Acceleration of hetero-Michael reaction by symmetrical pentacyclic guanidines

Symmetrical pentacyclic guanidines 1a–c and 2 which contain the core skeleton of 13,14,15-isocrmbescidine 800, have been synthesized. In the presence of catalytic amounts of these guanidines 1, the reaction rate of the conjugate addition of pyrrolidine (9) to γ-crotonolactone (10) could be enhanced depending upon the size of the cavities and substituents on tetrahydropyran rings of 1 and 2.