Hexamethyl bicyclo hexa-2,5-diene

Bicyclo[2.2.0[hexadiene, hexamethyl-[Bicyclo[ 2.2.0] hexa-2,5-diene,... 

Palladium Dichloro-( j4-hexamethyl-bicyclo[2.2.0]hexa-2,5-dien)-E17f, 926 (Komplex-Synth.)... 

Metal-catalyzed decomposition of diazomethane in the presence of 1,2,3,4,5,6-hexamethyl-bicyclo[2.2.0]hexa-2,5-diene (11, hexamethyl Dewar benzene) has been shown to give the simple or double cycloaddition products with exo configuration. When the reaction was carried out in the absence of a metal catalyst, the products of C-H insertion to allylic C-H bonds were also observed, in addition to cycloaddition to the double bond to an extent of 25%. A C-C insertion reaction at the unusually long central bond of hexamethyl Dewar benzene was not detected. The reaction conditions were designed to generate methylene in the singlet state, and the observed products were those that would be expected for the reaction of singlet methylene with hexamethyl Dewar benzene. 

The first ir complex of the Dewar benzene system was prepared by Fischer et al. (202) by reaction of (CH3CN)3Cr(CO)3 with hexamethyl-bicyclo[2.2.0]hexa-2,5-diene. The monomeric, yellow, crystalline complex (CigHialC r(CO)4 has an NMR spectrum with two sharp absorptions at T values of 8.26 and 9.1 ppm with relative intensities of 2 1. Structure (18), originally assigned on the basis of spectral data, has been confirmed... 

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