Synthesis of eight- and nine-membered carbocycles through a ring-closing metathesis/ring fragmentation strategy: a rapid and versatile approach to bicyclo[6.4.0]- and bicyclo[7.4.0]alkene ring systems.

Ring-closing metathesis (RCM) of cis-2,6-dialkenyl-2-hydroxy-1-cyclohexanones affords bicyclo[3.n.1]alkenones that are easily converted into eight- or nine-membered carbocycles by oxidative cleavage of the keto-bridging tether. Since the starting cyclohexanones are readily assembled from commercially available 1,2-cyclohexanedione, the overall process constitutes a rapid and versatile route to medium-sized carbocycles, which are otherwise difficult compounds to assemble using currently available procedures. If one of the alkenes of the cyclohexanone chains is replaced by an alkyne, the subsequent RCM produces 1,3-diene systems capable of undergoing stereoselective Diels-Alder reaction with activated dienophiles. Oxidative cleavage of the keto bridge of the resulting tricycles leads to 8-6 and 9-6 fused bicarbocycles with up to four stereocenters.