Synthesis and Conformational Analysis of Saturated3,1,2‐Benzoxazaphosphinine 2‐Oxides

N ‐Unsubstituted, N ‐methyl and N ‐benzyl cis‐ and trans ‐2‐(hydroxymethyl)cyclohexylamines were subjected to ring closure with phenylphosphonic dichloride, phenyl dichlorophosphate and bis(2‐chloroethyl)phosphoramidic dichloride in order to synthesize P ‐epimeric diastereomers of the corresponding unsubsituted and N ‐substituted 2‐phenyl‐, 2‐phenoxy‐ and 2‐[bis(2‐chloroethyl)amino]octahydro‐2 H ‐3,1,2‐benzoxazaphosphinine 2‐oxides. The stereochemistry and conformations of the prepared compounds were analyzed mainly by variable‐temperature 1 H, 13 C and 31 P NMR spectroscopy. Geometry optimizations were performed for some trans ‐fused molecules by utilizing the B3LYP DFT method and a locally dense basis set, followed by J H,P coupling constant calculations at the UB3LYP/cc‐pVTZ level of theory. The population of the N‐out conformation of the cis ‐fused compounds was found to increase with increasing steric size of the N substituent (H < Me < CH 2 Ph), and also to be strongly influenced by the configuration at the phosphorus atom. The heteroring of the trans ‐fused compounds predominantly adopts a chair conformation with the notable exception of the (2 R *,4a S *,8a S *) epimers of the 2‐phenoxy‐substituted compounds, for which the axial tendency of OPh causes the heteroring to adopt mainly B 2,4a ‐ and/or 1 S 4a ‐type nonchair conformations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)