2,4,6,8-TETRACARBOMETHOXYBARBARALANE

2,4,6,8-Tetracarbomethoxybarbaralane has been synthesized in four step s from malondialdehyde and dimethyl 1,3-acetonedicarboxylate. The P2I4 -induced Grob fragmentation (Kuhn-Winterstein reaction) of hoxytetracy clo[3.3.1.0(2,8).0(4,6)]nonane-3,7-exo, exo-diol gave in addition to 2 ,4,6,8-tetracarbomethoxybarbaralane (36%), two side products identifie d as 2,4,6-tricarbomethoxybarbaralane (3%) and 6,8-tetracarbomethoxybi cyclo[3.3.1]nona-2,6-diene, a dihydrobarbaralane (2%). 2,4,6,8-Tetraca rbomethoxybarbaralane was shown to undergo a rapid degenerate Cope rea rrangement in solution with an activation energy of Delta G(158) = 5. 95 +/- 0.2 kcal/mol, 1.53 kcal/mol lower than that for barbaralane its elf. In the solid state the molecule proved to be static on the basis of its CP-MAS C-13 NMR spectrum. The X-ray structure of 2,4,6,8-tetrac arbomethoxybarbaralane shows a cyclopropane bond of 1.61 Angstrom (C-2 -C-8) and an open-end distance of = 2.40 Angstrom (C-4-C-6). The equil ibrium for the tricarbomethoxybarbaralane was found to been the side o f the 2,4,6-isomer, on the basis of its spectral data. The X-ray struc ture confirmed this for the solid state. These findings are in agreeme nt with theoretical expectations.