Journal
DALTON TRANSACTIONS
Volume 40, Issue 1, Pages 211-224Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c0dt00881h
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- Deutsche Forschungsgemeinschaft
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A facile synthesis of functionally substituted 2-(hetero)aryl 1,3-benzazaphospholes via nickel-or palladium-catalyzed phosphonylation of N-acyl-2-bromoanilides 1a-k with triethyl phosphite is presented. Anilidophosphonates 2a-g with naphthoyl-, o-substituted phenyl, furoyl-or thenoyl groups allow direct reductive cyclization with LiAlH4 to benzazaphospholes 3. The reaction of the o-bromoderivative 2d proceeds with concomitant replacement of bromine by hydrogen, whereas the electron-withdrawing pyridyl group of 2h prevents the synthesis of 3h by this short route. An alternative synthesis of 2-pyridylbenzazaphosphole 3h via anilidophosphonates succeeded starting from Fmoc-anilinophosphonate 2k via selective cleavage of the N-protecting group, reduction of the resulting phosphonoaniline to phosphinoaniline and cyclization with pyridine-2-carboxaldehyde via a dihydrobenzazaphosphole 8. N-Substituted pyridylmethylbenzazaphosphole 9 was detected as a side product. The structure elucidation of the new compounds is based on multinuclear NMR data and X-ray crystal structure analyses of a phosphonoanilide, underlining the dominance of N-H center dot center dot center dot O=P hydrogen bonds over N-H center dot center dot center dot O=C type hydrogen bonds, of 3h and a supramolecular associate of 3b and its unprecedented air oxidation product 10.
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