Synthesis of Bridged Bicyclic Molecules using Halocarbenes. Derivatives of bicyclo[4.2.1]nonane

The addition of dichlorocarbene (generated by the interaction of sodium methoxide and ethyl trichloroacetate) to bicyclo[3.2.1]oct‐2‐ene, its 3‐chloro and exo ‐3,4‐dichloro derivatives gives the exo 1 : 1 adducts in yields of 94, 89 and 48%. By suitable chemical reactions of these adducts, convenient syntheses of bicyclo[4.2.1]nona‐2,4‐diene and bicyclo[4.2.1]non‐3‐ene, together with their monochloro, dichloro and trichloro derivatives are obtained. Bicyclo[4.2.1]‐nonan‐3‐one is also obtained from bicyclo[4.2.1]non‐3‐ene in a synthesis starting from the readily available 5‐hydroxymethylnorborn‐2‐ene in an overall yield of 20%.