Effet de solvant lors de la photocyclisation du diphenyl-2,3 benzo(B)furrane

Photochemical transformations of small ring compounds. 92. Intramolecular dipolar cycloaddition reactions with vinylbiphenyl-substituted 1,3-dipoles

“…Rigidly held stilbene moieties are known to yield phenanthrene derivatives on irradiation and provide excellent precedent for this latter transformation. [28][29][30][31] Additional examples of the intramolecular 1,3-dipolar cycloaddition reaction of these vinylbiphenyl-substituted systems were provided by the photolysis of azirines 20 and 23.…”

“…The formation of cycloadduct 28 can be rationalized by the assumption that the initially generated nitrile ylide (i.e., 31) 30, R = H undergoes rapid cycloaddition across the C-N double bond of the adjacent azirine ring to give a transient diazabicyclohexene 32. The high degree of order already present in the transition state undoubtedly enhances the rate of the intramolecular reaction relative to bimolecular cycloaddition with the added dimethyl acetylenedicarboxylate.…”