Dk. Pyun et al., 2,3-Dihydro-4H-1,3-oxazin-4-ones, novel auxiliaries for the stereoselective synthesis of 1 beta-methylcarbapenems, SYNLETT, (12), 2001, pp. 1950-1952
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).