A comparative Study of the Decomposition of o-Alkynyl-Substituted Aryl Diazo Ketones. Synthesis of Polysubstituted β-Naphthols via Arylketene Intermediates

Article abstract of DOI:10.1021/jo00075a045

The photochemical, thermal, and rhodium-catalyzed decomposition reactions of several closely related o-alkynyl or o-alkenyl α-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 α-diazopropiophenone derivatives yields polysubstituted β-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-alkynylsubstituent.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 ?-system producing a vinyl carbenoid intermediate.Further reaction of the cyclized carbenoid with the starting diazo compound furnished 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.