Synthesis of N-Boc-3-pyrroline

tert-Butyl 2,5-dihydro-1H-pyrrole-1-carboxylate (N-Boc-3-pyrroline) is a useful intermediate for preparing substituted pyrrolidines. It is obtained by ring-closing metathesis of N-Boc-diallylamine, prepared from diallylamine and di-tert-butyl dicarbonate.

A very small amount of the first-generation Grubbs catalyst in refluxing dichloromethane is enough. The ethylene released drives the equilibrium, and the carbamate prevents the basic amine nitrogen from coordinating to ruthenium and deactivating the catalyst.