Abstract
The tricyclic nucleus 9b of ceroplastol I and ceroplasteric acid has been synthesized stereoselectively and enantioepedfically in only 10 steps from 1-cyclopentenecarboxaldehyde. Addition of (3-methyl-3-butenyl)magnesium bromide to imine 13b and methylation with methyl iodide by Koga’s procedure gave 94% of optically pure aldehyde 40 as previously described in our reiswigin A synthesis. Isomerization of the double bond of aldehyde 40 with HI afforded aldehyde 17b. Coupling of the enolate prepared from silyl enol ether 45 with aldehyde 17b gave a 1:1 mixture of 46a and 46b, which contain the complete carbon skeleton of 9b, in only three steps. Dehydration provided enones 47a and 47b. Reduction of 47a and 47b with Li/NH3 afforded saturated ketones 48at and 48bt that were reduced with LiAlH, to the saturated alcohols 49att and 49btt. Protection of the alcohols as the TBDMS ethersandoxidativecleavageofthedienesaffordedreadilyseparableketoaldehydes51and56. McMurrycoupling of 51, cleavage of the silyl ether, and oxidation of the alcohol with PCC completed the synthesis of 9b.