Synthetic Studies Aimed at the Dolastanes. An Attempted A + C -> ABC Approach

Article abstract of DOI:10.1021/jo00221a027

The dolastanes are marine diterpenes whose molecular array of fused 6-7-5 alicyclic rings is distinctive.As part of a program directed toward the synthesis of representatives of these bioactive natural products, the possibility of elaborating their framework by intramolecular cyclization to form the central seven-membered ring has been examined.An expedient two-step route to keto ester 8 was developed.This intermediate proved receptive to copper-promoted conjugate addition of allylmagnesium bromide and <(E)-2-(trimethylsilyl)vinyl>lithium.The acetal 21 to be subsequently derived from these adducts could be conveniently crafted into the highly functionalized 2-cyclopentenones 27.Central to the synthetic strategy was the need for intramolecular C-C bond formation within 27.Because we were singularly unsuccessful in achieving the desired end result, this particular approach appears unsuited for gaining access to the dolastanes.