Aliphatic diazo compounds. XII. The synthesis of 5-endo-hetero-atom-substituted 3-diazo-2-norbornanones and the proton magnetic resonance spectra of these diazo ketones and their precursors

Abstract

Treatment of 6-endo-acetoxy-5,5-dimethyl-2,3-norbornanedione (6) with tosylhydrazine gives the 2-tosylhydrazone (7), which is converted to 5-endo-acetoxy-3-diazo-6,6-dimethyl-2-norbornanone (1) by basic alumina; the exclusive formation of the 2-tosylhydrazone is ascribed to the smaller steric effect of the endo C-6 acetoxyl relative to the endo C-5 methyl group. The 6-endo-methoxy analogue of 6, 17, and the related 6-endo-chloro- and 6-endo-bromo-1,5,5-trimethyl-2,3-norbornanediones (23 and 26) are similarly converted to the corresponding α-diazo ketones 2–4. The 1H nmr spectra of the diazo ketones 1–4 have their C-1 bridgehead proton signals shifted to higher field relative to the corresponding bridgehead proton signals of the related α-diketones, whereas the C-4 bridgehead proton signals of 1 and 2 are shifted to lower field in relation to the corresponding α-diketone signals. The 1H nmr spectra of the α-diketones show an unusual long range coupling (4J ≥ 1 Hz) between the C-4 bridgehead protons and the exo C-6 protons that is significantly smaller or absent in the spectra of the related diazo ketones and monoketones. In all of these types of compound an endo-methoxyl or -acetoxyl group at C-5(6) shifts the exo and endo C-6(5) methyl signals to lower and higher field, respectively, whereas an endo-halo substituent at C-5(6) shifts both the exo and endo C-6(5) methyl signals to lower field.