     

Preparations of Saturated N‐P‐N Type Secondary Phosphine Oxides and their Applications in Cross‐Coupling Reactions

A series of cyclohexane‐1,2‐diamine ( 3a – 3d ) and benzene‐1,2‐diamine derivatives ( 3e – 3h ) were pre‐ pared. Followed by hydrolysis, the reaction of 3a – 3c with PCl₃ successfully led to the formation of cor‐ responding metastable saturated heteroatom‐substituted secondary phosphine oxides (HASPO 4a – 4c ), a tautomer of the saturated heteroatom‐substituted phosphinous acid (HAPA). Whereas ambient‐stable diamine‐coordinated palladium complexes were obtained, HAPA‐coordinated palladium complexes were not successfully synthesized. The molecular structures of HASPO 4c , Pd(OAc)₂(3a) , PdBr₂(3b) and Pd(OAc)₂(3c) and [Cu(NO₃)(3d)⁺][NO₃ ^? ] were determined by single‐crystal X‐ray diffraction method. Catalysis of in‐situ Suzuki‐Miyaura cross‐coupling reactions for aryl bromides and phenylboronic acid using diamine 3a as ancillary ligand showed that the optimized reaction condition at 60 °C is the combination of 2 mmol % 3a /3.0 mmol KOH/1.0 mL 1,4‐dioxane/1 mmol % Pd(OAc)₂. Moreover, moderate reactivity was observed when using aryl chlorides as substrates (supporting infor‐ mation). When diamine 3d was employed in Heck reaction, good tolerance of functional groups of aryl bromides were observed while using 4‐bromoanisole and styrene as substrates. The optimized condi‐ tion for Heck reaction at 100 °C is 3 mmol % 3d /3.0 mmol CsF/1.0 mL toluene/3 mmol % Pd(OAc)₂. In general, cyclohexane‐1,2‐diamine derivatives exhibited better catalytic properties than those of benzene‐1,2‐diamines.     

Oxazoline chemistry part III. Synthesis and characterisation of [2‐(2′‐anilinyl)‐2‐oxazolines] and some related compounds

The syntheses and characterisation of a series of chiral and achiral 2‐(aminophenyl)‐2‐oxazolines and some related compounds is reported. All of the derivatives have been produced by a one‐step procedure involving the treatment of isatoic anhydride (i.e. [2H]‐3, 1‐benzoxazine‐[1H‐2,4‐dione: 1 ) or its 5‐chloro analogue with a slight excess of appropriate amino‐alcohols. In most cases, anhydrous ZnCl₂ is shown to be an effective Lewis acid catalyst for this reaction at reflux temperature in high boiling aromatic solvents (PhCl or PhMe). Oxazolines have been readily formed using rac‐2‐amino‐1‐butanol, (S)‐phenylglycinol, 2‐methyl‐2‐amino‐1‐propanol and (1S,2R) or (IR,2S)‐cis‐ 1 ‐amino‐2‐indanol; yields range from 85% to 22%. The use of aminoalcohols such as 2‐ethanolamine, (±)‐2‐amino‐1‐phenyl‐1‐propanol or 3‐amino‐1‐propanol (to give the corresponding 4,5‐dihydro‐1,3‐oxazine) results in poor yields. The use of other Lewis acid catalysts (silicic acid, Cd(acac)₂·2H₂O, CuCl₂·2H₂O, InCl₃) or higher temperatures did not improve the yields with these latter two substrates. Benzoxazoles and N‐substituted benzoxazoles can also be obtained in reasonable yields from 1 using 2‐aminophenol (36%) or 2‐amino‐3‐hydroxypyridine (45%).     

