Efficient Synthesis and Spectroscopic Analysis of 8-Nitro Spiro C-3-Annulated 2-Benzazepines and their N-Oxides

Abstract

Nitroderivatives 9a-g have been prepared with great C-8 regioselectivity by allowing the corresponding 1,2,4,5-tetrahydrospiro[3H-2-benzazepine-3,1"-cycloalkanes] 8a-g to react with potassium nitrate and concentrated H₂SO₄. The oxidative reaction of a nitrogen-carbon bond in spirobenzazepines 8 and 9 was performed with H₂O₂ and catalytic amounts of sodium tungstate at room temperature affording nitrones 10a-d in moderate to high yields. Stereochemical assignments for all the 2-benzazepine derivatives obtained were derived from a full analysis of the ¹H NMR spectroscopic data and an X-ray crystallographic analysis of 1,5-dimethyl-8-nitro-1,2,4,5-tetrahydrospiro[3H-2-benzazepine-3,1"-cyclohexane] 9c. These data indicate that the 2-benzazepines 8-11 in solution present the azepine ring preferably in the chair conformation, with the methyl substituent at C-5 disposed equatorially.

Key words

2-benzazepines - regioselective nitration - homoallyl-amines - nitrones

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Atomic coordinates for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Centre. The coordinates can be obtained, on request, from the Director, Cambridge Crystallographic Centre, 12 Union Road, Cambridge CB2 1EZ, UK.