AN ALTERNATIVE DIASTEREOSPECIFIC APPROACH TO (+ -)-SAMIN AND 2,6-DIARYL-3,7-DIOXABICYCLO[3.3.0]OCTANE [FURANOFURAN] LIGNANS BASED ON THE IRELAND-CLAISEN REARRANGEMENT OF UNSATURATED OXA-MACROLIDES/

Ireland-Claisen rearrangement of the nine-membered macrolide 22 leads stereospecifically to the tetrahydrofurancarboxylate 23, via the boat- like transition state 9, The hydroxy-acid precursor 21c to the macroli de 22 has been prepared by Michael addition of the sodium alkoxide of( Z)-allylic alcohol 20 to methyl acrylate in the presence of dimethyl s ulfoxide, Subsequent conversion into the corresponding aldehyde 29, Gr ignard addition, cleavage of the alkene and acid-catalysed cyclisation gives (+/-)-sesamin 32. The epimeric ester 33 has been converted into (+/-)-samin 37 by related functional group manipulations, but excludi ng the Grignard coupling, and a final isomerisation.