Tandem Cope-rearrangement and [2+2] cycloaddition of cis-1,2-diethynylcyclopropane and its mono-hetero analogues: A DFT investigation

Publication date: Available online 2 December 2017 Source:Computational and Theoretical Chemistry Author(s): Manjinder Kour, Raakhi Gupta, R.K. Bansal Tandem Cope-rearrangement and [2+2] cycloaddition of cis-1,2-diethynylcyclopropane and its mono-hetero analogues (hetero atom: N, O, P) have been investigated in the gas phase at the B3LYP/6–31+G(d) level. The activation enthalpies for the Cope rearrangement of these compounds range from 24.18 to 29.60 kcal mol-1 which are 4-9 kcal mol-1 higher than those for the Cope rearrangement of the corresponding divinyl-analogues, which can be attributed to the cyclic strain being induced by the developing bis-allenic structure resulting from the Cope rearrangement of the former. However, the same bis-allenic moiety accelerates [2+2] cycloaddition of the initially formed intermediate bringing down the activation enthalpies to 2.03 to 9.63 kcal mol-1 only; in the case of cis-1,2-diethynyloxirane, it is barrierless. The CASSCF calculations indicate that [2+2] cycloaddition occurs preferably via a concerted mechanism. The final products, bicyclo[3.2.0]hepta-1,4,6-triene and its mono-hetero analogues are stabilized due to 6π electrons delocalization. Graphical abstract

Source: Computational and Theoretical Chemistry - December 2, 2017 Category: Chemistry Source Type: research