Synthetic and mechanistic aspects of halo-F-methylphosphonates

The synthesis of a variety of new halo-F-methylphosphonates has been achieved by a Michaelis-Arbuzov type reaction between a halo-F-methane and a trialkyl phosphite. This synthesis has proved to be of wide scope and utility for the high yield preparation of a number of heretofore unknown compounds. The H-1, F-19, C-13 and P-31 NMR spectroscopic properties are reported in detail. The mechanism for the formation of bromodifluoromethylphosphonates has been shown to proceed through the intermediacy of difluorocarbene:CF2. The phosphonate products have been shown to react with a wide variety of reagents. Fluoride and alkoxide ions react by attack at phosphorus with cleavage of the carbon-phosphorus bond and formation of [:CF2] from the bromodifluoromethylphosphonates and the CFBr2- anion from the dibromofluoromethylphosphonates. Iodide ion and tertiary phosphines react by attack at the ester carbon to give stable phosphonate salts. Hydrolysis of the phosphonate esters with 50% aqueous HCl gives the expected phosphonic acids. Trimethylsilyl bromide attacks phosphoryl oxygen to afford the bis(trimethylsilyl) esters. (C) 2011 Elsevier B.V. All rights reserved.