Conformational study of some saturated 2-[bis(2-chloroethyl)amino]-1,3,2-benzoxazaphosphorinane 2-oxides

Conformational analyses of cis-and trans-fused 2-[bis(2-chloroethyl)amino]-3,4,4a,5,6,7 octahydro-1,3,2-benzoxazaphosphorinane 2-oxides and their 3-methyl and 3-benzyl derivatives were performed by H-1, C-13, P-31, and variable-temperature NMR methods. Depending on the P-2 configuration and the substituent on N-3, different equilibria between chair-chair and chair-twist-boat conformations were found for the trans-fused isomers. The N-3 substituent shifts the equilibrium toward the chair-twist-boat to an extent varying in the sequence methyl > benzyl > hydrogen. In the cis-fused isomers, the nature of the N-3 substituent affects the equilibrium between the O-in and O-out conformations in the same sequence.