Synthesis and spectral characteristics of 2-aryl-6-methyl-and 2-aryl-6-benzyl-4,8a-diphenylperhydro[1,3,2]dioxaborinino[5,4-c]pyridines

Abstract

We have previously reported the synthesis of perhydro[1,3,2]dioxaborinino [5,4-c]pyridines, which are representatives of a new class of compounds containing four heteroatoms, from N-methyldiol 1a and a series of arylboronic acids 2a-f [1,2]. In the present work, we describe the synthesis of new N-methyl-and N-benzyl-2-aryl-4,8a-diphenylperhydrodioxaborninopyridines 2g-j and 3a-d from diol 1a and N-benzyldiol 1b, respectively, and arylboronic acids (Scheme 1) and examine the 1 H NMR and mass spectra of 2a-j and 3a-d. Products 2g-j and 3a-d were synthesized, similarly to 2a-f, by the tandem diesterification of piperidols 1a and 1b with arylboronic acids upon heating these compounds in toluene at reflux. These products were separated by column chromatography. Their composition and structure were supported by elemental analysis and 1 H NMR spectroscopy (Tables 1 and 2) as well as the nature of their decomposition upon electron impact (Table 3).The signal for H-4a provides the most useful information in the 1 H NMR spectra of 2g-i, 3a-b. The triplet shape of this signal and large coupling constant (10.08-11.3 Hz) suggest, by analogy with similar characteristics for the cyclohexane system, that this proton has axial orientation relative to both cis-fused rings (this has been confirmed by X-ray diffraction structural data for 2a [2]) as well as trans position relative to H-4 and H e -5 protons. The axial orientation of H-4 proton is indicated by the broad half-height width of its unresolved signal. __________________________________________________________________________________________