Bredt alkenes

Strained n/d/ -Bredt alkenes as well as -cycloalkenes will undergo [2 + 2] cycloadditions with alkenes. The bridgehead bicyclo[3.3.1]nonenones 16, produced as a transient species by the dehydrobromination of the corresponding bridgehead bromoketone, undergo cycloaddition with 1,1-dimethoxyethenc (15) to give the tricyclic ketones 17 in quantitative yields.7... 

The feasibility of intramolecular type II annulations between furans and vinylcarbenoids to give highly strained molecular frameworks that contained a -Bredt alkenes is depicted in Equation (13) <1997TL1737>. 

Anti-Bredt alkene a polycyclic alkene that contravenes Bredt s rules by having a C=C bond attached to a bridgehead carbon atom... 

However, in other instances, postelimination reactions can change the nature of the products. The main difficulty arises from the readdition of the alkene initially produced to the hydrido complex. This can result in isotopic scrambling or isomerization of the alkene upon reelimination. The formation of internal alkene products from the [Pd(PPh3)4]-catalyzed decarbonylation of acyl cyanides (equation 2) may also arise from postelimination reactions between the alkene and [PdH(CN)(CO)(PPh3) ] initially formed. The importance of this reaction in isomerizing the anti-Bredt alkenes formed by the catalytic decarbonylation of 3-chlorocarbonyltricyclo[5.3.1.0 ]iindecane is shown in Scheme 3. 

Debromination of 1,2-dibromoalkanes. Bis(trimethylsilyl)niercury de-brominates 1,2-dibromoalkanes to olefins. This reaction has been applied to 1,2-dibromo- and 1,2-diiodoadamantane (2) as a route to adamantene (a). When performed in the presence of 1,3-diphenylisobenzofuran, the hydrocarbon 3 is obtained in 30-35% yield. In principle, this route could be extended to isolation of adducts of other anti-Bredt alkenes. 

Anti-Bredt alkenes, 56, 137, 217 Antimony(V) fluoride, 20-21 Aphidicolin, 205, 206, 294 Aplysistatin, 512 Apotphines, 201, 513-514 Arachidonic acid, 242-243 a-Arenechromium tricarbonyl complexes, 21, 117-118... 

Isomerization ofanti-Bredt alkenes The reagent 1 forms a complex with 2 that is stable for some months at -20°, but that rearranges at 60° largely to a mixture of 2, 3, and 4, in the ratio 2 10 2 with a trace of 5. 

Careful deuterium exchange and mass spectral studies have also shown that proton abstraction in other carbons proximal—but not vicinal—to a ketone is also possible. The intermediacy of rather odd species like VII, which feature some of the strain character found in anti-Bredt alkenes and VIII, which nec-... 

Whereas a trimethyl 1-methylene-2,4,5,6,7,7a-hexahydroindene-3,5,5-tricarboxylate 30 is the sole product of the palladium(0)-catalyzed reaction, the nickel(0)-catalyzed reaction, although proceeding only with low turnover numbers, produces the anti-Bredt alkene, trimethyl 9-methylenebicyclo[4.2.1]non-8-ene-3,3,8-tricarboxylate29, selectively. Neither an addition of excess cyeloocta-1,5-diene nor a stoichiometrie amount of nickel(O) with respeet to the substrate allowed for an improvement of the yield. ... 

Results of a study of the generation and reactivity of 2-R-substituted adamantanes (bridgehead anti-Bredt alkenes) suggest that they may have a biradical nature, and that the R suppresses the dimerization rate. ... 

---