Synthesis of the BCD Tricyclic Core of Densanins A and B

A substrate stereocontrolled synthesis of the BCD tricyclic ring system of densanins A and B has been developed. The key transformations include the assembling of ring B via an unprecedented tandem N-allylation/SN2′ reaction and the construction of ring C via gold-catalyzed alkenylation of terminal alkyne and pyrrole.