A mechanistic study on the intramolecular ionic Diels-Alder reaction of 2-methyl-3,9,11-tridecatriene-2-ol and 2,11-dimethyl-1,3,9,11-dodecatetraene

Intramolecular ionic Diels-Alder reaction of 2-methyl-3,9,11-tridecatriene-2-ol (1) was studied under acidic conditions. Treatment of 2-methyl-3,9,11-tridecatriene-2-ol (1) with trifluoromethanesulfonic acid yielded 7-methyl-8-isopropenyl-1,2,3,4,4aR^∗,7R^∗,8R^∗,8aS^∗-octahydronaphthalene (4) and (1Z)-1-((E)-but-2-enylidene)-2-(2-methylpropenyl)cyclohexane (5) through regioselective intramolecular ionic Diels-Alder reaction. The reaction appeared to proceed partly through a stepwise mechanism involving a carbocation intermediate. However, a concerted pathway rather than a stepwise one is suggested to be involved in the acid-catalyzed intramolecular Diels-Alder reaction of 2,11-dimethyl-1,3,9,11-dodecatetraene (13).     

Application of chiral tetrahydropentalene ligands in rhodium-catalyzed 1,4-addition of (E)-2-phenylethenyl- and (Z)-propenylboronic acids to enones

Chiral tetrahydropentalenes (3aR,6aR)-1 have been prepared and used as ligands in the Rh-catalyzed 1,4-addition of 1-alkenylboronic acids to cyclic enones 5. It has been discovered that the stereochemistry of the reaction was controlled by the steric properties of the aryl groups in 1 rather than their electronic nature. In the vinylation with (E)-2-phenylethenylboronic acid 5, ligands (3aR,6aR)-1 provided enantioselectivity up to 87% ee and gave high yields of ethenylketones 6 in the presence of 1 (6.6 mol %). The configuration of all ketone products obtained with (3aR,6aR)-1 is (S). Rh-catalyzed reaction of cyclopentenone 4a and (Z)-propenylboronic acid 7 in the presence of ligands (3aR,6aR)-1 yielded at 50 °C an inseparable mixture of (Z)- and (E)-ketones 8 with (Z)-8 as the major product and both in only moderate enantiomeric excess.     

Pheromone synthesis. Part 250: Determination of the stereostructure of CH503, a sex pheromone of male Drosophila melanogaster,as (3R,11Z,19Z)-3-acetoxy-11,19-octacosadien-1-ol by synthesis and chromatographic analysis of its eight isomers

All the eight stereoisomers of 3-acetoxy-11,19-octacosadien-1-ol (1), the male sex pheromone (CH503) of Drosophila melanogaster, were synthesized from two acetylenic starting materials and the enantiomers of 3,4-epoxy-1-butanol PMB ether. Complete separation of the eight isomers of 1 by reversed phase HPLC at ?20 °C was achieved after their esterification with (1R,2R)-2-(2,3-anthracenedicarboximido)cyclohexanecarboxylic acid (27), and the natural CH503 was found to be (3R,11Z,19Z)-1.     

Easy access to optically active Hagemann's esters

The synthesis of optically active Hagemann's esters was investigated. The starting materials in this approach were enamino esters (R,Z)-8, prepared through the condensation of keto ester 6 with (R)-1-phenylethylamine 7. Michael addition reaction of the enamino esters (R,Z)-8 with methyl vinyl ketone gave the expected adducts 10 with good e.e.s of 93–96%. Subsequent annulation of the adducts furnished optically active Hagemann's esters.     

Reactions of a hydrido(hydrosilylene)tungsten complex with oxiranes

Reactivity of a hydrido(hydrosilylene)tungsten complex, Cp¹(CO)₂(H)WSi(H)[C(SiMe₃)₃] (1), toward oxiranes was investigated. Treatment of 1 with racemic mono-substituted oxiranes with a substituent R (R = Ph, vinyl, ^tBu, or ⁿBu) at room temperature produced dihydrido(vinyloxysilyl)tungsten complexes, (E)- and/or (Z)-Cp¹(CO)₂(H)₂W{Si(H)(OCHCHR)[C(SiMe₃)₃]} [(E/Z)-2: R = Ph, (E)-3: R = vinyl, (E)-4: R = ^tBu, (E/Z)-5: R = ⁿBu] in high yields via regioselective ring-opening of oxiranes. When the substituent R on oxirane was relatively large, (E)-isomers (2, 3, and 4) were obtained predominantly (87–97%), while the substituent was a relatively small ⁿBu group, an approximately 1:1 mixture of (E)- and (Z)-isomers [(E/Z)-5] was obtained. Reaction of 1 with 2,2-dimethyloxirane afforded the corresponding complex, Cp¹(CO)₂(H)₂W{Si(H)(OCHCMe₂)[C(SiMe₃)₃]} (6), quantitatively. A reaction mechanism is also discussed.     

