The Reaction of Dihalocarbenes with Quadricyclane

The reactions of difluoro‐, dichloro‐ and dibromocarbene with quadricyclane ( 2 ) were examined. In all cases, conversions were low (4–15%), but three distinct reaction courses were observed: cleavage, 1,2‐addition, and 1,4‐addition. Difluorocarbene gave mainly 6‐ endo ‐(2,2‐difluorovinyl)‐ cis ‐bicyclo[3.1.0]hex‐2‐ene ( 8 ; 52–89% relative yield), together with minor amounts of exo ‐3,3‐difluorotricyclo[3.2.1.0 2,4 ]oct‐6‐ene (7; 13–17%), and 4,4‐difluorotetracyclo[3.3.0.0 2,8 .0 3,6 ]octane ( 5 ; 2–4%). Dichlorocarbene gave analogous products, but in relative yields of 35 ( 17 ), 51 ( 11 ), and 12% ( 16 ). The product 11 of 1,2‐ endo addition underwent further rearrangement to its allylic derivative 12 . A small amount of 1,2‐ endo addition also occurred (2% of 14 / 15 ). Dibromocarbene gave predominantly products derived from rearrangement of the 1,2‐ exo (61% of 20 / 21 ) and 1,2‐ endo adducts (10% of 23 / 24 ). In addition, a significant amount of 4,4‐dibromotetracyclo[3.3.0.0 2,8 .0 3,6 ]octane ( 25 ; 21%) was formed. The cleavage product, 6‐ endo ‐(2,2‐dibromovinyl)‐ cis ‐bicyclo[3.1.0]hex‐2‐ene ( 26 ) was also observed (7%). The yields and product compositions were compared to those obtained from norbornadiene ( 1 ) and found to be entirely different ( Table 1 ), for example no cleavage occurred with difluorocarbene.