A versatile approach to (4S,5R)-4-benzyloxy-5-(α-hydroxyalkyl)-2-pyrrolidinones: Experimental evidences to the computational predictions

摘要

A versatile and highly diastereoselective fourr-step approach to (4S,5R)-N-benzyl-4-benzyloxy-5-(α-hydroxyalkyl)-2-pyrrolidi-nones 2, which starts from readily available (S)-N,O-dibenzylmalimide (5), is reported. Substituted 2-pyrrolidinones 2 are valuable building blocks for the asymmetric synthesis of hydroxylated pyrrolidine alkaloids. The method demonstrates high diastereoselec-tivities at the pyrrolidinone ring (C-4/C-5 trans), and low diastereoselectivities at the carbinolic center. Some interesting phenomena such as a remarkable difference in reactivity between the two diastereomeric N,O-acetals 6 towards the dehydration reactions, the isomerization of trans-diastereomers to cis-diastereomers (6), and the exclusive formation of (E)-enamides 8 were observed. These results provide experimental proofs to our previous computational predictions, or have been rationalized by calculations.