Regio- and stereoselective cycloadditions of (1Z,4R,5R)-1-arylmethylidene-4-benzoylamino-3-oxo-5-phenylpyrazolidin-1-ium-2-ides to methyl methacrylate

[3+2] Cycloadditions of (1Z,4R^∗,5R^∗)-1-arylmethylidene-4-benzoylamino-3-oxo-5-phenylpyrazolidin-1-ium-2-ides 1a-e to methyl methacrylate gave the 1-CO₂Me regioisomers 3/3′, exclusively, in 1-67% yields. Stereocontrol was dependent on the ortho-substituents at the 1′-aryl group in dipole 1: ortho-unsubstituted dipoles 1a-c gave the major (1R^∗,3R^∗,5R^∗,6R^∗)-isomers 3a-c, whilst ortho-disubstituted dipoles gave the major (1R^∗,3S^∗,5R^∗,6R^∗)-isomers 3′d,e. The structures of cycloadducts were determined by NMR and X-ray diffraction.     

Further studies on the taumerization of the hydrido (alkynyl) cluster Ru3Pt(μ-H) {μ4-ν2-C ≡ C1Bu} (CO)9(L2) to the vinylidene cluster Ru3Pt{μ4-ν2-C ≡ C(H)tBu} (CO)9(L2): X-ray structures of Ru3Pt(μ-H){μ4-ν2-C = C(H)tBu} (CO)9(L2); L2 = dppet,dppp, andS,S-dppb

The first order rate constants for the tautomerization of the hydrio(alkynyl) clusters Ru₃Pt(μ-H){μ₄-ν²-C ≡ C¹Bu}(CO)₉(L₂);1a: L₂ = dppe,1b; L₂ = dppet,1c; L₂ = dppp and1d; L₂ =S,S-dppb to the corresponding vinylidene clusters Ru₃Pt{μ₄-ν²-C = C(H)^tBu}(CO)₉(L₂)2 have been measured, and they follow the orser1d <1a <1b ～1c. The reactions involving1a and1d exhibit an inverse kinetic deuterium isotope effect. The structures of1b, 2b, 2c, and2d were determined by X-ray crystallography, and are compared with those of1a and2a which have been previously reported. Crystal data for1b, space groupPbca,a = 13.338(4) Å,b = 17.771(6) Å,c = 36.092(8) Å,Z = 8,R(R _w) = 0.059(0.058) for 2342 absorption corrected, observed data; for2b, space group P2₁/n,a = 10.566(2) Å,b = 20.234(5) Å,c = 20.270(3) Å,β = 96.11(1)°,Z = 4,R(R _w) = 0.043(0.053) for 5865 absorption corrected, observed data; for2c, space group P2₁/n,a = 14.211(5) Å,b = 19.534(2) Å,c = 15.870(2) Å,β = 100.81(2)°,Z = 4,R(R _w) = 0.055(0.031) for 6566 absorption corrected, observed data: for2d, space group P2₁2₁2₁,a = 12.309(4) Å,b = 19.047(6) Å,c = 19.206(4) Å,Z = 4,R(R _w) = 0.055(0.053) fpr 2151 absorption corrected, observed data. The fluxional behavior of1d and1e (which consists of two interconverting isomers) has been examined by variable temperature¹³C NMR spectroscopy and by³¹P EXSY.     

