Unsaturated Four‐Membered Rings: Efficient Strategies for the Construction of Cyclobutenes and Alkylidenecyclobutanes

Abstract Our recent studies of the diastereo‐ and enantioselective formation of strained alkylidenecycloalkanes drove us to more‐thoroughly investigate the formation of four‐membered rings for which only few efficient methods are described. We first developed a strategy to diversify the saturated part of the four‐membered ring and applied it to a highly diastereoselective synthesis of more‐elaborate alkylidenecyclobutanes, which completed our precedent studies. In parallel, cyclobutene structures were built employing simple organometallic methods and further functionalized to give a diverse range of new substitution patterns, which consequently enriched the pool of cyclobutene‐based building blocks.