新型联吡啶配体P-Phos在钯催化胺偶联反应中的应用

P-Phos [2,2′6,6′-四甲氧基吡啶-4,4′-二(二苯基膦)-3,3′-联吡啶]是一类对空气稳定的杂环磷配体。本文以较简单的方法合成了rac-P-Phos配体,并用IR、1H NMR、13C NMR和元素分析等方法进行了表征。首次将P-Phos配体用于催化卤代芳烃和胺的偶联反应中。通过对碱、溶剂和催化剂用量等的筛选,确立了最优化的反应条件。配体对溴代芳烃的催化效果很好,对具有吸电子存在的氯代芳烃,特别是氯代吡啶同样得到了令人满意的结果,分离产率高达97％。催化剂对水和空气的稳定性很好,对胺偶联反应的催化效果很理想,因此是一种有应用前景的催化剂。     

Synthesis of 8‐Oxoberbines and Related Benzolactams by Pd(OAc)2‐Catalyzed Direct Aromatic Carbonylation

A variety of alkoxy‐substituted benzolactams with a berbine or yohimbane skeleton were prepared from 1‐benzyl‐1,2,3,4‐tetrahydroisoquinolines or 1‐benzyl‐1,2,3,4‐tetrahydro‐β‐carbolines by a phosphine‐free Pd(II)‐catalyzed direct aromatic carbonylation in a Pd(OAc)₂‐Cu(OAc)₂ catalytic system. The site selectivity was compared with that of the carbonylation with Pd(OAc)₂ or Pd(OAc)₂·2 PPh₃, respectively.     

Four N7‐benzyl‐substituted 4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐diones as ethanol hemisolvates: similar molecular constitutions but different crystal structures

3‐tert‐Butyl‐7‐(4‐chlorobenzyl)‐4′,4′‐dimethyl‐1‐phenyl‐4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐dione ethanol hemisolvate, C₃₀H₃₄ClN₃O₂·0.5C₂H₆O, (I), its 7‐(4‐bromobenzyl)‐ analogue, C₃₀H₃₄BrN₃O₂·0.5C₂H₆O, (II), and its 7‐(4‐methylbenzyl)‐ analogue, C₃₁H₃₇N₃O₂·0.5C₂H₆O, (III), are isomorphous, with the ethanol component disordered across a twofold rotation axis in the space group C2/c. In the corresponding 7‐[4‐(trifluoromethyl)benzyl]‐ compound, C₃₁H₃₄F₃N₃O₂·0.5C₂H₆O, (IV), the ethanol component is disordered across a centre of inversion in the space group P. In each of (I)–(IV), the reduced pyridine ring adopts a half‐chair conformation. The heterocyclic components in (I)–(III) are linked into centrosymmetric dimers by a single C—H...π interaction, with the half‐occupancy ethanol component linked to the dimer by a combination of C—H...O and O—H...π(arene) hydrogen bonds. The heterocyclic molecules in (IV) are linked into chains of centrosymmetric rings by C—H...O and C—H...π hydrogen bonds, again with the half‐occupancy ethanol component pendent from the chain. The significance of this study lies in the isomorphism of the related derivatives (I)–(III), in the stoichiometric hemisolvation by ethanol, where the disordered solvent molecule is linked to the heterocyclic component by a two‐point linkage, and in the differences between the crystal structures of (I)–(III) and that of (IV).     

Diastereoselective Electrophilic Amination of Chiral 1‐Benzoyl‐2,3,5,6‐tetrahydro‐3‐methyl‐2‐(1‐methylethyl)pyrimidin‐4(1H)‐one for the Asymmetric Syntheses of α‐Substituted α,β‐Diaminopropanoic Acids

The chiral compounds (R)‐ and (S)‐1‐benzoyl‐2,3,5,6‐tetrahydro‐3‐methyl‐2‐(1‐methylethyl)pyrimidin‐4(1H)‐one ((R)‐ and (S)‐ 1 ), derived from (R)‐ and (S)‐asparagine, respectively, were used as convenient starting materials for the preparation of the enantiomerically pure α‐alkylated (alkyl=Me, Et, Bn) α,β‐diamino acids (R)‐ and (S)‐ 11 – 13 . The chiral lithium enolates of (R)‐ and (S)‐ 1 were first alkylated, and the resulting diasteroisomeric products 5 – 7 were aminated with ‘di(tert‐butyl) azodicarboxylate’ (DBAD), giving rise to the diastereoisomerically pure (≥98%) compounds 8 – 10 . The target compounds (R)‐ and (S)‐ 11 – 13 could then be obtained in good yields and high purities by a hydrolysis/hydrogenolysis/hydrolysis sequence.