Controllable [2+2] Cycloadditions of 1,5‐Bisallenyl‐Substituted Compounds

Come on allenes: [2+2] Cycloadditions of 1,5-bisallenyl compounds were realized in controllable head-to-head and tail-to-tail manners, resulting in the formation of [3.2.0] and [5.2.0] bicyclic compounds, respectively (see scheme). The bicyclic compounds include double bonds suitable for further elaboration and thus these reactions may be powerful tools in organic synthesis.