Caged ring systems

Unsubstituted alkyl diazirines are ruled out because carbenes from them rearrange to olefins (Fig. 3.14). The constraints of the caged ring system do not allow this possibility with the useful adamantane diazirine, although here a fraction of the carbene is lost by intramolecular insertion (Fig. 3.15). 

Rokach, J., Girard, Y., and Atkinson, J.G., A new heterocyclic cage ring system preparation of the cis-cyclobutane dimer of dibenz[a,d]cyclohepten-5-one,7. Chem. Soc., Chem. Commun., 602,1975. 

SCHEME 20 A new heterocyclic cage ring system the preparation of the c/s-cyclobutane dimer of benzo[a,d]cyclo-hepten-5-one. 

In compound 91 the diborahexasiloxane ring system 89 can be identified, which has been expanded to a three-dimensional structure by an additional (R2Si0)20 fragment bridging now, in contrast to compound 90, two boron atoms [127], This cage can be obtained in yields of 45% from tetraphenyldisiloxanediol and boric acid when reacted in a 6 1 stoichiometry. The molecule contains a... 

The P—N skeletal features of the cyclophosph(III)azanes and related cage compounds discussed here are summarised in Fig. 11. This shows that considerable advances have been made since 1960 when only one cyclophosph lII)azane ring system... 

It is necessary to differentiate between reactions where the two identical moieties undergoing photocyclodimerization, i.e. the chromophores, are part of the same molecule (such reactions are formally photoisomerizations with coincident ring formation) on the one hand and intermolecular photocyclodimerizations on the other. The former reactions, which will be treated first, can occur in molecules where the two (identical) moieties are linked together by a simple chain (to afford polycyclic systems), or by a ring system (to afford cage compounds). 

The benzyne functions as a dienophile towards reactive diene systems. The reactivity of the 9,10-positions in anthracene is well known (Diels-Alder reaction, Section 7.6), and addition of benzyne to 9-bromoanthracene yields the interesting cage-ring alkyl halide 9-bromotriptycene (9-bromo-9,10-o-benzenoanthracene). The reaction is incomplete and some unreacted 9-bromoanthracene remains in the crude reaction products, but may be removed by virtue of its ready conversion into a maleic anhydride adduct in a further Diels-Alder-type reaction. 

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