P=C-N-heterocycles: synthesis of biaryl-type 1,3-benzazaphospholes with ortho-substituted phenyl or 2-heteroaryl groups.
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 LiAlH(4) 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 3hvia anilidophosphonates succeeded starting from Fmoc-anilinophosphonate 2kvia 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···O=P hydrogen bonds over N-H···O=C type hydrogen bonds, of 3h and a supramolecular associate of 3b and its unprecedented air oxidation product 10.
Institut für Biochemie, Anorganische Chemie, Ernst-Moritz-Arndt-Universität Greifswald, Felix-Hausdorff-Str. 4, D-17489, Greifswald, Germany.
Bhaskar Reddy
BR
Aluri
Basit
B
Niaz
Markus K
MK
Kindermann
Peter G
PG
Jones
Joachim
J
Heinicke
D003500:Cyclization; D006571:Heterocyclic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D017553:Phosphorus Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization
D006571:Heterocyclic Compounds; D017553:Phosphorus Compounds