Cage compounds strain

Considerable current interest and sustained research efforts of some groups in the USA and other countries have been aimed at the synthesis and chemistry of strained energetic compounds. According to Marchand and co-workers, polynitro polycyclic cage compounds are important members of this class [110]. 

Recently, some attention has been focused on the synthesis and on the properties of strained cage compounds made up exclusively of Si atoms. As a consequence a number of derivatives of tetrasilatetrahedrane, hexasilaprismane and octasilacubane have been synthesized. The current knowledge in the field up to 1994 has been summarized... 

The behavior of stilbene radical cations in the semiconductor catalysis is in keeping with the result of photoisomerization of other olefins like 6-methylstyrene sensitized by electron acceptors like chloranil in polar solvents (48). The semiconductor photocata-lyzed isomerization of strained cyclobutanes to strained dienes (isomerization of quadricyclene to norbomadiene and similar reactions of complex cage compounds (49)) is related to the olefin isomerization discussed above. 

Instances of an R Ge—P bond are confined to one example, the ada-mantane-like cage compound, [(CH3)3Ge]6P4 (51). The Ge—P distance (2.3217 A) is equal to the sum of covalent radii (2.32 A), although the strained trifurcated bonding of each phosphorus atom (Fig. 10) suggests that this may not be representative of a typical covalent Ge—P bond. Such speculation awaits further study for confirmation. 

TABLE 24. Strain energies (kcalmol ) in M H cage compounds"... 

Cyclisation of 139 is not regioselective and gives a 60 40 mixture of six- and five-membered rings, but the same class of reaction starting from 140 allows the synthesis of the remarkable strained cage compound 141.69... 

Highly strained cage compounds can also be prepared by the same method of simple cyclopropanation with diazomethane in the presence of palladium(II) acetate. This was applied to the fourfold bridged tricyclic heptacyclo[10.8.0.0 . 0 .0 . 0 .0 ]eicosa-l(12)16-diene (6), which reacted with diazomethane in the presence of catalytic amounts of palladium(II) acetate to afford a mixture of mono- and bis-adducts 7 and 8 in 68 and 3% yield, respectively. These were separated by column chromatography on silica gel. The monoene 7 was converted into the bis-adduct 8 by repeating the same cyclopropanation reaction. ... 

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... 

Highly strained cage compounds have long attracted considerable attention from both experimentalists and theoreticians.724 The most important structural component of cage compounds is very often a highly strained cyclobutane ring, which is easily accessible by a photochemical route.725 Cubane for its aesthetic beauty counts as one of the milestones in synthetic (photo)chemistry and structural organic chemistry.726 A... 

Strained cage compounds can be made by intramolecular photocycloaddition of properly designed ene/enone substrates. In an interesting example from J. R. Scheffer, a ben-zoquinone derived Diels-Alder product is regioselectively transformed into a (halO cage compound. This is a more complicated version of the classical intramolecular photochemical cyclization reactions of benzoquinone derivatives (for example see B. Pandey s cage synthesis from a naphthoquinone-cyclopentadiene in Chapter 3). 

The photochemical reversion of the cage compound (274) into the diene (275) has been studied by Mukai and his co-workers.The process can be brought about by various catalysts such as ZnO or CdS. These experiments are related to the utilization of strained cage compounds as a means of energy storing. Mukai et have further reported on their detailed study of the cycloreversion reactions of cage compounds (276) involving electron-transfer processes. Another report has described work with cationic sensitizers (277). ° ... 

The structure of the unusual caged hydrocarbon Binor-S has been established by an analysis of the dione derivative (88), The valence angles in the nortricyclanone subunits indicate considerable strain [e.g. C(l)-C(7)-C(4) 101.3°], and the six- and eight-membered rings are both in boat conformations. The reaction of ethylenediamine and glyoxal has been shown to produce the heterocyclic cage compound (89) " in which the two... 

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