Studies toward the total synthesis of di- and sesterterpenes with a dicyclopenta[a,d]cyclooctane skeleton. Construction of a versatile A/B ring building block via a ring-closing metathesis reaction and carbocationic rearrangement

• DOI: 10.1016/j.tetlet.2004.12.077
• Publication Date: 2005-01-11T12:29:43Z
• Authors: Karol Michalak; Michał Michalak; Jerzy Wicha
• Keywords: 01 natural sciences; 0104 chemical sciences

Abstract The cyclopentacyclooctane derivative 1 , chosen as the key building block in a synthesis of terpenoid ophiobolates and fusicoccins, has been prepared from 2-methylcyclo-pent-2-en-1-one 5 . Cyclization of the intermediate 1,9-diene of l , u configuration 10 under metathesis conditions (Grubbs’ catalyst 15 ) afforded the eight-membered ring product 13 , whereas cyclization of the l , l diastereomer 9 produced a seven-membered ring analog 12 . Cationic rearrangement of epoxide 26 occurred with methyl group migration to give ketone 27 as the major product.