Reaction of cerium(IV) ammonium nitrate with 3-methylcephalosporins: synthesis of a 2-methoxy-3-methylcephalosporin
The cephalosporins (1)–(3) react with cerium(IV) ammonium nitrate (CAN) in aqueous acetic acid to give the thiazoles (4)–(6) respectively as the major products. The minor products from the reaction of the cephalosporin (1) with CAN in aqueous acetic acid were the esters (7), (8), (10), and (11). The cephalosporin (1) reacted with CAN in methanol under mild conditions to give a good yield of the 2-methoxy derivative (13). More vigorous conditions for the reaction of (1) and CAN in methanol gave a lower yield of the cephalosporin (13) and gave the esters (4). (11), (14), (15) and methyl phenylacetate as additional products. The mechanism involved in this oxidative rearrangement of the cephalosporins (1)–(3) is discussed.