A base-promoted cascade 5-exo-dig cyclization/carboxylation of o-alkynylsulfamides with CO2 has been accomplished, furnishing a variety of benzosultam-containing acrylates in good yields by using CO2 as the carboxylic source. Notably, in the case of substrates bearing a TMS-alkyne motif, the gem-dicarboxylation products were generated unprecedentedly.