Acceleration of hetero-Michael reaction by symmetrical pentacyclic guanidines
摘要:
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 gamma -crotonolactone (10) could be enhanced depending upon the size of the cavities and substituents on tetrahydropyran rings of 1 and 2. (C) 2001 Elsevier Science Ltd. All rights reserved.
Acceleration of hetero-Michael reaction by symmetrical pentacyclic guanidines
摘要:
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 gamma -crotonolactone (10) could be enhanced depending upon the size of the cavities and substituents on tetrahydropyran rings of 1 and 2. (C) 2001 Elsevier Science Ltd. All rights reserved.
Studies directed toward the total synthesis of pinnatoxin A: synthesis of the 6,5,6-dispiroketal (BCD ring) system by double hemiketal formation/hetero-Michael addition strategy
An efficient, highly stereoselective synthesis of the C10–C26 portion of pinnatoxin A has been achieved, wherein the key step is a highly stereoselective construction of the 6,5,6-dispiroketal (BCD ring) system by an intramolecular hetero-Michael addition of a hemiketal alkoxide reversibly formed under the influence of lithium methoxide.