Efficient, Stereoselective Synthesis of Oxazolo[3,2-a]pyrazin-5-ones:  Novel Bicyclic Lactam Scaffolds from the Bicyclocondensation of 3-Aza-1,5-ketoacids and Amino Alcohols

The bicyclocondensation of 3-aza-1,5-ketoacids and amino alcohols furnished novel oxazolo[3,2-a]pyrazin-5-one scaffolds possessing angular, ring junction substituents in high yield with excellent levels of substrate-based diastereocontrol. Mild oxidation of serinol-derived scaffolds provided access to a new class of constrained dipeptide surrogates. Deprotection of the endocyclic amine contained within these scaffolds allows for further diversification via N-functionalization.