New α-phosphono-β-aryl- or β-heteroaryl-substituted α,β-unsaturated dithioesters 2 were easily prepared from diethyl phosphonodithioacetate 1 and used as thiadienes in thermal or highpressure hetero Diels–Alder cycloadditions with enol and thioenol ethers. The resulting new phosphono 3,4-dihydro 2H-thiopyrans 3 were isolated in excellent yields and with a cis- or trans-diastereoselectivity depending
Phosphonoketene dithioacetals 3a-e were obtained in good yields by the reaction of ethyl phosphonoacetates 1a,b with 2-4 equiv of thiols 2a-c in the presence of an alkylaluminum dichloride or dialkylaluminum chlorides. Reaction of 2,2-dithio-1-phosphonovinyl anions with aldehydes afforded allylic alcohols 4-7, 11-18 in good to moderate yields. Treatment of the alcohols 4-6 with t-BuOK in THF led to
The formation of a transient Michael adduct, triggering an
in-situ isomerization of the heterodiene, is postulated to explain
the reversal of the diastereoselectivity of high pressure-promoted
hetero-DielsâAlder reactions carried out in the presence of
pyridine.