Design and synthesis of a hybrid framework of indanone and chromane: total synthesis of a homoisoflavanoid, brazilane.

A chemical backbone of tetracyclic homoisoflavanoid natural products such as brazilin inspired us to design a new chemical scaffold, 6a,11b-dihydroindeno[2,1-c]chromen-7(6H)-one, which is a hybrid structure of indanone and chromane. Pd-catalyzed Suzuki-Miyaura cross-coupling of 4-chloro-2H-chromene-3-carbaldehydes with (hetero)aryl boronic acids was employed as a means to introduce a wide variety of (hetero)aryl groups as the D ring and intramolecular Friedel-Crafts acylation was utilized to construct the C ring of this skeleton. Total synthesis of the natural product, brazilane, was also demonstrated via this new chemical framework.