Weighing different mechanistic proposals for the Dotz reaction: A density functional study

Three different routes have been theoretically explored for the benzannulat ion of heteroatom-stabilized chromium carbene complexes with ethyne (Dotz r eaction). The most widely accepted mechanistic proposals assume that the ce ntral part of the reaction proceeds through either the vinylketene route (D otz's hypothesis) or the chromacycloheptadienone route (Casey's suggestion) . Our calculations reveal that, from a thermodynamic viewpoint, the latter proposal is surpassed by the former, because conversion of vinylcarbenes in to chromacycloheptadienones is computed to be a notably endothermic process . Moreover, a recently postulated new third route is found to be an even be tter proposal than the one from Dotz's hypothesis since it involves lower e nergy barriers and more stable intermediates than the vinylketene route pos tulated by Dotz. The novel findings query revision of the classically assum ed paths and are a doorway to new formulisms for the mechanism of the title reaction.