Christian Girard

Stereoselective pig liver esterase-catalyzed hydrolysis of rigid bicyclic meso-diesters: preparation of optically pure 4,7-epoxytetra- and hexa-hydrophthalides

Abstract The bicyclic and rather rigid meso-diesters 1 - 3 have been found to be good substrates for pig liver esterase. The half-esters obtained have been converted to either one of the enantiomers of tricyclic lactones, of potential value for natural product synthesis.

A practical synthesis of 2-deoxy aldonolactones via a SmI2-mediated α-deoxygenation reaction

Abstract A one-step deoxygenation of 2-hydroxylactones or their acetates is possible using samarium diiodide as an electron-transfer reagent in conjunction with a proton source.

Enzymatic resolution of methyl 2-alkyl-2-arylacetates

Abstract Horse liver esterase, used as its inexpensive commercial acetone powder, catalyzes the selective hydrolysis of methyl 2-alkyl-2-arylacetates to afford R(−)-2-alkyl-2-arylacetic acids and S(+)-methyl 2-alkyl-2-arylacetates.

1,2-anti diastereoselective reduction of 2-alkyl-3-hydroxy-ketones via their silyl ethers

Abstract T-butyldimethylsilyl ethers of a range of acyclic 2-alkyl-3-hydroxy-ketones are reduced with lithium aluminum hydride to give with a high 1,2-anti diastereoselective induction syn,anti or anti,anti 2-alkyl-1,3-diols.

The cyclopropanation of silyl enol ethers of cisoid or labile α-ethylenic ketones. A general and rapid route to cyclobutanones and cyclopentanones.

Aus den ungesattigten Ketonen (Ia) und (Ib) entstehen die Silyl-Enolather (IIa) und (IIb), die selektiv nach Simmons-Smith (Methylenjodid-Zn/Ag) zu den Cyclopropanen (III) umgesetzt werden.

Stereocontrolled reactions induced by a thermolabile group. Synthesis of optically active 1,3-diols.

Abstract Wittig Horner-Michael reactions of phosphonates with optically active lactol 1 lead preferentially to one diastereoisomer. 2 . Force field calculations conducted on one pair of diastereoisomers 2c and 2′c predict that these isomers must exist in different conformations of similar energies. 1 H NMR data are in good agreement with these predictions. The dihydrofurans obtained by retro Diels-Alder reactions of 2 are easily transformed into optically pure 1,3-diols, precursors of R-(+)-α-lipoic acid and (−)-(1R,3R,5s)- 1,3-dimethyl −2,9-dioxabicylco [3.3.1]nonane.

Stereoselective alkylation of the lithium di-enolate of bis-2,3-carbomethoxy bicyclo[2.2.1]hept-5-ene. A convenient synthesis of mono- and disubstituted fumarate esters.

Abstract The diesters formed by a Diels-Alder reaction betweencyclopentadiene and methyle maleate or fumarate give the same lithium dienolate which is stereoselectively mono- or dialkylated. The products obtained are good precursors for substituted fumarate esters.

Regioselective SN′ allylic substitution versus 1,4-addition: Synthesis of α-substituted β,γ-unsaturated esters

The reaction of the higher order organocuprate reagents R2Cu(CN)Li2-BF3 with γ-bromo α,β-unsaturated esters gives with very high selectivity α-substituted β,γ-unsaturated esters arising from a SN′ allylic substitution. This reaction allows an easy access to α-silyl β,γ-unsaturated esters.

A general and stereoselective approach to nonactate esters and isomers: A versatile synthesis of (+)-methyl nonactate

Abstract A total synthesis of (+)-methyl nonactate from a chiral synthon obtained by enantioselective enzymatic transesterification is described. This new approach involves stereoselective reactions of aldolisation, reduction and intramolecular Michael addition and appears to be quite general since it could be applied as well to the synthesis of both enantiomers of 2- or 8- epi nonactate esters or homologues.

A novel and efficient stereoselective synthesis of the southern part of pamamycin-607

Abstract The C 1′ C 11′ portion of the antibiotic pamamycin-607 was synthesized from the enantiomerically pure hydroxy acetate 3 , readily available by enzymatic transesterification of the corresponding diol with vinylacetate. This synthesis entailed a series of stereoselective transformations: the absolute configurations of C 6′ and C 8′ were fixed by an aldol condensation followed by an anti-reduction of the resulting β-hydroxyketone. The configurations of the last two asymmetric centers C 2′ and C 3′ were controlled by a novel highly diastereoselective intramolecular cyclization catalyzed by fluoride ions.