Synthesis of enantiomerically pure (Z)-(2′R)-1-O-(2′-methoxyhexadec-4′-enyl)-sn-glycerol present in the liver oil of cartilaginous fish

Synthesis of enantiopure (Z)-(2′R)-1-O-(2′-methoxyhexadec-4′-enyl)-sn-glycerol 1, the principal methoxylated glyceryl ether found in Nature, is described by a highly convergent five-step process taking place in 27% overall yield. The synthesis is based on an ether bond formation between the chiral synthon (R)-2,3-O-isopropylidene-sn-glycerol and (Z)-(R)-1-chlorohexadec-4-en-2-ol employing ground potassium hydroxide and tetra-n-butylammonium bromide as a catalyst under solvent free conditions.     

The synthesis of the insect pheromone (2S,3R,7R)-3,7-dimethyltridec-2-yl acetate from racemic 3,4-dimethyl-γ-butyrolactone by diastereoselective chiral resolution

The insect pheromone (2S,3R,7R)-3,7-dimethyltridec-2-yl acetate 1-Ac was prepared from diastereomerically enriched (2S¹,3R¹,7R)-1, which in turn was obtained by the coupling of racemic 3,4-dimethyl-γ-butyrolactone with (7S)-2-methyloctyllithium, followed by a Wolff–Kishner reduction of the resulting ketone. Conversion of (2S¹,3R¹,7R)-1 to the corresponding alkyl hydrogen phthalate and diastereomer salt formation with (S)-PhCHMeNH₂ provided after several crystallizations individual diastereomer, which was later transformed into target 1-Ac after hydrolysis and acylation.     

Solid-state conformation of diastereomeric -Pro-Pro-(Aib)4 sequences

The crystal structures of two diastereomeric -Pro-Pro-(Aib)₄- sequences, Cbz-l-Pro-l-Pro-(Aib)₄-OMe (1) and Cbz-d-Pro-l-Pro-(Aib)₄-OMe (2), have been determined by X-ray crystallographic analysis. The crystals of the two compounds were characterized by the following parameters: (1) monoclinic, P2₁, a=10.543 Å, b=8.103 Å, c=22.642 Å, β=97.679, Z=2, R₁=0.104, and R_w=0.327; (2) orthorhombic, P2₁2₁2₁, a=10.470 Å, b=10.953 Å, c=32.405 Å, Z=4, R₁=0.040, and R_w=0.046. In the asymmetric unit of 1, the homochiral l-Pro¹-l-Pro² adopts a polyproline II structure, which induces a left-handed (M) 3₁₀-helical structure in the following -(Aib)₄- sequence. The preferred conformation of diastereomeric 2, which contains heterochiral d-Pro¹-l-Pro² segments, was similar to that of 1 with differences at the N-terminal d-Pro residue.     

Monomeric five-coordinate rhenium diazenido and hydrazido complexes with aromatic thiolate ligands: X-ray structures of [Re(NNC6H4-Br)2(SC6H3-2,5-Me2)(PPh3)2] and [ReO(NNMePh)(SPh)3], and of the synthetic precursor [Re(NNC6H4-4-Br)2Cl(PPh3)2]

Reaction of [ReOCl₃(PPh₃)₂] with bromophenylhydrazine in methanol yields [ReCl(N₂C₆H₄Br)₂(PPh₃)₂] (1). Complex 1 reacts with arylthiolates to give mixtures of [Re(SAr)(N₂C₆H₄Br)₂(PPh₃)₂] (2) and [Re₂(SAr)₇(NNR)₂]⁻. Complexes 1 and 2 display trigonal bipyramidal geometries with the phosphine ligands occupying the axial sites. A significant feature of the structures is the nonequivalence of the rhenium-diazenido moieties, such that for 1 the ReN(1) and N(1)N(2) distances are 1.80(2) and 1.24(3) Å, while ReN(3) and N(3)N(4) are 1.73(2) and 1.32(3) Å, and for 2 the ReN distances are 1.73(1) and 1.80(2)° with corresponding NN distances of 1.32(2) and 1.25(2) Å. Reaction of (PPh₄)[ReO(SPh)₄] (3) with unsymmetrically disubstituted hydrazines affords complexes of the type [ReO(SPh)₃(NMRR′)] (R = Me, R′ = Ph for 4). Complexes 3 and 4 display distorted square pyramidal geometries with the oxo groups apical. The significant feature of the structure of 4 is the nonlinear ReN(1)N(2) linkage, exhibiting an angle of 145.6(10)°. The angle does not appear to correlate with a significant contribution from a valence form with sp² hybridization at the α-nitrogen. Crystal data: 1: monoclinic space group, P2₁/n, a = 12.216(2) Å, b = 19.098(2) Å, c = 20.257(4) Å, β = 106.20(1)°, V = 4538.3(8) ų to give Z = 4; structure solution and refinement based on 1905 reflections converged at R = 0.070. 2: monoclinic space group P2₁/n, a = 14.393(2) Å, b = 18.842(3) Å, c = 20.717(4)Å, β = 110.26(1)°, V = 5270.5(8) ų to give Z = 4 for D = 1.53 g cm⁻¹; structure solution and refinement based on 4249 reflections to give R = 0.070. 3: monoclinic space group P2₁/n, a = 12.531(2) Å, b = 24.577(4) Å, c = 16.922(3) Å, β = 99.06(1)°, V = 5146.2(9) ų, D = 1.36 g cm⁻³ for Z = 4, 2912 reflections, R = 0.050. 4: monoclinic space group p2₁/n, a = 16.137(2) Å, b = 9.863(2) Å, c = 16.668(2) Å, β = 111.12(1)°, V = 2474.7(6) ų, D = 1.74 g cm⁻³ for Z = 4, 2940 reflections, R = 0.066.     

