Novel Stereocontrolled Approach to syn-and anti-Oxepene-Cyclogeranyl trans-Fused Polycyclic Systems:Asymmetric Total Synthesis of (-)-Aplysistatin,(+)-Palisadin A,(+)-Palisadin B,(+)-12-Hydroxy-Palisadin B,and the AB Ring System of Adociasulfate-2 an

摘要

A new Stereocontrolled method for the formation of trans-anti cyclogeranyl-oxepene systems is described.The demanding stereochemistry is secured by stereoselective coupling of a cyclogeranyl tertiary alcohol with a 1,2-unsymmetrically substituted epoxide,while the formation of the highly strained oxepene is achieved employing ring-closing metathesis.Since the stereochemistry of the trans-fused 6,7-ring system is determined by the epoxide,the method also allows the construction of trans-syn 6,7-ring systems.This approach leads to the synthesis of the AB fragment of Adociasulfate-2 and Toxicol A,for the first time.The flexibility and efficiency of the presented strategy is demonstrated by the total asymmetric synthesis of (-)-Aplysistatin,(+)-Palisadin A,(+)-12-hydroxy-Palisadin B,and (+)-Palisa-din B,employing two similar key intermediates.