- Organophosphorus Compounds. XIX. Synthesis of 2,3-Dihydro-1H-1,2-benzazaphosphole 2-Oxides, Variously Substituted on Nitrogen and Phosphorus, by N-P Cyclization of Zwitterionic Intermediates
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2-Phenyl-2,3-dihydro-1H-1,2-benzazaphosphole 2-oxide (7a) was prepared by thermolysis of the corresponding zwitterionic amino phosphinic acid (4), or its hydrochloride salt (1).Thermolysis of methyl (2-aminobenzyl)phenylphosphinate (5a) was accompanied by intermolecu;ar O->N transmethylation to give, after cyclization, 1-methyl-2-phenyl-2,3-dihydro-1H-1,2-benzazaphosphole 2-oxide (9a); similarly, the ethyl ester (5b) gave the N-ethyl heterocycle (9b). Reaction of 2-phthalimidobenzyl bromide (13a) with diethyl methylphosphonite (14b) gave ethyl (2-phthalimidobenzyl)methylphosphinate 15a).Hydrolysis of (15a) afforded (2-aminobenzyl)-methylphosphinic acid (16), and thermolysis of this produced 2-methyl-2,3-dihydro-1H-1,2-benzazaphosphole 2-oxide (18a). 1-Methyl-2-methoxy-2,3-dihydro-1H-1,2-benzazaphosphole 2-oxide (24) was synthesized in an analogous manner. Base catalyzed N-alkylation of the benzazaphosphole derivatives (7a) and (18a) was readily achieved, and the interconversion of 2-oxides and 2-sulfides was accomplished by conventional methods.
- Collins, David J.,Drygala, Peter F.,Swan, John M.
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p. 2517 - 2536
(2007/10/02)
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