CARBONYLATIVE RADICAL CYCLIZATION APPROACHES TO TRI-QUINANE AND TETRA-QUINANE - SEQUENTIAL FORMATION OF 3, 4 AND 5 CARBON-CARBON BONDS

Tandem radical cyclizations and carbonylative tandem cyclizations of 5 ,5-disubstituted cyclopentadienes provide a variety of interesting pro ducts. Standard tandem cyclization of 9 provides an epimeric mixture o f angular triquinanes, but carbonylative cyclization of the related pr ecursors 7, 18 and 22 provides new products resulting from a 'round tr ip' radical rearrangement that occurs by a carbonylation, three succes sive cyclizations and a fragmentation. Double carbonylation of 25 occu rs with triple cyclization and no fragmentation to produce tetracycle 26 as the principal product.