Adamantylfuroylphosphonates: Synthesis and Further Transformations

Methods for the synthesis of 5-(adamantan-1-yl)furan-2- and -3-carboxylic acids were developed. Phosphorylation of the acid chlorides of these acids with triethyl phosphite yielded stable furoylphosphonates, which then reacted with ethoxycarbonylmethylenetriphenylphosphorane to form 3-[(5-adamantan-1-yl)furanyl]-3-(diethoxyphosphoryl)acrylates. Bromination of the methyl group of these compounds with N-bromosuccinimide provided bromomethyl and dibromomethyl derivatives. The latter were converted under mild conditions to the corresponding aldehydes, which in turn reacted with hydrazine to give adamantylated derivatives of dihydrofuro[2,3-d][1,2]diazepine. Further treatment of bromomethyl derivative with thiourea and subsequent hydrolysis of the resulting thiouronium salt led to the formation of 4,7-dihydro-5H-thiopyrano[3,4-b]furan containing an adamantyl moiety.