Novel chemistry of β-carbolines. Expedient synthesis of polycyclic scaffolds

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.