Cascade synthesis of bis-N-sulfonylcyclobutenes via Cu(I)/Lewis acid-catalyzed (3+2)/(2+2) cycloadditions: observation of aggregation-induced emission enhancement from restricted C=N photoisomerization

A remarkable role of Lewis acid additives in syntheses of bis-N-sulfonylcyclobutenes via copper(I) catalyzed (3 + 2)/(2 + 2) cycloaddition cascade of sulfonyl azides and terminal alkynes is described. In addition, these cyclobutenes display a unique aggregation-induced emission enhancement (AIEE), reported for the first time, arising predominantly from restricted rotation in C=N photoisomerization in the solid state.