Unexpected formation of highly strained 2,5-Dioxa-3-Silabicyclo[2.1.0]pentane by the reaction of isolable dialkylsilylene with Benzil

The reaction of isolable dialkylsilylene 1 with benzil gave [1+4] cycloadduct 1,3-dioxa-2-sila-cyclopent-4-ene 2 and unexpected 2,5-dioxa-3-silabicyclo[2.1.0]pentane derivative 3. Compound 3 slowly isomerized to 2. The global reaction route mapping method of the model compounds suggests that three reaction paths from an initial silylene-ketone complex (carbonyl silaylide) to 2. A large ring strain energy of model compound for 3 (3) (218.9 kJ·mol^-1) was estimated by density functional theory calculations.