1,1′-SPIROBIINDANES

The product from both the acid-catalyzed cyclodehydration of 4-methyl-4-phenyl-2-pentanone (1a) described by Hoffman (1) and by Barnes and co-worker (2) and the reaction of the saturated cyclic dimer of α-methylstyrene with aluminum chloride reported by Adams and co-workers (3) was shown to be 3,3,3′,3′-tetramethyl-1,1′-spirobiindane (IXa) by Curtis (4). A mechanism is postulated to explain the formation of the 1,1′-spirobiindane system. The reactions of several polyalkylindenes with α-methylstyrene and triphenylcarbinol were investigated. Several new polyalkyl-1,1′-spirobiindanes and a new polyalkylindene[1,2-a]indene were produced. Two of the 1,1′-spirobiindanes investigated were synthesized by unequivocal methods.