A COMPARATIVE-STUDY OF THE DECOMPOSITION OF O-ALKYNYL-SUBSTITUTED ARYL DIAZO KETONES - SYNTHESIS OF POLYSUBSTITUTED BETA-NAPHTHOLS VIA ARYLKETENE INTERMEDIATES

The photochemical, thermal, and rhodium-catalyzed decomposition reactions of several closely related o-alkynyl or o-alkenyl alpha-diazoaceto- and propiophenone derivatives have been studied. The reaction outcome is markedly dependent upon the reaction conditions employed for nitrogen extrusion. Thermolysis or photolysis of o-alkynyl alpha-diazopropiophenone derivatives yields polysubstituted beta-naphthols. These products are derived from Wolff rearrangement of the initially formed carbene to give an aryl ketene which undergoes intramolecular cyclization onto the o-alkynyl substituent. In direct contrast to the thermal and photochemical results, Rh(II)-catalyzed decomposition yields products derived from direct attack of a rhodium carbenoid onto the tethered pi-system producing a vinyl carbenoid intermediate. Further reaction of the cyclized carbenoid with the starting diazo compound furnishes a vinyl indenone which undergoes a rapid intramolecular Diels-Alder reaction to produce a novel dimer whose structure was elucidated by an X-ray crystal analysis. Replacement of the methyl group on the diazo center with a sterically less demanding hydrogen atom was also found to play an important role in controlling the outcome of the Rh(II)-catalyzed reaction.