Addition of trimethylsilyl azide and of “mixed anhydrides” to the N‐C(3) σ‐bond in 3‐substituted‐1‐azabicyclo[1.1.0]butanes

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.