Ring expansion of alkynyl cyclopropanes to highly substituted cyclobutenes via a N-sulfonyl-1,2,3-triazole intermediate

Regioselective ring expansion of alkynyl cyclopropanes to highly substituted cyclobutenes was developed. The reaction involves a copper-catalyzed cycloaddition of an alkyne with an arylsulfonyl azide and a silver-catalyzed carbene formation followed by ring expansion of a cyclopropyl carbene intermediate.