Synthesis of functionalised cephalosporins : Diphenylmethyl(1S,6R,7S)-3-bromomethyl-7-formamido-7-methoxyceph-3-em-4-carboxylate-1-oxide: a useful intermediate in the preparation of 7α-methoxycephalosporins

The N-formamido cephalosporins 4a and4b undergo direct methoxylation at the Pα-position to give the 7α-methoxy derivatives 5a and 5b. These were converted to other 7β-acylamido compounds by the sequence : oxidation, deformylation, acylation and reduction. The 3-bromomethyl derivatives 2b,6b and 8b proved amenable to nucleophilic substitution with 5-mercapto-1-methyltetrazole.