Flash vacuum pyrolysis of 5-(indol-2- and -3-ylmethylene)-2,2-dimethyl-1,3-dioxane-4,6-diones

Abstract

Flash vacuum pyrolysis of 5-(indol-2- and -3-ylmethylene)-2,2-dimethyl-1,3-dioxane-4,6-diones results in the initial formation of indolylmethyleneketenes, which generally either lose carbon monoxide to produce ethynylindoles or undergo [1,5]-sigmatropic shifts, followed by electrocyclic rearrangements, to yield carbazolols or benz[c,d]indol-5(1H)-one. 5-(Indol-2-ylmethylene)-2,2-dimethyl-1,3-dioxane-4,6-dione and the 3-methylindol-2-yl derivative both yield 3H-pyrrolo[1,2-a]indol-3-ones via a [1,7]-sigmatropic rearrangement of the initially formed ketene.