Bridgehead functions

The product [2]15b represents the best entry to doubly bridgehead functionalized [2]staffanes at the moment. 

The chemistry of centrotetraindane 8 has not been explored in detail. It may be noted, however, that the rigidity of the tribenzotriquinacene backbone renders the framework of 8 also conformationally rigid, giving rise to a single, Cs-symmetric conformer, as confirmed by X-ray structure analysis [114]. Bridgehead-functionalized derivatives of 8 should provide a wealth of further carbon-rich polycyclic compounds. 

Bridgehead functionalization. A method for introducing an iodine atom at a bridgehead adjacent to a ketone is by oxidation of the derived acetal such as (1) with Phl(OAc)j-l2. 

Lead tetraacetate trifluoroacetic acid Bridgehead functionalization Formamides s, 31,123... 

Bridgehead functionalization. C1O3 added in small portions with cooling below 35° during 1 hr. to a soln. of bicyclo[3.3.1]nonane in acetic acid-acetic anhydride, and stirred 6 hrs. at room temp. l-bicyclo[3.3.1]nonanol. Y 40-50%. F. e. s. R. C. Bingham and P. v. R. Schleyer, J. Org. Chem. 36, 1198 (1971). 

Setaka W, Hamada N, Kira M (2004) Novel synthesis and bridgehead functionalization of permethylbicyclo[2.2.2]octasilane. Chem Lett 33 626... 

In accordance with the electropositive nature of the bridgehead atoms, all di(pyridyl) substituted anions behave like amides with the electron density accumulated at the ring nitrogen atoms rather than carbanions, phosphides or arsenides. The divalent bridging atoms (N, P, As) in the related complexes should in principle be able to coordinate either one or even two further Lewis acidic metals to form heterobimetallic derivatives. According to the mesomeric structures, (Scheme 7), it can act as a 2e- or even a 4e-donor. However, theoretical calculations, supported by experiments, have shown that while in the amides (E = N) the amido nitrogen does function as... 

Certain nucleophilic substitution reactions that normally involve carbocations can take place at norbomyl bridgeheads (though it is not certain that carbocations are actually involved in all cases) if the leaving group used is of the type that cannot function as a nucleophile (and thus come back) once it has gone, for example. 

The utility of lOOC reactions in the synthesis of fused rings containing a bridgehead N atom such as pyrrolizidines, indolizidines, and quinolizidines which occur widely in a number of alkaloids has been demonstrated [64]. Substrates 242 a-d, that possess properly positioned aldoxime and alkene functions, were prepared from proline or pipecolinic acid 240 (Eq. 27). Esterification of 240 and introduction of unsaturation on N by AT-alkylation produced 241 which was followed by conversion of the carbethoxy function to an aldoxime 242. lOOC reaction of 242 led to stereoselective formation of various tricyclic systems 243. This versatile method thus allows attachment of various unsaturated side chains that can serve for generation of functionalized five- or six-membered (possibly even larger) rings. 

The infrared (IR) spectra of these compounds were mostly studied in the solid state which showed all the basic peaks characteristic of various functionalities attached to such bicyclic heterocycles with bridgehead nitrogen atoms. The difference in the frequency of carbonyl and carbon nitrogen double bond in tautomers of compound 18 (R = H) has been discussed previously in CHEC-II(1996) <1996CHEC-II(8)713>. 

In another example (Scheme 8), the intramolecular cycloaddition of an azido functionality onto an enone group afforded bicyclic derivatives with bridgehead iV atoms. The cyclopentenone derivative 28 afforded the indolizidinone 30 through the proposed compound 29 which might react through a diradical intermediate or through a betaine intermediate <2002TL5385>. 

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