TOTAL SYNTHESIS OF (+/-)-GNIDIDIONE AND (+/-)-ISOGNIDIDIONE

(±)-Gnididione (1) and (±)-isognididione (2) have been prepared in a totally stereospecific fashion beginning with the oxazole aldehyde 20, which was efficiently elaborated to the tertiary alcohols 3Z-R and 3E-R by a chelation controlled addition of 1-propynylmagnesium bromide to the intermediate enones 24Z and 24E. Alcohol 3Z-R was converted in a single step to 1 via a process involving sequential chemoselective oxy-Cope reaction to produce the acetylenic ketone 5, intramolecular Diels—Alder reaction of 5 to afford gnididione ketal 7, and acid hydrolysis. In identical fashion, 3E-R was directly converted to 2 with 100% stereoselectivity. © 1990, American Chemical Society. All rights reserved.