An Approach to Bis(amino Acid)s Utilizing Dimethyl 2,4-bis(diazo)-3-oxoglutarate and Studies of Tris(2,6-dihydroxyphenyl)e, E = B, P.

Abstract

When treated with a diazo transfer agent, dimethyl 3-oxoglutarate afforded a high yield of the bis(diazo) compound dimethyl 2,4-bis(diazo)-3-oxoglutarate, 33. The bis(diazo) compound, catalyzed by Rh2(OAc)4, reacted with an excess of O-benzyl carbamate, (CbzNH2), to give the product of double N-H insertion, 36, [MeO2C-CH(NHCbz)]2C=O. Thus in two steps one obtains a protected bis(amino acid). Compound 36 exhibits complex 1H and 13C NMR spectra, which may be rationalized by assuming 36 is predominantly enolic. Attempted removal of the Cbz protecting groups gave startling results. Hydrogenation of 36 over Pd/C led to dimethyl 2-carboxamidosuccinate, 44, MeO2CCH2CH(CONH2)(CO2Me), the structure of which was proven by x-ray crystallography. In other studies, tris(2,6-dimethoxyphenyl)boron was synthesized by literature procedures. Demethylation was attempted using AlCl3/toluene, and BBr3•SMe2. In both cases, resorcinol, the product of B-C bond cleavage was observed. Tris(2,6-dihydroxyphenyl)phosphonium chloride 63 was synthesized and its x-ray crystal structure was determined. It binds ethyl ether via a hydrogen bond. The three aryl rings adopt propeller symmetry, with torsion angles relative to the P-H direction of 20.5°, 24.5°, and 30.8°. Compared to the average C-P-H angle of [Ph3PH]+ - 108.2°, the average C-P-H angle of 63 is smaller, namely 104.9°.