R. Bloch

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.

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.

A general and stereoselective synthesis of (e,e)-conjugated dienes.

Abstract Cis-2,5-disubstituted-2,5-dihydrothiofene-1,1-dioxides, generated by a retro Diels-Alder reaction, lead with high stereoselectivity to (E,E)-1,4-disubstituted-1,3-dienes. The efficiency of this method is illustrated by the synthesis of two dienic insect sex pheromones.

Stereoselective reactions induced by a thermolabile group: chelation and non chelation controlled additions of organometallics to a Diels-Alder adduct of furan

Abstract The chelating ability of the bridge oxygen of lactol 2, an equivalent of the β-alkoxy γ-hydroxy aldehyde 3 , is used to induce selective diastereofacial additions of organometallics to the carbonyl group of the aldehyde.

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.

Stereoselective preparation of conjugated dienoates and dienamides. New synthesis of pellitorine and pipercide

Abstract (E) and (E,E)-conjugated dienoates and dienamides of high stereoisomeric purities are prepared via thermal SO2 extrusion from cis-2,5-disubstituted-2,5-dihydrothiofene-1,1-dioxides generated by a retro Diels-Alder reaction. Applications of this method to the syntheses of two insecticidal natural dienamides : pellitorine and pipercide and of methyl tetradeca-2E,4,5-trienoate, an insect sex pheromone, are described.

Flash-thermolysis of methylenephtalide and 3-methylene-2-coumaranone

Abstract The synthesis and flash-thermolysis of methylenephtalide 1 and 3-methylene- 2-coumaranone 2 are reported. At high temperatures ( ⩾ 1000°C) these two isomeric lactones do not extrude CO 2 but give rise to new clean thermal rearrangements.

Optically active five-membered oxygen-containing rings. A synthesis of (+)-eldanolide

Abstract Stereoselective tandem Wittig-Horner - intramolecular Michael reactions followed by a retro Diels-Alder cleavage convert the optically active tricyclic lactol 1 into 2-substituted 2.5-dihydrofurans of high enantiomeric purities. These compounds are useful synthons for the obtention of natural butenolides and butanolides as illustrated by the synthesis of the pheromone (+)-eldanolide.

Stereoselective aldol condensations induced by a thermolabile group

Abstract Diastereoselective aldol condensations between exo, endo and 2-methyl endo bicyclo[2.2.1]-5-hepten-2-yl ethyl ketones and aldehydes are achieved via the ketones Z-lithium enolates prepared with lithium hexamethyldisilazide. The aldols thus obtained give rise by a retro Diels-Alder reaction to syn α -methyl- β -siloxy- α′ -ethylenic ketones of potential value for polyhydroxylated natural product synthesis.

Stereoselective intramolecular michael addition induced by a thermolabile group: Synthesis of optically active five-membered oxygen-containing rings.

Abstract A tandem Wittig-Michael reaction allows the stereoselective formation of the tricyclic compound 2 from the chiral lactol 1 . A retro Diels-Alder reaction leads to the dihydrofuran 3 of high enantiomeric purity.