Abstract
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)