Asymmetric Synthesis of α-Substituted β-Formyl δ-Lactones via a Michael Addition/α-Alkylation Protocol

Asymmetric synthesis of succinic semialdehyde derivatives

The nucleophilic Michael addition of 2-(diphenylmethoxymethyl)-1-methyleneamino pyrrolidine 1Dto prochiral aliphatic and aromatic alkylidene malonates 2 takes place in the presence of MgI(2) to afford the corresponding Michael adducts 3 in excellent yields and good selectivities. In the aromatic series, optically pure (de > 98%) major diastereomers (S,S)-3 were isolated in good yields (77-93%) after chromatographic separation. Direct, racemization-free BF(3).OEt(2)-catalyzed thiolysis of compounds 3 afforded dithioacetals 7. These compounds were transformed into malonates 8 and succinic semialdehyde derivatives 9 by Raney Nickel mediated desulfuration or decarboxylation, respectively.

Asymmetric Michael addition of formaldehyde N,N-dialkylhydrazones to alkylidene malonates

Enantiopure formaldehyde N,N-dialkylhydrazones 1 smoothly react with prochiral alkylidene malonates 2 in the presence of MgI2 to afford the corresponding Michael adducts 3 in excellent yields and good diastereoselectivities; direct racemization-free BF3.OEt2-catalyzed thiolysis of the hydrazone C=N bond affords the corresponding dithioketals 7 in optically pure or enantiomerically enriched form.