Toward the total synthesis of ansalactam A

Ansalactam A is a recently isolated ansa macrolide containing a spiro-γ-lactam functionality that is structurally distinct from other members of the ansa macrolide family. Herein, we describe synthetic studies toward ansalactam A. A route has been developed for the synthesis of a model system featuring a xanthate, which constitutes a direct precursor for the projected radical cyclization step aimed at the formation of the spiro-γ-lactam moiety of ansalactam A. In this context, a new practical method for the removal of an Evans auxiliary attached to sterically encumbered substrates was developed. The utilization of β-lactones as an acylation reagent, an alternative to commonly used amide coupling reactions, is described.