Isomers cages

Two more monometal fiillerene complexes are reported, Y Cg2 [105] and another La Cg2 isomer (La Cg2-B) [106]. A comparison of the electrochemical behavior under similar conditions is shown in Table 7.7 [105]. In general, similar electrochemistry is observed, but for both of these species, the second reduction wave is a two-electron process and no reductions occur at potentials similar to La Cg2-A s third reduction. The differences between the two La Cg2 isomers are attributed to either different Cg2 isomer cages or different positions of the La in the cage, with the former the most likely based on calculations [106,107]. No explanation of the nature of the two-electron reduction is given, as the previous explanation of an unoccupied orbital being filled is unlikely. 

In a recent total synthesis of the novel neurotrophic agent merrilactone A (22, Scheme 4) by Inoue and Hirama [24], key intermediate 21 with the cis-bicyclo[3.3.0] octane framework embedded within the caged pentacycle 22 was elaborated from cyclobutane 18 by a sequence of RCM and immediate cleavage of the resulting bicyclic vicinal diol 19 to raeso-diketone 20. Cyclooctenedione 20 then underwent regioselective transannular aldol reaction at low temperature (LHMDS, THF, -100 °C) to produce a 3 1 mixture of isomers in 85% combined yield. The major isomer 21 with the required stereochemistry was then converted into the racemic natural compound ( )-22 in 19 steps. 

This relationship has been found in spite of the fact that the spherical cage of Ceo has been severely distorted in the region of the defect which could have mitigated against correlations of this sort. This comment also applies to the CroMu isomers below. 

The detailed structures of several clathrates have been characterized, and a certain degree of selectivity on complexation with different isomers has been detected 21). Most of these complexes are of the channel type, but some of them have structures which simultaneously qualify for channel and cage type descriptors representative examples are illustrated in Figs. 19-21. The crystal data of the complexes are summarized in Table 1. 

The discovery of polyhedral boranes and polyhedral heteroboranes, which contain at least one atom other than in the cage, initiated a new era in boron chemistry.1-4 Most commonly, of the three commercially available isomeric dicarba-closo-dodecaborane carboranes(l,2-, 1,7-, and 1,12-), the 1,2-isomer 1 has been used for functionalization and connection to organic molecules. The highly delocalized three-dimensional cage bonding that characterizes these carboranes provides extensive thermal and kinetic stabilization as well as photochemical stability in the ultraviolet and visible regions. The unusual icosahedral geometry of these species provides precise directional control of all exopolyhedral bonds. 

Raman spectroscopy is a useful probe for detecting transannular S - S interactions in bicyclic or cage S-N molecules or ions. The strongly Raman active vibrations occur at frequencies in the range 180-300 cm-1, and for S- -S distances in the range 2.4-2.7 A. On the basis of symmetry considerations, the Raman spectrum of the mixed sulfur-selenium nitride S2Se2N4 was assigned to the 1,5- rather than the 1,3- isomer.37... 

The stepwise mechanism was also illustrated in terms of a temperature-dependent cage effect.23 Reaction of 24 with a mixture of lithium cyclo-hexyl-1-rf-oxide (48) and 3-pentyloxide (49) at 0°C, produced cross-over products 50 and 51, both in - and Z- forms, and the deuterium was scrambled in both isomers (89% in 50 and 6-12% in 51). In contrast, at —95—40°C, no... 

Fig. 6), which can be used as a bridgehead scaffold for the all-carbon cage molecule Q-C6o (42), an isomer of Ih-buckminsterfullerene that is 767 kcal-mol 1 higher in energy by the calculated heats of formation (RHF/3-21G).110,291 A similar macrocyde (45, C6oH6) of easier synthetic accessibility is based on the 1,3,5-triethynylbenzene moiety. 

Cleavage of the silsesquioxane octamer cage (c-C HnSilsO 513 with triflic acid produces a triflate intermediate that has been converted into the octasiloxanediol (r-C6H Si)70 o(OH)2 518, a constitutional isomer of 516 (Scheme 70).472 473... 

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