Quantum-Mechanic Investigation of the Nickel-Catalyzed [3+2+2] Cocyclization of Ethyl Cyclopropylideneacetate with two Alkynes
Abstract
The mechanism of the Ni(0)-catalyzed [3+2+2] cyclization of cyclopropyl-ideneacetate with two alkynes was investigated using the M06-2X function with two base sets def2-SVP for the main elements and def2-TSVP for the nickel atom. Only the pathway leading to the formation of 3,4- or 3,5-disubstituted products via [3+2] cocyclization was studied, with the previously proposed mechanism being reconsidered to include the return of the ligand in the final step after its removal in the initial step of the reaction. Previous studies indicate that the 2,5-disubstituted products can be formed preferentially via nickelacyclopentadienes generated by [2 + 2] cocyclization when using strongly electron-deficient alkenes. Our computational results indicate that electron-rich substituted alkenes (such as HCCSiMe3) or bulky (such as HC CtBu) lead to the formation of 3,5-disubstituted products, and the former is more active than the latter, which requires a lower activation energy of about 3.2 kcal/mol. While less-congested or simple substituted alkenes (such as HC CMe3 or (HC CPh) lead to the formation of 3,4-disubstituted products, and the former is more active than the latter ((E# = 2.6 kcal/mol). Our theoretical results agree with previous theoretical and experimental studies.
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