Synthesis of the enantiomers of (3Z,9Z)-cis-6,7-epoxy-3,9-octadecadiene,one of the major components of the sex pheromone of Ectropis oblique Prout

Both enantiomers of (3Z,9Z)-cis-6,7-epoxy-3,9-octadecadiene, one of which is the major component of the sex pheromone of Ectropis oblique Prout, were synthesized in 23% overall yield for the (?)-(6S,7R)-enantiomer and 18% yield for the (+)-(6R,7S)-isomer. This protocol uses a sequential regioselective ring-opening strategy and provides a convenient and reliable access to other structurally related insect sex pheromones. Preliminary biological studies revealed that (?)-(6S,7R)-2a was roughly as active as the natural pheromone, while racemic (±)-2 was less bioactive and (+)-2b was much less bioactive.     

First total synthesis of (−)-aplyolide A

The first total synthesis of (−)-aplyolide A², (16S)-methyloxacyclohexadeca-(5Z,8Z,11Z,14Z)-tetraen-2-one, 1 is reported. The synthesis is based on three consecutive couplings of terminal alkynes with propargylic halides and proves the absolute configuration of the stereogenic center of the natural product.     

Unexpected cleavage of the N-N bond in the reactions of 3-pyrazolidinone-1-azomethine imines with HCN

Treatment of (1Z,4R^∗,5R^∗)-1-arylmethylidene-4-benzamido-5-phenylpyrazolidin-3-one 1-azomethine imines 4a-d with potassium cyanide in the presence of acetic acid resulted in addition of HCN to the exocyclic CN double bond followed by β-eliminative N-N single bond cleavage (ring opening) to give the N-[(1R^∗,2R^∗)-3-amino-2-benzamido-3-oxo-1-phenylpropyl]benzimidoyl cyanides 6a-d in 28-85% yields. Reaction of dipole 4e with HCN furnished stable intermediate, (1′S^∗,4R^∗,5R^∗)-4-benzamido-1-[cyano(mesityl)methyl]-5-phenylpyrazolidin-3-one (5e), in 76% yield. The structure of compound 6c was determined by X-ray diffraction.     

Synthesis of trioxilin B3

Both C(10) diastereomers of trioxilin B₃, presumed to be a mixture of 10(R/S), 11(R), 12(R)-trihydroxyeicosa-5(Z), 8(Z), 14(Z)-trienoic acids, were prepared from a carbohydrate derived precursor by Wittig homologation and Mitsunobu inversion.     

2-Cyano-2-indolylpropanoic acid as a chiral derivatizing agent for the absolute configuration assignment of secondary alcohols and primary amines by 1H NMR and VCD

A convenient approach for the absolute configuration assignment of secondary alcohols in the (8R,1′R,2′S,5′R)-15,25, (8S,1′R,2′S,5′R)-15,25, (8R,1′R)-21–24, and (8S,1′R)-21–24 ester series, and of primary amines in the (8R,1′R)-32–37 and (8S,1′R)-32–37 amide series, by means of ¹H NMR and VCD spectroscopy, using 2-cyano-2-indolylpropanoic acid as a chiral derivatizing agent is presented. DFT calculations were carried out to demonstrate the anisotropic effect of the indole skeleton on the chiral alcohol or the amine fragment. Vibrational circular dichroism (VCD) measurements of the above series indicated a VCD bisignated couplet resulting from the interaction of the ester carbonyl group and the CN group. The absolute configuration assignments were further tested by X-ray diffraction analysis.     

