UNSYMMETRICAL CONNECTIVE OLEFINATION BY KORNBLUM NITRO-SYNTHESIS : APPLICATIONS IN PHYTUBERIN CHEMISTRY

Article abstract of DOI:10.1016/S0040-4020(01)87381-6

Kornblum unsymmetrical olefin synthesis employing radical-anion chain crossed-coupling (light catalysed) of a mono- and a gem-di-nitro-compound, followed by reductive NO2 removal, is examined in the context of a hindered olefin structure required for phytuberin synthesis.Whilst successful for a tetrasubstituted olefin model (for which a Witting approach failed), increasing substitution on the β-position of the mono-nitro component supressed the coupling reaction, presumably for steric reasons.An alternative coupling involving a bromonitrocyclohexane and a mononitroacetal caused symmetrical coupling of the mononitro-component in high yield, rather than a crossed reaction.Reductive elimination (using Na2S/DMF) from either rac.- or meso- 1,2-dinitro-1,2-diphenylethane leads to (E)-stilbene < >98percent (E) > probably through a stabilised radical or anion.A convenient preparation of triphenylisoxazoline-N-oxide is reported.