Spectroscopic and DFT study of 3-quinolyl-α-aminophosphonates

Spectroscopic and DFT study of two types of 3-quinolyl-alpha-aminophosphonate derivatives obtained by one-pot microwave-assisted synthesis of quinoline-3-carboxaldehyde and aniline as well as 3-aminoquinoline and benzaldehyde, respectively, with diethyl phosphite, have been described. Besides the diethyl [alpha-amino-N-(3-quinolylmethyl)]phosphonate (1) and diethyl [alpha-(3-quinolylamino)-N-benzyl]phosphonate (4) as the main reaction products, in both cases some unexpected monoester phosphonate derivatives were obtained as the by-products. In the first case along with diester 1, its corresponding monoethyl ester (2) and one monoethyl dihydrophosphonate-phosphate derivative (3) were formed, while in the second case diester 4 and a hydrogen phosphonamidate (5) were isolated. All quinoline-based alpha-aminophosphonates (1-5) have been characterized by IR spectroscopy, and the results obtained are compared and discussed with those obtained by the NMR studies. Combining experimental IR, H-1 and C-13 NMR spectra with DFT calculations, most intensive IR spectral bands of diesters 1 and 4, along with H-1 and C-13 NMR resonances of 1, 2 and 4 derivatives, were assigned. (C) 2008 Elsevier B.V. All rights reserved.