NMR Studies of the Hydration Equilibria of Mesylate and Dialkyl Phosphate Derivatives of Acetone; and Investigations of Novel Hypervalent Iodine Compounds

The aryl-λ³-iodane, [hydroxy((bis(2,2,2-trifluoroethoxy)phosphoryl)oxy)iodo]benzene (1), was prepared from [hydroxy(tosyloxy)iodo]benzene and sodium bis(trifluoroethyl) phosphate in methanol. This novel iodine (III)-phosphate reagent was employed for the conversion of acetone to its α-bis(trifluoroethyl) phosphate derivative, and for ligand-transfer oxidations of various alkyl iodides to the corresponding alkyl bis(trifluoroethyl) phosphates.

The use of 1 for oxidative rearrangements of arylalkenes to geminal-bisphosphate esters was also explored. Samples of 1 and the known diphenyl analogue, [hydroxy((bis(phenyloxy)phosphoryl)oxy)iodo]benzene were submitted for single crystal X-ray analysis.

Equilibrium constants (K_D) for the hydration of α-(mesyloxy)acetone, α-((bis(methoxy)phosphoryl)oxy)acetone, and α-((bis(ethoxy)phosphoryl)oxy)acetone in D₂O at 25, 35, 45, and 55 °C were determined by 1H NMR analysis. Plots of log K_D versus T-1 enabled calculations of the enthalpy (H) and entropy (S) of hydration for all three substrates. Hydration constants of the ketol phosphates in D₂O (K_D) and H₂O (K_H) at 25 °C were also determined by ³¹P NMR analysis. The hydration constants were employed with reported linear free energy relationships for estimates of Taft polar substituent constants (σ^*) of the (mesyloxy)methyl and bis((alkoxy)phosphoryl)oxy)-methyl groups, and equilibrium constants for hydroxide addition to the ketol phosphates. Hydration of the α-bis(trifluoroethyl) phosphate derivative of acetone in D₂O was accompanied by spontaneous hydrolysis of the ketol phosphate to two sets of products. The mechanistic origin of the phosphate products was examined by conducting the hydrolysis in D₂O mixed with ¹⁸O-labeled H₂O.

4,4-Dimethyl-2-nitromethyl-2-(diacetoxyiodo)biphenyl was synthesized from 4,4-dimethyl-2-iodobiphenyl and submitted for single crystal X-ray analysis. A key step in the synthetic procedure was ring-opening of a cyclic iodonium salt with nitromethane anion. A preliminary ¹H NMR study of the dynamic behavior of the biaryl-3-iodane was conducted and its cyclization with p-toluenesulfonic acid to a dibenziodonium salt was demonstrated. Efforts to convert the diacetoxyiodane and the corresponding iodo compound to an iodine (III) heterocycle containing the 9-iodaphenanthrene ring system were unsuccessful.