Reactivity of cis-fused 3-(dialkylamino)cyclobutenes in polar and apolar solvents. Synthesis, x-ray structures, and reactions of cis,cis- and cis,trans-1,3-cycloalkadienes
[2+2]-Cycloadducts of enamines and DMAD, formed in apolar solvents, isomerize to pyrrolizine derivatives under mild conditions in protic polar solvents like methanol and 1-butanol.