Dithio and thiono esters, LX: Addition of dithioic acid dianions to aldehydes and ketones

Article abstract of DOI:10.1002/ardp.19933261212

Aliphatic dithiocarboxylic acids such as dithioethanoic acid (1a), dithiopropanoic acid (10a) or 2-methyl-dithiopropanoic acid (10e) react with 2 moles of n-BuLi to form the corresponding dilithium dithioenolates 2a, 11a or 11e. These add to aldehydes and ketones to give the aldol adducts 3a-f and 12a-e. Methylation with methyl iodide leads to the more stable β-hydroxy dithioesters 4 and 13. The esters 4 have been dehydrated to yield the α,β-unsaturated dithioesters 5. Addition of the dilithium dithioenolate 2a to methylvinyl ketone, cyclohexenone or cyclopentenone followed by methylation gives rise to the δ,ε-unsaturated dithioesters 6-8.