Reaction of 3-ethyl-1-azabicyclo[1.1.0]butane (1a) with chloroform-potassium tert-butoxide afforded a ring-opened product, 1,1-dichloro-2-aza-4-ethylpenta-l,4-diene (4a), which was characterized via conversion to the corresponding N-substituted 5-chloro-1,2,3,4-tetrazole, 5a. Reaction of 3-phenyl-1-azabicyclo[1.1.0]butane (1b) with "Seyferth's reagent" (PhHgCCl2Br) afforded 1,1-dichloro-2-aza-4-phenylpenta-1,4-diene (4b), which also was characterized via conversion to a tetrazole derivative, i.e., 5b. Finally, the reaction of 1b with dichlorocarbene generated under phase transfer conditions (chloroform-sodium hydroxide-TEBA) was studied. At short reaction times (0.5 hour), the major reaction product was 4b. However, at longer reaction times (20-30 hours), two secondary products, 8 and 9, were formed which resulted via subsequent dichlorocyclopropanation of 4b.