Petasis-type reactions for the synthesis of substituted pyrrolidin-2-ones

Pyrrolidin-2-ones are important heterocyclic motifs found in natural products and biologically active synthetic molecules. Addition of nucleophiles, incl uding allylsilanes, isonitriles and organometallics , to N - acyliminium ions represents one of the most commonl y used approaches for the formation of substituted pyrrolidin-2-ones. Only few studies on the nucleoph ic addition of organoboronic acids to N -acyliminium ions have been reported. Herein, we disclose our re cent efforts for the synthesis of substituted pyrro lidin- 2-ones through Lewis-acid-mediated Petasis-type rea ctions. By implementing a reductive cyclization reaction, linear L -malic acid derivatives were rapidly converted into cyclic N -acyliminium ions. Under the optimized conditions, entailing the use of HFIP as solvent, both electron-rich and electron-deficient boronic acids were successfully added to a range of cyclic N -acyliminium ions, typically with excellent diastereoselectivity with electron-deficient boroni c acids.