[Synthesis of a strain molecule, 1-azabicyclo [1.1.0] butane].

1-Azabicyclo [1.1.0] butane (ABB) bearing the highly strained bicyclic structure, which is synthetically useful for the preparation of 3-substituted azetidines, was obtained by the cyclization of 2,3-dibromopropylamine hydrobromide derived from inexpensive allylamine only with organolithium compounds and lithium amides. When other bases were employed, such as potassium, sodium, and magnesium species, the reaction yielded almost no ABB. It was speculated that a lithium cation played an important role in the cyclization. Thus, we proposed that this reaction proceeded by the consecutive cyclization to aziridines via the SN2 process involving the activation of the C-Br bond based on the intermolecular Br…Li(+) coordination, as a result of studies of reaction mechanisms.