A copper-catalyzed diastereoselective cross 3+3 dipolar cycloaddition of ethynyl methylene cyclic carbamates with N,N'-cyclic azomethine imines has been realized. The presence of an extended C═C bond in N,N'-cyclic azomethine imines distinctively changes the reaction pathway, enabling the precise regioselective control of ethynyl methylene cyclic carbamates serving as C1,C3-dipoles rather than sterically favorable C1,N-ones, thus delivering a range of N-(7-ethynyl-3-oxo-7-phenyl-8-((E)-styryl)-2,3,7,8-tetrahydro-1H-pyrazolo1,2-apyridazin-6-yl)benzenesulfonamides in up to 93% yields.
Li et al. (Fri,) studied this question.