CEMBRANOLIDE TOTAL SYNTHESIS. ANISOMELIC ACID

Article abstract of DOI:10.1016/S0040-4020(01)87668-7

The stereoselective total synthesis of (+/-)-anisomelic acid (34) has been achieved starting from aldehyde 7, the ozonolysis product of geranyl acetate.Two key steps ensured the stereoselectivity of the synthesis.The first entailed a highly anti-selective addition of the allyltitanium derived from carbamate 15 to aldehyde 5 affording the enol carbamate allylic alcohol 16.The second was a highly (Z)-selective Horner-Emmons cyclization of the derived phosphono ester aldehyde 25 leading to the conjugated ester 27.Further conversion led to the crystalline lactone 30 whose structure was confirmed through single crystal X-ray analysis.Equilibration of the conjugated double bond of 30 gave rise to a 1:1 mixture of the (Z) and (E) isomers.This result was foretold by molecular mechanics calculations.