Reaction of Tetramethyl-1,2-dioxetane with Phosphines: Deuterium Isotope Effects

Article abstract of DOI:10.1021/jo00179a010

The reaction of tetramethyl-1,2-dioxetane (1) in C6D6 with methyldiphenylphosphine (2a), methyl-d3-diphenylphosphine (2d), dimethylphenylphosphine (2c), and dimethyl-d6-phenylphosphine (2d) produced the corresponding 2,2-dihydro-4,4,5,5-tetramethyl-2,2,2-trisubstituted-1,3,2-dioxaphospholanes 3a-d in 90percent yield or better.The phosphoranes were characterized by 1H and 31P NMR spectroscopy and by their thermal decomposition (60 deg C) to tetramethyloxirane and the corresponding phosphine oxides .Kinetic studies of the rate of phosphorane formation in benzene were carried out by the chemiluminescence method.The reaction was found to be of the first order with respect to 1 and to the phosphines.Inverse deuterium isotope effects were observed for the reaction of 1 with phosphines 2a-d.The value of k_CH3/k_CD3 obtained with phosphines 2a,b was found to be 0.94 +/- 0.01 while that with phosphines 2c,d was found to be 0.91 +/- 0.01.The rates of phosphorane formation for the reaction of tetramethyl-d12-1,2-dioxetane (1d) with 2a,c and triphenylphosphine were also investigated and compared to those for reaction with 1.For all three phosphines, the rate constants with 1d were slower than those obtained with 1 (k_H / k_D = 1.06 +/- 0.02).This result is in marked contrast with the results obtained with the deuterated phosphines.The results are consistent with a converted insertion of the phosphine into the peroxy bond of the dioxetane.