TiCl4-promoted aldol condensations of S-4-chlorophenyl thioesters with enals or dienals led to the production of dienyl or trienyl thioesters in good yields. Due to good crystallinity, products with high E/Z ratios were obtained by simple filtration in many cases. Reduction of the thioester moiety by DIBAL-H afforded the corresponding unsaturated aldehydes while suppressing the E/Z-isomerization and
Ti-direct, powerful, stereoselective aldol-type additions of esters and thioesters to carbonyl compounds: application to the synthesis and evaluation of lactone analogs of jasmone perfumes
thiophenyl esters or thioaryl esters with aldehydes and ketones was performed (total 46 examples). The present method is advantageous from atom-economical and cost-effective viewpoints; good to excellent yields, moderate to good syn-selectivity, substrate variations, reagent availability, and simple procedures. Utilizing the present reaction as the key step, an efficient short synthesis of three lactone
(2S,3S,4R)-4-Amino-3-hydroxy-2-methylpentanoic acid, a novel aminoacidconstituent of bleomycin, has been synthesized stereoselectively through aldol condensation of (R)-2-aminopropionaldehyde derivatives and E-vinyloxyboranes.
An efficient TiCl4/amine-promoted aldol-type addition of phenyl and phenylthio esters with aldehydes or ketones has been performed. The present method includes a practical merit from the green chemical viewpoint with regard to yields, variations of substrates, availability of reagents, and simple operations.