XANTHATE TRANSFER CYCLIZATION OF GLYCINE RADICALS - SYNTHESIS OF 5-MEMBERED AND 6-MEMBERED RING NITROGEN-HETEROCYCLES

Xanthate transfer radical cyclisations of several glycine derivatives and substituted N-methylcarbamates are reported. These reactions proceed via 2-aza-5-alkenyl and 2-aza-6-alkenyl radicals as intermediates which bear an electron-withdrawing carbonyl substituent at nitrogen. The xanthate-mediated cyclisation method renders slow radical cyclisation processes successful, leading to ring systems which are not readily accessible by other methods. The gamma-thio substituent incorporated into the cyclisation product allows the synthesis of two conformationally restricted methionine analogues. An X-ray crystal structure of one of the cyclization products is presented.