2,3-Dihydro-4H-1,3-oxazin-4-ones, novel auxiliaries for the stereoselective synthesis of 1 beta-methylcarbapenems

Dihydrooxazinones 9 prepared from benzylcyanide in two steps serve as effic ient auxiliaries for the stereoselective synthesis of beta -methylcarbapene m intermediate 2. Reformatsky-type reactions of 4-acetoxyazetidinone with a -broinopropionyl dihydrooxazinone 10 provided beta -methylazetidinones 4 in high diastereoselectivities. The auxiliaries 9 were also easily removed in the Dieckmann cyclization leading to beta -methylcarbapenem skeletons. Pra ctical synthesis of beta -methylenolphosphates 2 from 4-acetoxyazetidinone 3 was achieved in three steps (61-77% overall yield).