Synthetic organic chemistry based on small ring compounds.

Small ring systems are important topics in both organic and inorganic chemistry, and draw considerable attention from both theoretical and preparative perspectives. This review intends to summarize the studies, focusing on the preparative aspects, that have been carried out in our laboratory. Namely, synthesis of (+)- and (-)-alpha-cuparenone, (+)-ipomeamarone, (+)-epiipomeamarone, (-)-ngaione, (-)-alpha-bisabolol, (-)-aplysin, (-)-debromoaplysin, (-)-mesembrine, (-)-filiformin, (-)-debromofiliformin, and (-)-4-deoxyverrucarol via successive asymmetric epoxidation and enantiospecific ring expansion of cyclopropylidenes, (+)-equilenin via successive ring expansion-insertion reaction, estrone, estradiol, chenodeoxycholic acid, 19-norspironolactone, 19-nordeoxycorticosterone, cortisone, adrenosterone, 11-oxoprogesterone, and 1alpha,25-dihydroxyvitamin D3 via intramolecular cycloaddition reaction of o-quinodimethanes. Medicinal chemistry aiming at developing a new type of anti-influenza agent, novel reaction mode of electrocyclic reaction, and substituent effect on that reaction are also discussed.