ISOMERIC 5-MEMBERED RING PHOSPHITES AND PHOSPHATES

A variety of ring- and phosphorus-substituted five-membered ring phosphites have been prepared, These materials exist as mixtures of cis and trans isomers which can be separated by glpc. The phosphites can be oxidized stereospecifically with nitrogen tetroxide to give mixtures of cis and trans phosphates which are also sep-arable by glpc. The 1H and 31P nmr spectra of these materials are reported. The 1H nmr spectra shows that the isomer present in the smallest amount in the phosphite mixtures has its ring alkyl group absorptions at lower fields than the most abundant isomer. The corresponding phosphates show much smaller differences in chemical shifts between the alkyl groups. It is suggested that the greater downfield shift of the alkyl group in the least stable phosphites is due to deshielding by the OR group on phosphorus which is cis to the alkyl group. Oxidation to the phosphates put oxygens cis to alkyl groups in both isomeric phosphates and thus deshielding occurs in either isomer. The thermodynamic equilibrium mixture of the two phosphites, 4, is 87:13. Oxidation yields the same mixture of phosphates, 12. Partial hydrolysis changes the ratio of phosphates to 61:39. This ratio does not change on further hydrolysis. These results favor a trans relationship of the ring alkyl groups and the OCH3 attached to phosphorus. Oxidation places an oxygen cis to the ring alkyl groups and thus in the phosphates steric interactions are more nearly equal than they are in the phosphites. Molecular models also support the configurational assignments. Isomeric six-membered ring phosphates are hydrolyzed without conversion into each other. © 1969, American Chemical Society. All rights reserved.