Highly selective carbamation of aliphatic diamines under mild conditions using Sc(OTf)3 as catalyst and dimethyl carbonate as a phosgene substitute

Sc(OTf)3 is an effective catalyst for bis-carbomethoxylation of aliphatic diamines with dimethyl carbonate (DMC) under very mild conditions. At ambient temperature (293 K), in the presence of Sc(OTf)3, aliphatic diamines, such as 1,6-diaminohexane (1), 1,4-diaminobutane (2), 1,3-diaminopropane (3), meta-xylylenediamine (4) and para-xylylenediamine (5), react with DMC to afford the corresponding di-carbamates in high yields. The carbomethoxylation reaction is highly selective (≈100%). Under the used working conditions, side-reactions, such as formation of ureas and/or N-methyl derivatives, are repressed. The starting catalyst, Sc(OTf)3, modifies during the catalytic process and converts into Sc-methoxo species by losing OTf groups, as the isolation of unprecedented mono-urethane triflic salts, (MeO(O)CNH–R–NH3)O3SCF3 (R = –(CH2)6–, meta-C6H4(CH2)2–), also indicates. The modified catalyst can be recovered at the end of the reaction and recycled.