Trimethylsilyl azide adds smoothly to the highly strained N-C(3) σ-bond in 3-ethyl-1-azabicyclo[1.1.0]-butane (1) to afford an adduct, 2, that reacts in situ with a variety of electrophilic reagents (i.e., ethyl chloroformate, p-toluenesulfonyl chloride, benzoyl chloride, acetyl chloride, and oxalyl chloride) to afford the corresponding N-substituted-3-azido-3-ethylazetidines 3-7, respectively in 62-72% yield. Similarly, 1 reacts regiospecifically with "mixed anhydrides" (i.e., p-toluenesulfonyl acetate, methanesulfonyl acetate, and benzoyl trifluoromethanesulfonate) to afford the corresponding adducts, 8-10, respectively) in 38-68% yield. Reaction of p-toluenesulfonyl azide with 1-aza-3-phenylbicyclo[1.1.0]butane (12) produces two products: N-(p-toluenesulfonyl-3-azido-3-phenylazetidine (13, 15%) and a dimeric product, N-(N′-p-toluenesulfonyl-3′-phenyl-3′-azetidinyl)-3-azido-3- phenylazetidine (14, 28%). Ethyl chloroformate adds to the N-C(3) σ-bond in 1-aza-3-(bromomethyl)bicyclo[1.1.0]butane (15) to afford N-carboethoxy-3-(bromomethyl)-3-chloroazetidine (16) in 73% yield.