Theoretical study of [3+3] annulation reaction of bromoenal with β-tetralone catalysed by N-heterocyclic carbene

N-heterocyclic carbenes (NHCs) are effective organocatalysts, which are widely used in various cycloaddition reactions. Among them, the [3 + 3] cycloaddition reaction type can be used for the synthesis of six-membered ring, which is also one of the most important methods for the formation of carbon-carbon bonds in organic chemistry. In this paper, a possible reaction pathway for the stereoselective [3 + 3] cycloaddition of bromoenal and beta-tetralone have been investigated at the M06-2X/6-31G(d,p)/IEFPCM(THF) level. Our suggested mechanism includes binding of the NHC to bromoenal, 1,2-proton transfer, debromination, 1,3-proton shift, Michael addition, protonation, deprotonation and cyclisation, and NHC regeneration. The stereochemistry of the reaction is determined by the Michael addition step, and the favourable pathway generates the R-configurational dihydropyranone. Furthermore, through the use of global reactivity indexes (GRIs), we are able to demonstrate that the nucleophilicity of the bromoenal is increased by the NHC. The mechanistic insights gained in this work should be helpful in the rational design of potential catalysts for analogous reactions.