
TY  - JOUR
A1  - Davis, M 
A1  - Wu, WY 
T1  - A New Dihydrothiazine Ring Closure for the Preparation of 3-Methylcephalosporins From Azetidinone Disulfides at 5-10-Degrees
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1987
VL  - 40
IS  - 9
SP  - 1519
EP  - 1526
KW  - 
UR  - https://doi.org/10.1071/CH9871519 
N2  - p - Nitrobenzyl (2R,3R)-2-(benzothiazol-2'-yldithio)-&#945;-isopropenyl-4-oxo-3-phenoxyacetylaminoazetidine-1-acetate (3a), readily prepared from penicillin V, is smoothly cyclized by ammonium acetate in a dimethyl sulfoxideltetrahydrofuran mixture at 5-10º to the ceph-3-em ester (2a) in high yield. Other esters (3b-d), but not the free acid (3e), behave in a similar way. The ceph-3-em esters can be readily de-esterified to the free acid (2e). 
ER  -

