Novel domino reactions in β-carbolines with triple bonded dienophiles
摘要:
Vinylpyrrolo-[2,1-a]-beta-carbolines 1 give different products upon reaction with dienophiles. With dimethyl acetylenedicarboxylate (DMAD), a novel domino process takes place, involving Michael attack and rearrangement, affording complex polycycles like 3, 4, and S. Diels-Alder cycloadditions are favored in the presence of Lewis acids and are the only reactions with dimethyl maleate. When 3-butyn-2-one is used as dienophile, a Stevens rearrangement is observed giving product 9. (C) 2008 Elsevier Ltd. All rights reserved.
Functionalization of beta-carbolines is a challenge as numerous natural alkaloids with different biological activities present this heterocycle. The RCM is used herein with allyl-, vinyl-, ethynyl-, and propargyl-beta-carbolines to generate additionally fused hetero- and carbocycles, and it is combined with other cyclization processes to achieve great molecular complexity in one synthetic step. Thus, an RCM-Diels-Alder sequence gives pentacyclic Compounds related with certain alkaloids. On the other hand, vinyl-pyrrolo[2,1-a]-beta-carbolines and vinyl-beta-carbolines give different products upon reaction with activated dienophiles. Thus, a novel domino processes affords complex polycycles like 35-38. Other alkynes like 3-butyn-2-one give a Stevens rearrangement. (C) 2009 Elsevier Ltd. All rights reserved.
Novel domino reactions in β-carbolines with triple bonded dienophiles
Vinylpyrrolo-[2,1-a]-beta-carbolines 1 give different products upon reaction with dienophiles. With dimethyl acetylenedicarboxylate (DMAD), a novel domino process takes place, involving Michael attack and rearrangement, affording complex polycycles like 3, 4, and S. Diels-Alder cycloadditions are favored in the presence of Lewis acids and are the only reactions with dimethyl maleate. When 3-butyn-2-one is used as dienophile, a Stevens rearrangement is observed giving product 9. (C) 2008 Elsevier Ltd. All rights reserved.