Olivanic acid analogues. Part 3. Total synthesis of C(6α)-methoxy-substituted 7-oxo-1 -azabicyclo[3.2.0] hept-2-ene-2-carboxylates

Abstract

The reaction of the dianion of 4-allylazetidin-2-one with oxygen gave hydroxylation at the C(3)-position. This intermediate has been converted via the phosphorane (9) into the 6α-methoxyaza-bicycloheptene (13), which was subsequently functionalised with a C(3)-ethylthio substituent. Since the sodium salt corresponding to ester (14) is unstable, the biologically hydrolysable phthalidyl ester (15) was prepared.