Enantioselective Cyclobutenylation of Olefins Using <i>N</i>-Sulfonyl-1,2,3-Triazoles as Vicinal Dicarbene Equivalents

Abstract

Cyclobutenes are highly useful synthetic intermediates as well as important motifs in bioactive small molecules. Herein, we report a regio-, chemo-, and enantioselective synthesis of cyclobutenes from olefins using <i>N</i>-sulfonyl-1,2,3-triazoles as vicinal dicarbene equivalents or alkyne [2 + 2] cycloaddition surrogates. Terminal and <i>cis</i>-olefins can be transformed into enantioenriched cyclopropanes via rhodium catalysis. Then, in one pot, treatment of these intermediates with tosyl hydrazide and base effects diazo formation followed by rhodium-catalyzed ring expansion to yield enantioenriched cyclobutenes. These cyclobutenes can be transformed into highly substituted, enantioenriched cyclobutanes, including structures relevant to natural product scaffolds.