Synthesis of functionalized alkoxyalkylidene gem-bisphosphonates

We report the synthesis of a series of new functionalized bisphosphonates and bisphosphonic acids with an alkoxy group fixed at the geminal carbon, which is proposed to increase their lipophilicity and so their bioavailability. Subsequently, the alkylation of these alkoxy bisphosphonates with allyl bromide is reported. The reactivity of the allyl group has been studied to give access to alkoxy bisphosphonates functionalized by diverse groups including alcohol, aldehyde, carboxylic acid, epoxide and amine.