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Abstract
α,β-Unsaturated thiocarbonyl compounds substituted by a secondary amino group in position β, such as thioamide vinylogs, dithiocarbamate vinylogs or thioaroylformamidines react with lithium enolates of esters, ketones or amides to give 1,4-addition compounds.
In the presence of magnesium bromide 1,4-adducts undergo an intramolecular cyclization to give 2H-thiopyranones. Methylation of the 1,4-adducts is followed by a stereospecific elimination of the amine and leads to (1-Z)-1,3-dienic carbonyl compounds: with thioamide vinylogs, δ-methylthio-α,β,γ,δ-diethylenic ketones, esters and amides are obtained. Dithiocarbamate vinylogs give the α-ethylenic ketene dithioacetals, with a carbonyl function in δ-position.
Substituted dihydrothiophenes and thiazolines are prepared by the reaction of ethyl α-chloro-α-lithiopropionate with aminopropenethione and thioaroylformamidine respectively.