The Addition of Halocarbenes to Bridged Bicyclic Olefins

Abstract

It is well known that halocarbenes add stereospecifically to olefins to yield halocyclopropanes which undergo, in appropriate cases, rearrangement to allylic halides. When a bridged bicyclic olefin, such as norbornene is used, these reactions take on new dimensions from the mechanistic and synthetic point of view. The rigid geometry and symmetry of the olefin enable significant information to be obtained on both the nature of the addition and the subsequent rearrangement processes. The behavior of monohalo- and dihalocarbenes (e.g. CHX and CX₂ where X = Cl, Br and F; and CXY where X = F and Y = Cl, Br) has been investigated with respect to substituted norbornenes, bicyclo[2.2.2]octene-2 and bicyclo[3.2.1]octene-2.
The role of attractive and repulsive forces on the orientation of the carbene addition to the double bond is discussed. The rearrangement process, which is uniquely controlled by the geometric constraint imposed on the cyclopropane adduct and by the configuration of its substituents, is most completely described by the Dewar-Zimmerman rules.
The addition of halocarbenes to such freely available bridged bicyclic olefins permits convenient synthesis of their less accessible higher homologues.