Abstract
The oxyvinylcyclobutanes (2), photoadducts of the dioxopyrrolines (1) to trimethylsilyloxybutadienes, undergo two different types of skeletal rearrangements depending on the reaction conditions. Thermolysis of 2 caused expansion of the cyclobutane ring by a 1, 3-shift of the C1-C7 bond toward the vinyl group, giving rise to the hydroindoles (3) in moderate yields. This 1, 3-shift was enormously accelerated when an alkoxide was generated by the action of tetrabutylammonium fluoride (TBAF) on trimethylsilyloxyvinylcyclobutanes. Thus, 2a-d, on treatment with TBAF at -30°C, provided hydroindole derivatives in good yields, though in some cases (2a, b) accompanied with by-products (10). This demonstrates that the [2+2] photoannulation of dioxopyrroline, when coupled with the anionic 1, 3-shift, provides an efficient synthetic route to functionalized hydroindoles. Under acidic conditions, the oxyvinylcyclobutanes(2) rearranged to give exclusively the 2-azatricyclo[4.3.0.04, 9]nonanes (10), whose formation was rationalized in terms of the intramolecular Prins-type cyclization with concomitant expansion of the cyclobutane ring by 1, 2-shift of the C1-C7 bond toward the vinyl group.