Synthesis and absolute configuration of two diastereoisomeric (1R,2S,3R)-and (1S,2S,3R)-2-amino-1-(2-furyl)-1,3-butandiols

The synthesis of (1R, 2S, 3R) and (1S, 2S, 3R)-2-(N-benzoylamino)-1-(2-furyl)-1, 3-butandiols (15) and (16) from D-threonine is described. The assignment of absolute configuration of the newly formed asymmetric center at C-1 was based on the ¹H-NMR spectra of O-isopropylidene derivatives 17 and 18.     

Chiral building-blocks by chemoenzymatic desymmetrization of 2-ethyl-1,3-propanediol for the preparation of biologically active natural products

2-Ethyl-1,3-propanediol 1 and its related di-O-acetate 2 were desymmetrized by partial chemoenzymatic acetylation and deacetylation, by Pseudomonas fluorescens lipase (Amano P.; PFL), to (R)-1-O-acetyl-2-ethyl-1,3-propanediol 3. On treatment of 3 with I₂/Ph₃P/imidazole the related (S)-1-O-acetyl-2-ethyl-3-iodopropanol 4 was obtained and transformed into the corresponding triphenylphosphonium salt 5. Reaction of [(S)-3-acetoxy-2-ethylpropylidene]triphenylphosphorane 6, prepared from 5, with 2,3:4,5-di-O-isopropylidene-β-d-arabino-hexos-2-ulopyranose 7 gave (Z)-3-C-acetoxymethyl-1,2,3,4,5-pentadeoxy-6,7:8,9-di-O-isopropylidene-β-d-manno-dec-4-ene-6-ulo-6,10-pyranose 8 which was hydrogenated to 9 and subsequently deacylated to 10. Treatment of 10 with Me₂CO/H⁺ caused a rearrangement to (3R,4R,5S,6R,9R)-9-ethyl-5-hydroxy-3,4-isopropylidenedioxy-1,7-dioxaspiro[5.5]undecane 11, which closely matched the skeleton of the talaromycins.     

Stereospecific synthesis and hydrolysis of optically active diaryl(acylamino)(acyloxy)spiro-λ4-sulfanes and related cyclic diaryl(acylamino)sulfonium salts

The stereospecific synthesis of diaryl(acylamino)(acyloxy)spiro-λ⁴-sulfanes (S)-(+)-2, (R)-(+)-5, (S)-(+)-8, and their conversion into related diaryl(acylamino)sulfonium tetrafluoroborates (R)-(+)-3, (S)-(+)-6, (R)-(+)-9, respectively, is described. The enantiomers of spiro-λ⁴-sulfanes (S)-(+)-2, (R)-(+)-5 and (S)-(+)-8 were prepared by dehydration of the corresponding optically active sulfoxide–carboxylic acids (R)-(+)-1, (R)-(−)-4 and (S)-(+)-7, respectively, which were obtained from the racemic forms by diastereoisomeric salt separation with homochiral organic bases. The stereomechanism of the hydrolysis reaction of spiro-λ⁴-sulfanes and sulfonium tetrafluoroborates that depends on pH, the nature of the axial heteroatom, the size of the spiro rings and carboxyl neighbouring group participation is also discussed.     

Chemo-enzymatic synthesis of the active enantiomer of the anorressant 2-benzylmorpholine

Baker's yeast reduction of (Z)-α-bromocinnamaldehyde 1 in the presence of absorbing resins allows the easy preparation of the corresponding saturated bromo-alcohol 2 in high yields and enantiomeric excess. The absolute configuration is assigned through conversion into the (R)-phenyl oxirane 3 and 1-phenyl-2-propanol 4 of (S) absolute configuration. The (R)-epoxide is transformed into 6, the pharmacologically active enantiomer of the appetite suppressant 2-benzylmorpholine, to which the (R) configuration is assigned.