Abstractmagnified imageThe reactive zwitterionic 1 : 1 intermediate 6 generated in situ from the reaction between an isocyanide 2 and a dialkyl acetylenedicarboxylate (=dialkyl but‐2‐ynedioate) 3 was trapped by an N‐arylmaleimide or ‐phthalimide 4 to produce a highly functionalized 1‐oxa‐6‐azaspiro[4.4]nona‐3,8‐diene‐3,4‐dicarboxylate 5 in excellent yield (Scheme and Table).
Abstractmagnified imageThe reactive zwitterionic 1 : 1 intermediate 6 generated in situ from the reaction between an isocyanide 2 and a dialkyl acetylenedicarboxylate (=dialkyl but‐2‐ynedioate) 3 was trapped by an N‐arylmaleimide or ‐phthalimide 4 to produce a highly functionalized 1‐oxa‐6‐azaspiro[4.4]nona‐3,8‐diene‐3,4‐dicarboxylate 5 in excellent yield (Scheme and Table).