Construction of spirocarbocyclic scaffolds through dearomatization using calcium carbide as an alkyne source

A novel method for the one-step construction of spirocarbocyclic scaffolds by dearomatizing annulation is described. A number of spiro[indene-1,1'-naphthalen]-2'-ones are efficiently synthesized by reactions of 1-arylnaphthalen-2-ols with aryl iodides and calcium carbide through Csp²-H activation and simultaneous formation of four C-C bonds. Meanwhile, a series of spiro[cyclopentane-1,1'-naphthalene]-2,4-dien-2'-ones are effectively obtained by reactions of 1-bromonaphthalen-2-ols with aryl iodides and calcium carbide through cross-coupling and simultaneous formation of seven C-C bonds. The salient feature of this protocol is the use of an inexpensive and easy-to-handle solid alkyne source as a substitute for flammable and explosive gaseous acetylene. In addition, satisfactory yields and a simple workup procedure are also advantages of this method. The corresponding products can also be synthesized on a gram scale.