TOTAL SYNTHESIS OF (-)-DENTICULATIN-A AND (-)-DENTICULATIN-B - MARINE POLYPROPIONATES FROM SIPHONARIA-DENTICULATA

A synthesis of the marine polypropionates (-)-denticulatin A (2a) and B (2b) is described. The targets, which are β-hydroxy ketones wherein the hydroxyl group is also a tertiary hemiketal, are sensitive to acid dehydration. An open-chain form (26) of the denticulatins, having the 1,3-diol functionality protected as its p-methoxy-acetophenylidene derivative, is prepared and is demonstrated to undergo only one of three possible modes of hemiketalization upon acid hydrolysis. The open-chain structure is constructed by an aldol condensation between ketone 5 and keto aldehyde 25, which is synthesized by the 3-methyl-γ-butyrolactone strategy. © 1990, American Chemical Society. All rights reserved.