Mechanism of rearrangement reactions of ketenimine–4-acylfuran-2,3-dione cycloadducts—a semiempirical molecular orbital study

Abstract

Semiempirical molecular orbital calculations (AM1) are used to explain the formation of 5 as a reaction product obtained from 4-acylfuran-2,3-diones 1 and ketenimines 2. Rearrangement of the primary cycloadduct 3via intermediate 4 is found to be the most feasible pathway. An alternative fragmentation–cycloaddition mechanism via iminofurandione (9)+ ketene (10) is highly unlikely. Rearrangement of the regioisomeric primary cycloadduct 6 to 5(either directly or via intermediates 7 and 8) also requires significantly higher activation energies. The theoretical results are used to interpret previous findings from ¹⁷O isotopic labelling investigations.