A Novel Synthesis of 1,4,7,10-Tetraazacyclododecane by the Tandem Reaction of a Vinylsulfonium Salt

1,4,7,10-Tetraazacyclododecane was synthesized through 4 steps by using easily available diphenylsulfonium triflate as a key annulation reagent. The reaction condition was very mild and the yield was high. After oxidation and hydrolysis, 1,4,7,10-Tetraazacyclododecane, which had been proven to be the pivotal precursor for a wide range of MRI contrast reagents, was produced in an overall yield of 31%.