Stereocontrolled synthesis of tricyclic fused oxazolidinone as antibacterial agent

Tricyclic fused oxazolidinone 3a and 3b have been synthesized as antibacterial agents in 12 and 11 steps respectively. The key intermediates 10a and 10b have been developed via opening of epoxide 9a and 9b and cyclization by the resulting oxygen anion attack.