Mitsunobu C-Alkylation of Meldrum's Acids

C-Dialkylation of Meldrum's acid (2a) and 5-benzyl Meldrum's acid (2b) can be achieved through Mitsunobu dehydration using allylic and arylmethyl alcohols as alkylating agents. This is the first time that the Mitsunobu reaction is successfully applied to the C-alkylation of a highly enolizable cyclic β-dicarbonyl system. With primary (allylic and arylmethyl) alcohols, the alkylations always take place at the carbon bearing the hydroxy group. For secondary allylic alcohols, a catalytic amount of Pd(0) must be added to enhance the regioselectivity of C-alkylation over O-alkylation. With (Ph₃P)₄Pd(0) as a catalyst, the reaction occurs specifically at the less hindered carbon, and the configuration of the resultant double bond is always trans. Attempts to monoalkylate Meldrum's acids 2a and 2b failed.