Sir :Considering the amount of work which has been reported on norcaradiene-cycloheptatriene equilibria in general,' and specifically on the structures of Buchner's esters, we were surprised to find two new adducts of carbomethoxycarbene and benzene, i.e., the 2 : 1 and 3 : l adducts, 1 and 2. We are prompted to report 1 2 their preparation and stereochemistry now by recent reports of other bis-and trishomobenzene derivatives.3The synthetic procedure consists of slowly adding (24 hr) a solution of 20 g of methyl diazoacetate in 50 ml of benzene to 50 ml of refluxing benzene containing 0.5-1.0 g of finely powdered copper-bronze. After evaporation under vacuum of the volatile components of the reaction mixture (benzene, dimethyl fumarate, dimethyl maleate, and methyl cycloheptatriene-7-carboxylate), the 2: 1 and 3 : 1 adducts were isolated by column chromatography of the residual oil (Silica gel,The 2 : 1 adduct, dimethyl tricyclo[5.1 .0.02b4]oct-5ene-3,8-dicarboxylate (l), mp 130-132", was isolated in 3% yield and was shown to have the structure and stereochemistry indicated by the following observat i o n~.~ The nmr spectrum (CDCI,) showed two olefinic protons as an apparent triplet at 6 5.70, six methoxy protons as a singlet at 3.65, and a complicated multiplet of six protons at 1.5-2.2. The proton ratios indicate a tricyclic skeleton, and the magnetic equivalence of the olefinic protons and the methoxy protons suggested a symmetrically substituted (exo,exo-or endo,endo-) tricyclo[5.1 .0.02~4]oct-5-ene. Double irradiation at 6 1.6 caused the olefinic triplet to collapse to a singlet, and, conversely, irradiation at 5.7 simplified the highfield signals allowing analysis of the region as two identical ABC systems: Ha, 6 2.12; Hb, 1.78; H,, 1.63; the small values of the coupling constants Jab and Jbc,6CC14-CHC13). J a b = 3.9 HZ, Jac = 8.6 HZ, J b c = 4.0 H z .~ Based on , J. Amer. Chem. Soc., 93, 3837 (1971).(4) Satisfactory elemental analyses and mass spectral molecular weights have been obtained for all new compounds reported. The nmr spectra reported were recorded on a Varian A-60, (5) Parameters refined by L A O C N~ spectral analysis program of A. A.