PALLADIUM-MEDIATED SYNTHESIS OF URETHANES FROM AMINES, CARBON-DIOXIDE, AND CYCLIC DIOLEFINS

Addition of preformed carbamate anions RR'NHCO2-+HBase, generated from various primary and secondary amines and carbon dioxide, to (norbornadiene)palladium dichloride at -78-degrees-C followed by addition of DIPHOS (bis(diphenylphosphino)ethane) and then reductive cleavage at 0-degrees-C with sodium borohydride gave nortricyclo carbamate esters (1a-d) in good yields (75-100% by GC). Cleavage with anhydrous hydrogen chloride also gave nortricyclo carbamate esters. Addition of (dicyclopentadiene)palladium dichloride to the carbamate anion at 0-degrees-C gave the corresponding carbamate esters (2a-i) in good yields (53-100% by GC) after reductive cleavage with either sodium borohydride or dihydrogen. Addition of BuNHCO2-+H3NBu to 1,4-(cyclooctadiene)palladium dichloride at -35-degrees-C followed by reductive cleavage with sodium borohydride gave cyclooct-4-enyl-1 N-butylcarbamate (3) in 16% isolated yield. An indication of the nucleophilicity of the carbamate anion was obtained by direct competition studies with the acetate anion on attack on (dicyclopentadiene)palladium dichloride at 0-degrees-C. The relative rate of reaction of BuNHCO2-+H3NBu vs AcO-+H3NBu was determined to be 1:2.66.