Studies on the Terpenoids and Related Alicyclic Compounds. Part XLI. Stereoselective Synthesis of Both Half Segments for (-)-Sarcophytonin A and (-)-Sarcophytoxide.
Studies on the Terpenoids and Related Alicyclic Compounds. Part XLI. Stereoselective Synthesis of Both Half Segments for (-)-Sarcophytonin A and (-)-Sarcophytoxide.
Studies on the Terpenoids and Related Alicyclic Compounds. Part XLI. Stereoselective Synthesis of Both Half Segments for (-)-Sarcophytonin A and (-)-Sarcophytoxide.
A stereoselective synthesis of a dihydrofuran derivative (5) and an allylhalide (8), possible precursors of the cembranes (-)-sarcophytonin A and (-)-sarcophytoxide, is described. The optically active dihydrofuran, right half, segment (49) was synthesized starting from a naturally occurring monoterpene, (-)-carvone. It was converted into the phenylselenide (14) via three steps. Oxidation of 14 with m-chloroperbenzoic acid and then treatment with pyridine yielded the epoxy olefin (29). Cleavage of the epoxide with boron trifluoride etherate gave the methoxy alcohol (31). Bromoetherification with N-bromosuccinimide selectively yielded the cis-hexahydro-1-oxaindan derivative (36) having a new chirality at the C-6 position. Reductive debromination of 36 followed by oxidation and then enol silylation yielded the less substituted silyl enol ether (39). Ozonolysis of 39 followed by methylation and elimination of methanol with potassium tert-butoxide and then reduction with 9-borabicyclo[3.3.1]nonane (9-BBN) gave the dihydrofuran derivative (41). Protection as the silyl ether (42) and phenylselenenylation and then treatment with hydrogen peroxide yielded the unsaturated ester (45). Reduction followed by thiophenylation of the resulting hydroxyl group afforded the dihydrofuran derivative (49) as a right half segment. Left half segments, the chloride (53) and the bromide (54), were synthesized starting from geraniol via several steps.