SIMPLE AND CONDENSED BETA-LACTAMS .18. ON THE ANOMALOUS BEHAVIOR OF (3RS,4RS)-[(2RS)-3-ACETYLTHIAZOLIDIN-2-YL]-1-(4-METHOXYPHENYL)AZETIDIN-2-ONES TOWARDS CERIUM(IV) AMMONIUM-NITRATE (CAN) - AN UNPRECEDENTED OXIDATIVE RING TRANSFORMATION

Starting with (2RS:3RS)-1-(4-methoxyphenyl)-4-oxo-3-phthalimidoazetidine-2-carbaldehyde (1) the two diastereoisomeric 4-(3-acetylthiazolidin-2-yl)-1-(4-methoxyphenyl)-3-phthalimidoazetidin-2-ones 4a and 5a were prepared and converted into their 3-allyloxycarbonylamino analogues 4c and 5c, respectively. While the (3RS,4RS,2SR) isomers 4a and 4c were readily N-deprotected with cerium (IV) ammonium nitrate (CAN) to yield the expected 6a and 6c, respectively, treatment of the (3RS,4RS,2'RS) isomers 5a and 5c with CAN led to compounds 7a and 7c, respectively, via oxidative ring transformation. The structure of compound 7a was established by an X-ray diffraction study. A rationale, based on AM1 and calculations is given for the dissimilar behaviour of the diastereoisomers.