Cascade C-H bond functionalizations of benzoyl acetonitriles/methylsulfones with cyclic 2-diazo-1,3-dicarbonyl compounds: An efficient access to diversely functionalized naphtho[1,8-bc]pyrans

In this paper, a Rh(Ill)-catalyzed cascade reaction of benzoyl acetonitriles/methylsulfones (1) with cyclic 2-diazo-1,3-dicarbonyl compounds (2) leading to a convenient and efficient preparation of diversely functionalized naphtho[1,8-bc]pyrans is presented. Mechanistically, the formation of the title compounds involves a cascade process including: 1) C(sp(2))-H/C(sp(3))-H bonds cleavage, metalation and carbeniod insertion of I with 2 followed by an intramolecular annulation to afford substituted 1-naphthol as a key intermediate; 2) C(sp(2))-H/O-H bonds cleavage, metalation and carbeniod insertion of the in situ formed 1-naphthol intermediate with 2 followed by an intramolecular cyclization to give the naphtho [1,8-bc]pyran product. Compared with literature methods for the synthesis of naphtho[18-bc]pyran derivatives, this new protocol has advantages such as simple operational procedure, easily obtainable substrates, high efficiency and excellent atom-economy. (C) 2018 Elsevier Ltd. All rights reserved.