Photochemical conversion of cephalosporins, 1-carba(1-dethia)cephalosporins and 1-oxa(1-dethia)cephalosporins

A process for preparing a compound of Formula (I) ##STR7## wherein R is an amino-protecting group, X is --CH.sub.2 --, O, or ##STR8## wherein n is 0, 1, or 2, and R.sub.1 is a carboxy-protecting group;

• and R.sub.2 is hydrogen, C.sub.1 -C.sub.6 alkyl, C.sub.2 -C.sub.6 alkenyl, C.sub.2 -C.sub.6 alkynyl, C.sub.1 -C.sub.6 substituted alkyl, C.sub.2 -C.sub.6 substituted alkenyl, C.sub.2 -C.sub.6 substituted alkynyl, C.sub.1 -C.sub.6 alkoxy, C.sub.1 -C.sub.6 alkylthio, C.sub.2 -C.sub.6 alkenyloxy, C.sub.2 -C.sub.6 alkenylthio, C.sub.2 -C.sub.6 alkynyloxy, C.sub.2 -C.sub.6 alkynylthio, C.sub.1 -C.sub.6 substituted alkoxy, C.sub.1 -C.sub.6 substituted alkylthio, C.sub.2 -C.sub.6 substituted alkenyloxy, C.sub.2 -C.sub.6 substituted alkenylthio, C.sub.2 -C.sub.6 substituted alkynyloxy, and C.sub.2 -C.sub.6 substituted alkynylthio;
• which comprises subjecting a compound of Formula (II) ##STR9## to ultraviolet radiation, wherein X, R, R.sub.1 and R.sub.2 are as defined above.