Structures of the 2:1 adducts of benzyne with 2-methylanisole and benzene

Abstract

The 2:1 adduct of benzyne with 2-methylanisole is shown to have the bisbenzotricyclic structure 6,6a,11,11a-tetrahydro-5-methoxy-6-methyl-5,6,11-metheno-5H-benzo[a]fluorene by a single-crystal X-ray diffraction study (C20H18O: Pca21, a = 15.0497(17), b = 9.87783(11), c = 9.6846(11); Z = 4; 1672 data points, R1 = 0.0325). This structure is compared to an unpublished crystal structure of the parent hydrocarbon 6,6a,11,11a-tetrahydro-5,6,11-metheno-5H-benzo[a]fluorene, C18H14. Both structures have also been computed by DFT methods at the B3LYP/6-311(d,p) level of theory. Bond distances and angles between the solid-state measurements and gas-phase calculations are found to agree well; average deviations are well below 1%. The 1H NMR spectra show surprisingly small 3JHH couplings in the central tricyclic cage, but can be assigned using 2D spectroscopy.Key words: Hydrocarbon cages, strained rings, cyclopropane, X-ray crystallography, NMR.