REARRANGEMENT OF ALKYNYL AND VINYL CARBENOIDS VIA THE RHODIUM(II)-CATALYZED CYCLIZATION REACTION OF ALPHA-DIAZOKETONES

o-Alkynyl-substituted alpha-diazoacetophenones undergo facile cyclization to indenone derivatives upon treatment with catalytic quantities of Rh(II) carboxylates. The cyclization reaction involves addition of a rhodium stabilized alpha-keto carbenoid onto the neighboring acetylenic pi-bond to give a cyclized vinyl carbenoid. When an alkene is tethered to the alkynyl group, the vinyl carbenoid complex undergoes further cyclization to produce a cyclopropenyl-substituted indenone. Different enyl substituents resulted in a significant variation in the behavioral pattern of the reactive cyclopropene ring. The strained cyclopropene ring was intercepted with diphenylisobenzofuran to give Diels-Alder cycloadducts. For alkynyl substituted alpha-diazo ketones, the resulting vinyl alkynyl carbenoids were found to give products derived from an unusual alkynyl carbenoid rearrangement. The Rh(II)-catalyzed reaction of several o-dialkynyl-substituted alpha-diazoacetophenones which contain a group capable of undergoing reaction with the carbenoid at the terminal position was examined. Products derived from a 1,2-hydrogen shift as well as cyclopropanation of a tethered alkene was obtained in high yield. In addition, the thermal decomposition of a series of aziridinylimines derived from alkynyl-substituted aldehydes led to products derived from a rearranged alkynyl carbene. The initially formed alkynyl carbene at C1 could be induced to undergo exclusive reaction at the C3 terminal position.