Ring‐opening reactions of 3‐substituted 1‐azabicyclo[1.1.0]butane with dichlorocarbene

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‐1,4‐diene (4a), which was characterized via conversion to the corresponding N‐substituted 5‐chloro‐1,2,3,4‐tetrazole, Sa. 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.