Convenient one-step construction of fused or zwitterionic indanes from tetraynes

A straightforward technique has been developed for the construction of fused or zwitterionic indanes <i>via</i> a one-pot, cascade hexadehydro-Diels-Alder (HDDA) reaction of different functionalized tetraynes with nucleophilic reagents (vinyl carbazole or DMSO). The reaction proceeds under mild conditions with no metal catalysts, bases, or oxidants and exhibits excellent regioselectivity and high yields. A plausible reaction mechanism for the formation of zwitterionic indanes is proposed based on literatures and isolated fused indanes.