Chiral synthesis of (2s,3s,7s)-3,7-dimethylpentadecan-2-yl acetate and propionate,potential sex pheromone components of the pine saw-fly neodiprion sertifer (geoff.)

A synthesis of (2S,3S,7S)-3,7-dimethylpentadecan-2-yl acetate ($\text{2}$) and propionate ($\text{3}$) is described. (2S)-2-Methyldecan-1-yl lithium ($\text{5}$) was reacted with (3S,4S)-3,4-dimethyl-γ-butyrolactone ($\text{6}$) to yield the ketoalcohol $\text{19}$ which upon Huang-Minlon reduction furnished (2S,3S,7S)-3,7-dimethylpentadecan-2-ol ($\text{1}$). Acylations gave the esters $\text{2}$ and $\text{3}$. The (2S)-2-methyldecan-1-yl lithium was obtained via asymmetric synthesis. The chiral lactone $\text{6}$ was obtained from (2S,3S)-trans-2,3-epoxybutane and dimethyl malonate.     

S)-(+)-2-(p-tolylsulfinyl)-2-buten-4-olide: an enantiomerically pure Michael acceptor for asymmetric synthesis of 3-substituted 4-butanolides. (—)-podorhizon.

A short, reliable, and practical synthesis of ($\text{S}$)-(+)-2-($\text{p}$-tolylsulfinyl)-2-buten-4-olide has been developed, and the utility of this Michael acceptor for highly enantiocontrolled synthesis of 3-substituted 4-butanolides has been demonstrated.     

Synthesis of detoxininolactone derivatives and the revised absolute stereochemistry of detoxinine

A stereospecific synthesis of acetyl-$\text{L}$-valyl-detoxininolactone has been performed and the absolute stereochemistry of detoxinine has been revised to (2$\text{S}$, 3$\text{R}$, 1′$\text{S}$)-2-(2′-carboxy-1′-hydroxyethyl)-3-hydroxypyrrolidine.     

A high yield synthesis of (±)-5,8-dimethoxy-2-α-hydroxyethyl-3,4-dihydronaphthalene,a key intermediate in anthracyclinone synthesis

The dimethoxytetralol ($\text{2}$) gives on Vilsmeier reaction the dihydronaphthaldehyde ($\text{3}$) (yield,92%), which on Grignard reaction with MeMgI affords the title compound ($\text{6}$) (yield,~100%), the reactions constituting a high yield synthesis of this important anthracyclinone intermediate.     

Stereochemical consequence in the elimination of β-hydroxyalkylsilanes: Stereoselective formation of (Z)- and (E)-alkylidene-γ-butyrolactones

Titanium(IV) chloride-mediated reaction of 4,5-dihydro-2-(trimethylsiloxy)-3-(trimethylsilyl)furan (1a) with acetaldehyde gave $\text{diastereomerically pure}$ (3S^*, 1′R^*)-4,5-dihydro-3-(1′hydroxyethyl)-3-(trimethylsilyl)-2(3$\text{H}$)furanone (2a), which afforded selectively either (Z)- or (E)-α-ethylidene-γ-butyrolactone (3a) under proper conditions. Facile isomerization of 2a into $\text{diastereomerically pure}$ (3S^*, 1′R^*)-4,5-dihydro-3-&{1′-(trimethylsiloxy)ethyl}-2(3$\text{H}$)furanone (4) suggests an intriguing stereochemical outcome from 2a to (E)-3a via an enolate of 4.     

4,6-Thioanhydro-hexopyranosides,synthesis and chemical behaviour of methyl 2-0-p-toluenesulfonyl-4,6-thioanhydro-α-d-gulopyranoside

Methyl 4-0-benzoyl-6-bromo-6-deoxy-α-D-glucopyranoside ($\text{1}$, Figure 1) was converted, via the corresponding ditosylate $\text{2}$, into methyl 2,3-di-0-p-toluenesulfonyl-4-0-benzoyl-6-S-acetyl-6-thio-α-D-glucopyranoside ($\text{3}$) by a selective nucleophilic displacement of 6-bromo-group with thioacetate. Unexpectedly, on treating the compound $\text{3}$ with an excess of sodium methoxide in benzene-methanol (1:1) at room temperature, methyl 2-0-p-toluenesulfonyl-4,6-thioanhydro-α-D-gulopyranoside ($\text{4}$) was obtained in a yield of 84%. In order to determine the structure of the relatively unstable oily product $\text{4}$, some stable crystalline derivatives ($\text{5}$, $\text{6}$ and $\text{7}$) were prepared. Detailed analysis of the ¹H-NMR-spectra (200 MHz) of $\text{6}$ and $\text{7}$ gave the conclusive evidence for the structure of $\text{4}$ A self-imposing mechanism of the clean and smooth transformation of $\text{3}$ to $\text{4}$ is proposed, involving: a) formation of $\text{9}$ (Figure 2) as a crucial intermediate and b) a highly regioselective epoxide opening in $\text{9}$ (at C-4) by an intramolecular nucleophilic attack of the mercaptide anion from C-6.     

