Weighing Different Mechanistic Proposals for the Dötz Reaction:  A Density Functional Study

Abstract

Three different routes have been theoretically explored for the benzannulation of heteroatom-stabilized chromium carbene complexes with ethyne (Dötz reaction). The most widely accepted mechanistic proposals assume that the central part of the reaction proceeds through either the vinylketene route (Dötz'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 into chromacycloheptadienones is computed to be a notably endothermic process. Moreover, a recently postulated new third route is found to be an even better proposal than the one from Dötz's hypothesis since it involves lower energy barriers and more stable intermediates than the vinylketene route postulated by Dötz. The novel findings query revision of the classically assumed paths and are a doorway to new formulisms for the mechanism of the title reaction.

Dötz Benzannulation Reactions: Heteroatom and Substituent Effects in Chromium Fischer Carbene Complexes

“…The use of computational tools in such cases is highly recommended to help in elucidating the reaction mechanisms. [34,35] Indeed, some mechanistic details of this paradigmatic reaction have already been investigated from a theoretical point of view by our group [36][37][38] and by others. [39,40] Scheme 2 shows the most viable reaction mechanism proposals explored in these previous works.…”

“…The particular orientation of the carbene ligand in 8 favors the migration of CO because, during the transformation, each of the two p* orbitals of www.chemeurj.org CO can interact concertedly with the terminal C=C and Cr= C p orbitals. [38] This step is somewhat more favored for alkoxycarbenes than for aminocarbenes.…”

Reaction of substituted alkynols with alkoxycarbene complexes of chromium: a facile synthesis of substituted α,β-unsaturated-γ-butyrolactones

“…This mechanism is based on the work by Solà and co-workers. 20 In conclusion, we have described a facile synthesis of substituted racemic butyrolactones via Fischer chromium carbenes and substituted alkynols. Work is in progress toward understanding the mechanism for conversion of 3a-j to 4a-j and toward the synthesis of their optically active analogues.…”

One‐Pot Synthesis of Polysubstituted Benzenes through a N,N‐dimethyl‐4‐aminopyridine (DMAP)‐Catalyzed [4+2] Benzannulation of 1,3‐Bis(sulfonyl)butadienes and γ‐Substituted Allenoates

“…Over the past decades, various benzannulations, [4][5][6] one of the importantw ays for building substituted benzene rings, have been developed for different substituted benzenes. Among these reactions, [4+ +2] benzannulations have received much attention.…”