Palladium(0)‐catalysed conversion of α‐acetylenic epoxides into α‐allenic alcohols. Novel route to (±)‐2,3‐octadiene‐5,7‐diyn‐1‐ol, a metabolite from fungus <i>Cortinellus berkeleyanus</i>

Abstract

Abstract α‐Acetylenic epoxides,R′CCCR″CH 2 (1), have been converted into α‐allenic alcohols, RR′CCCR″‐CH 2 OH (3), by means of a palladium(0)‐promoted reaction with R‐ZnCl (2; R: Me 3 Si(C≡C) n ‐(n=1 or 2), H 2 CCH‐ or t‐BuCHCCH‐). Using this method, an improved synthesis of (±)‐2,3‐octadiene‐5,7‐diyn‐1‐ol, a metabolite from fungus Cortinellus berkeleyanus, has been developed. The method is not suited to the preparation of α‐allenic alcohols from 1 and, for example, BuZnCl because of substantial formation of reduction products, HCR′CCR″‐CH 2 OH. For the preparation of 3 from R = Me 3 SiC≡C other acetylides Me 3 SiC C‐M were also studied, viz. M = Li, MgCl, Cu or Cu 1/2 Li 1/2 but only with the cuprate could a reasonable conversion of 1 be realized.