ADVANCED INTRAMOLECULAR DIELS-ALDER STUDY TOWARD THE SYNTHESIS OF (-)-MORPHINE - STRUCTURE CORRECTION OF A PREVIOUSLY REPORTED DIELS-ALDER PRODUCT

A tricyclic ring system 18 containing all 5 chiral centers of the natu ral (-)-morphine skeleton has been synthesized in 9 steps. cis-Dienedi ol 11 was produced by a batch microbial dihydroxylation of (2-azidoeth yl)benzene with the E. coli strain JM109(pDTG601). The key step in the synthesis was a thermal [4+2] intramolecular Diels-Alder cycloadditio n of triene 16 which afforded the tricyclic adduct 17 in 62% yield. Af ter deprotection, the absolute stereochemistry of the alcohol 18 was d etermined by X-ray crystallographic analysis. The previously reported Diels-Alder adduct 4a was deprotected and the absolute stereochemistry of the free alcohol was assigned by X-ray crystallography to have the structure 4c. This finding therefore constitutes the correction of th e structure for 4a.