Synthesis of Disubstituted Pyrazino‐Oxazine Derivatives with Controlled Stereochemistry

Abstract

Herein, we report a simple synthesis of disubstituted pyrazino‐oxazines with controlled stereochemistry using readily available building blocks: N‐Fmoc‐protected α‐amino acids and 2‐bromo ketones. The convenient solid‐phase synthesis afforded polymer‐supported derivatives of N‐alkylated N‐acylated tert‐butylserine, which were subjected to spontaneous cyclative cleavage to yield the corresponding pyrazine intermediates. The target 1,7,8,9a‐tetrahydropyrazino[2,1‐c][1,4]oxazine‐6,9‐diones were obtained in two steps by acid‐mediated cleavage of the tert‐butyl group followed by cyclization of the oxazine scaffold.