Stereoselective aldol additions of titanium enolates of N-acetyl-4-isopropyl-thiazolidinethione

The addition of chlorotitanium enolates of N-acetyl isopropyl thiazolidine-2-thione to aldehydes was investigated. The stereoselectivity of the aldol products was controlled by the number of equivalents of base added. The syn aldol product was obtained preferentially when 2 equiv of Lewis acid and 1 equiv of base were employed. The anti aldol product was obtained preferentially when 1 equiv of Lewis acid and 2 equiv of base were employed for unsaturated aldehydes. Unexpected results were found with hindered aldehydes when 2 equiv of base were employed.