KINETIC ISOTOPE EFFECTS ON METAPHOSPHATE GENERATION FROM FRAGMENTATION OF 2,3-OXAPHOSPHABICYCLO[2.2.2]OCTENE DERIVATIVES

Kinetic isotope effects of deuterium and oxygen-18 were measured on fr agmentation of syn-3-ethoxy (la) and syn-3-(N, N-diethylamino) (1b) 2, 3-oxaphosphabicyclo[2.2.2]octene derivatives in 1,2-dichloroethane at 100 degrees C. The secondary deuterium isotope effect on hydrogen adja cent to the P-C bond was found to be 1.060 +/- 0.008 for 1a and 1.081 +/- 0.009 for 1b. The kinetic oxygen isotope effect on the bridge P-O- C is 0.9901 +/- 0.0016 for 1a. The data indicate an unsymmetrical tran sition state for retrocycloaddition extrusion of the metaphosphate moi ety, with the breakage of the C-P bond and formation of the P = O bond more advanced than the C-O breakage. A synthesis of la and Ib labeled with deuterium is described. (C) 1996 John Wiley & Sons, Inc.