Stereoselective aldol reaction of α-seleno carbonyl compounds: preparation of ( Z)-α,β-unsaturated carbonyl compounds

Abstract

The aldol reaction of the titanium enolates of α-seleno esters in the presence of Ph 3P or Ph 3PO gave the products with high stereoselectivity favoring the syn isomers. Reaction of α-seleno ketones with TiCl 4 in the presence of 2 equiv. of Et 3N, and subsequently with aldehydes, gave the aldol products with high syn selectivity. The stereoselectivity in the aldol reaction of 3-pentanone also increased by using an excess amount of Et 3N. The aldol products thus obtained from the α-seleno carbonyl compounds could be stereospecifically converted to ( Z)-α,β-unsaturated carbonyl compounds by treatment with pyridine. ( Z)-Alkylidenecyclopentanones were exclusively formed by treatment of the syn-aldol products with Et 3N in the dark.