APPROACHES TO PSEUDOINDENE. PRODUCTS DERIVED FROM THE CARBENES BENZOCYCLOBUTENE-1-YLCARBENE, 2-METHYLBENZOCYCLOBUTENYLIDENE AND o-STYRYLCARBENE

Article abstract of DOI:10.1016/S0040-4020(01)97701-4

The title carbenes, which in principle can all serve as precursors to the reactive hydrocarbon pseudoindene, have been generated by the photolysis of the sodium salts of the tosylhydrazones of (a) benzocyclobutene-1-carboxaldehyde, (b) 2-methylbenzocyclobutenone and (c) o-formylstyrene.Indene was formed in reactions (a) and (c): in the former case deuterium labelling experiments suggest a ring expansion mechanism rather than a pseudoindene intermediate.In the letter case deuterium labelling and trapping experiments implicate a symmetrical isoindene intermediate, which can arise either via pseudoindene, or via direct electrocyclic ring closure o-styrylcarbene.