Adamantene dimerization

Examination of models (Diagram 6) shows that, apart from a very skewed initial aay species, it seems impossible to have the triple afSy attachment of the product to the surface. Even the afi process cannot operate in the exchange of adamantane (see Section II). Rooney and his co-workers argue that loss of only 1H atom generating a surface alkyl may be sufficient to allow bond shift. This view is vindicated by the observation (59) that the very strained adamantene dimer (Diagram 7) isomerizes at rates comparable to those of exchange with... 

In an investigation of the contact reactions of highly strained cage compounds, Rooney and his co-workers (64,65) found that bicyclo(3,3,2)octane, protoadamantane, adamantene dimer, and other similar compounds were isomerized on platinum- and palladium-supported catalysts at relatively low temperatures (I50°-250°C on platinum, 2OO°-3OO°C on palladium). The ease... 

A v/c-dihaloadamantane undergoes the intermolecular reductive dimerization via unstable adamantene species to give stereoisomeric products in 80-90% yields, as in Eq. (34) [240]. Cathodic reduction of or, or -dibromo-l,2-dialkylbenzenes in the presence of dienophiles (maleic anhydride, etc.) and hinderd dienophiles provides diels-Alder adducts stereoselectively [241,242]. In this reaction, the dienophiles play a duel role as mediators... 

Evidence for the transient formation of adamantene in the dehalogenation of the dihalides (198 X = Br or I) and of homoadamantene in the Cope elimination of the iV-oxide [199 X = N(0)Me2] and the Hoffmann elimination of the quaternary ammonium hydroxide (199 X = NMe3 0H") has been adduced from the isolation of cyclobutane-type dimers of these highly strained olefins. The present state of knowledge of Bredt s rule and bridgehead olefins has been reviewed by Buchanan. ... 

At last adamantene has probably been prepared. In similar studies, 1,2-di-iodoadamantane and l-bromo-2-iodoadamantane have been used as precursors (Schemes 26 and 27). The evidence for formation of the adamantene rests in the isolation of the CjoHjb hydrocarbons, formally dimers of adamantene. The stereochemistry of the adducts is unknown and adamantene could not be trapped in attempted preparation of adducts with suitable dienophiles. 

---