The regioselectivity of cycloaddition reactions between diazomethane and 3-vinylcephalosporins
Abstract
Diphenylmethyl (6R,7R)-7-phenylacetamido-3-vinylceph-3-em-4-carboxylate 1 undergoes regioselective addition of diazomethane to give the 1-pyrazoline 7, which readily undergoes thermolysis to give the cyclopropyl analogue 10. The regioselectivity is reversed, however, when one or more electron withdrawing ester substituents are attached to the 3-vinyl group.