Mitsuru Tanemura

Cyclization of polyenes: VI. Biogenetic-type synthesis of levantenolides isolated from Turkish tobacco☆

Abstract Keto acid (VII) was assumed to be a precursor in the biogenesis of levantenolides (IV and V). The syntheses of the analogous compounds (IX and X) and their cyclization to IV and V were carried out as follows. Reaction of farnesyl bromide (XV and XX) with 2,2′-di-3-methylfurylmercury afforded the corresponding furano derivatives (XVI and XXI), which were photo-oxidized to butenolide derivatives (IX and X). Biogenetic-type cyclization of IX and X with stannic chloride afforded IV, V, and XIX in moderate yields.

Biogenetic-type synthesis of α- and β-levantenolides

C20-Butenolide (IV), which was derived from the reaction of monocyclofarnesyl bromide (VIII) and 2,2′-di-3-methylfurlylmercury followed by photo-oxidation, afforded α- and β-levantenolides [(I) and (II)] by treatment with anhydrous stannic chloride.