Synthesis of 2,5- and 2,6-bis(bromomethyl)-1,4-diphenylpiperazines and their conversion into 2,5-diphenyl-2,5-diazabicyclo[2.2.2]octane
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Treatment of cis-1,5-diphenyl-3,7-dihydroxyoctahydro-1,5-diazocine (1) with phosphorus tribromide yielded a mixture of cis-2,6-bis(bromomethyl)-1,4-diphenylpiperazine (4) and cis-2,5-bis(bromomethyl)-1,4-diphenylpiperazine ( 5 ). The structures of 4 and 5 were confirmed by conversion to the corresponding dimethyl-1,4- diphanylpiperazines (6 and 7) by lithium aluminum hydride. Compounds 6 and 7 were synthesized from cis-2,6- and cis-2,6-dimethylpiperazines. Both 4 and 5 on treatment with magnesium in tetrahydrofuran were converted to 2,5-diphenyl-2,5-diazabicyclo[2.2.2]octane (8). The interconversion of 4 and 5 is discussed.