CONFORMATIONAL STUDY OF SOME SATURATED (2-CHLOROETHYL)AMINO]-1,3,2-BENZOXAZAPHOSPHORINANE 2-OXIDES

Conformational analyses of cis-and trans-fused 2-[bis(2-chloroethyl)am ino]-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 config uration and the substituent on N-3, different equilibria between chair -chair and chair-twist-boat conformations were found for the trans-fus ed isomers. The N-3 substituent shifts the equilibrium toward the chai r-twist-boat to an extent varying in the sequence methyl > benzyl > hy drogen. In the cis-fused isomers, the nature of the N-3 substituent af fects the equilibrium between the O-in and O-out conformations in the same sequence.