Synthesis,spectroscopic and configurational study,and ab initio calculations of new diazaphospholanes

New 2-substituted diazaphospholane-2-oxides (I-III, V-VIII) and diazaphosphorinane-2-oxide (IV) were synthesised and characterised by ¹H, ¹³C, and ³¹P NMR, IR spectroscopy, and elemental analysis. The presence of chiral diamino groups in compounds II and V–VIII gives rise to various diastereomers so that the ³¹P{¹H} NMR spectra demonstrated three and two peaks with different ratios, respectively. Also, the ¹H and ¹³C{¹H} NMR spectra of compounds II and V–VIII revealed three and two sets of signals for the related conformers (diastereomers). Interestingly, the ³¹P NMR spectrum of V in D₂O indicated a great upfield shift (Δδ = 19.0) for ³¹P relative to the value obtained in DMSO-d₆ (solvent effect). The two signals in V split further to three signals in the presence of β-cyclodextrin. Moreover, conformational analysis of diazaphospholane V was studied by ab initio calculations at the HF and B3LYP levels of theory using the Gaussian 98 program. Results indicated that among four suggested diastereomers (C1–C4) of V, C1 and C3 containing methyl group in the equatorial position are the most stable forms.