BH3 as a protecting group for phosphonic acid: a novel method for the synthesis of dinucleoside H-phosphonate

A BH3 group is found to be an effective protecting group for phosphonic acid esters. This new phosphonic acid protecting group was applied to the synthesis of a dithymidine H-phosphonate derivative from a dithymidine boranophosphate derivative. Triarylmethyl cations were found to be effective for the deprotection of the BH3 group in the dithymidine boranophosphate diester to afford the corresponding H-phosphonate derivative in excellent yield.