Scalable DOS-like Strategy to the δ-Amino Acids via Petasis/Cross Metathesis Reactions Sequence.

A convenient and scalable approach to δ,δ-spirosubstituted δ-amino acids and their α,β-unsaturated analogues from bulk ketones was elaborated. The proposed routes include Petasis reaction of starting ketone with allylboronic acid pinacol ester and methanolic ammonia, and cross metathesis with acrylic acid derivatives as key steps. The developed protocols are novel, robust, and economically efficient. They avoid tedious separation and purification, can be scaled up to 40 g of final compounds and propose an efficient way to novel conformationally rigid foldamers.