Synthesis and stereogenic properties of N,N-spiro bridged bis(cyclotriphosphazene) compounds containing two equivalent chiral centres

Abstract

The stereogenic properties of N,N-spiro bridged bis(cyclotriphosphazene) compound having four potential stereogenic phosphorus centres have been investigated. Two reaction pathways, in which same reactions were done in different order, were used to determine the isomer variety and to compare them. When the first route included unsymmetrically substitution (2-methylaminoethanol), aminolysis (n-butylamine) and deprotonation (sodium hydride) reaction steps, respectively, the second route consisted of aminolysis (n-butylamine), deprotonation (sodium hydride) and unsymmetrically substitution (2-methylaminoethanol) reaction steps, respectively. Both routes resulted in formation of the same products (4a and 4d) containing two equivalent chiral centres. The structures and stereogenic properties of the products, 4a and 4d were characterized by X-ray crystallography and 31P NMR spectroscopy on addition of the chiral solvating agent which is (R)-(+)-2,2,2-trifluoro-1-(9-anthryl)ethanol. These new di-spiro derivatives (4a and 4d) bring about trans–trans and cis–cis geometric isomers and they are meso due to centre of the symmetry and plane of the symmetry.