Allenyl ester precursors for 1H-inden-1-ol carboxylates: comparisons with their propargylic equivalents having terminal alkyne functions

The reactivity of allenyl carboxylates, Ar(R1)CCCH(O2CR2) and their isomeric equivalents the terminal propargylic carboxylates, ArC(R1)(O2CR2)CCH, in gold-catalyzed carbocyclization to indenes provides information on 1,3 and 1,2-carboxylate shifts associated with their interconversion. Allenyl carboxylates transform specifically to 1H-inden-1-yl carboxylates in high yields, under AuI-catalysis. Their equivalent propargylic carboxylates give complex mixtures of indene isomers and elimination products. Mechanistic tests indicate that interconversion of the terminal propargylic carbonate to its allene is at best slow in this case.