Methylated multibridged [2n]cyclophanes. All alternate synthesis of [26](1,2,3,4,5,6) cyclophane (superphane)

A sequence of formylation followed by a carbene insertion reaction has led to the stepwise introduction of additional ethano bridges into 4,5,7,8- tetramethyl [2₂](1,4)cyclophane ($\text{1}$), providing syntheses of 5,7,8-trimethyl- [2₃](l,2,4)cyclophane ($\text{6}$), a mixture of 5,8-dimethyl[2₄(1,2,4,5)cyclophane ($\text{10}$) and 5,7-dimethyl[2₄(1,2,3,5)cyclophane ($\text{11}$, and-4-methyl[2₅](1,2,3,4,5)-cyclophane ($\text{14}$). This route to $\text{14}$ completes a formal eight-step synthesis of [2₆](1,2,3,4,5,6)cyclophane ($\text{15}$, superphane) with an overall yield of 17%. A Birch reduction of $\text{6}$ readily gave 12,15-dihydro-5,7,8-trimethyl[2₃](1,2,4)-cyclophane ($\text{7}$) in 85% yield.     

A new synthesis of N-benzoyl L-acosamine

Reaction of (2$\text{R}$,3$\text{S}$)-2,3-(cyclohexylidenedioxy)butanenitrile, derived from ethyl ($\text{S}$)-lactate, with the magnesium enolate of t-butyl acetate gave the corresponding ($\text{Z}$)-β-amino acrylate derivative, which was transformed into N-benzoyl acosamine by acetylation, stereoselective hydrogenation, acidic hydrolysis, and ring-formation followed by reduction with diisobutylaluminium hydride.     

Anomalies in the asymmetric hydroboration of olefins with the 11 adduct of (+)-α-pinene and BH3 · THF

The hydroboration of cis-2-butene and cis-3-hexene with pure diisopinocampheylborane (IPC₂BH) and monoisopinocampheylborane (IPCBH₂), both prepared from (+)-α-pinene, were studied. In contrast to IPC₂BH, which yielded R-(?)-2-butanol and R-(?)-3-hexanol in 98.4 and 94.5% optical purities, IPCBH₂ yielded S-(+)-2-butanol and S-(+)-3-hexanol in 23.6 and 19.7% optical purifies respectively. PMR examination of the methanolyzed products were utilized to establish the species present in the freshly prepared and aged $\text{1}\text{1}$ adduct from (+)-α-pinene and BH₃ · THF. The results confirm the interpretation previously advanced for the major differences realized in asymmetric hydroboration with the fresh and aged $\text{1}\text{1}$ adducts.     

Stereocontrolled synthesis of (+)-thienamycin from 3(R)-hydroxybutyric acid

The vinyloxyborane(5), prepared from (+)-$\text{S}$-phenyl-3($\text{R}$)-butanethioate, 9-BBN triflate and diisopropylethylamine, reacted with $\text{N}$-(3-benzyloxypropylidene)benzylamine to give the β-benzylamino thiol ester(6) in a moderate yield, which was efficiently converted to the optically pure thienamycin intermediate(10).     

Stereochemistry of aplidiasphingosine as proposed by the asymmetric synthesis and 13c-nmr study of sphingosine relatives

The Sharpless asymmetric epoxidation was used for the synthesis of D-$\text{erythro}$-dihydrosphingosine triacetate and (2$\text{S}$, 3$\text{S}$, 5$\text{R}$)-2-acetamino-5,9-dimethyl-8-decene-1,3-diol, whose ¹³C-NMR study coupled with biogenetic consideration enabled us to propose (2$\text{1S}$, 3$\text{S}$, 5$\text{S}$,13$\text{R}$, 14$\text{S}$)-stereochemistry for aplidiasphingosine.     

A short and stereoselective synthesis of the (±) Prelog-Djerassi lactonic acid

Reaction of meso-4-carbomethoxy-2-methylpentanal ($\text{1}$) with crotyltri-n-butyltin at ?78°C in the presence of 1 eq BF₃·OEt₂, followed by the lactonization with BF₃·OEt₂, gave 6-(1-methylallyl)-3,4,5,6-tetrahydro-3,5-dimethyl-2-pyranone ($\text{2a}$) with the correct stereochemistry (erythro, anti-Cram) in 92% yield, which was converted to the title compound ($\text{3}$) in 85% yield upon the ozonolytic cleavage of the double bond.     

Stereoselective synthesis of 3-(1-Hydroxyethyl)-2-azetidinonesfrom 3-hydroxybutyrates

Addition of dianions of 3-hydroxybutyrates to benzylideneaniline results in direct formation of $\text{trans}$$\text{S*}$-3-(l-hydroxyethyl)-1,4-diphenyl-2-azetidinone with 95% diastereoselectivity. Inversion of the configuration at Cα, gives the desired $\text{trans}$$\text{R*}$-2-azetidinone in high yield.     

A practical process for large-scale synthesis of (S)-5-hydroxy-6-trans-8,11,14-cis-eicosatetraenoic acid (5-HETE)

($\text{S}$)-5-Hydroxy-6-$\text{trans}$-8,11,14-$\text{cis}$-eicosatetraenoic acid (5-HETE) (1) and its enantiomer are readily available by a chemical synthesis from arachidonic acid which includes a chromatographic separation of diastereomeric urethanes (3) made from (±)-5-HETE methyl ester and the isocyanate 4 derived from dehydroabietylamine.     

Acyclic stereocontrol via asymmetric [2,3]-Wittig rearrangement with high enantio- and erythro-selectivity and its use in the chiral synthesis of insect pheromones

Such an asymmetric [2,3]-Wittig variant that is both highly enantio- and erythro-selective is described within the context of the chiral synthesis of the insect pheromones, (3$\text{S}$, 4$\text{S}$)-4-methyl-3-heptanol and ($\text{S}$)-4-methyl-3-heptanone.