| Abstract
| - In the presence of catalytic amounts of tetraalkylphosphonium salts and under solventless conditions,primary aliphatic amines (RNH2: R = PhCH2, Ph(CH2)2,n-decyl, and 1-naphthylmethyl) are efficiently N-benzylatedto the corresponding RN(CH2Ph)2, using dibenzyl carbonateas the benzylating reagent. Compared to the reaction runwithout salt, where the competitive formation of the benzylcarbamate is favored, the phosphonium salt promotes highselectivity toward the benzylated amine and an increase ofthe reaction rate as well. However, in a single case exploredfor an amino acidic compound, namely 4-(aminomethyl)benzoic acid [4-(NH2CH2)C6H4CO2H], both N,N-dibenzylationand esterification of the acid group were observed. Analysisof the IR vibrational modes of benzylamine in the presenceof tetrabutylphosphonium bromide supports the hypothesisthat this enhanced selectivity may be due to an acid−baseinteraction between the salt and the amine, which increasesthe steric bulk of the amine and favors attack of thenucleophile on the less hindered alkyl terminus of dibenzylcarbonate.
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