Cage compounds, synthesis

There is another type of multiple thermal Diels Alder reaction in which the initial monoadduct is involved, either directly or after one transformation, in a second cycloaddition that affords the final polycyclic compounds. These methodologies have been used especially in the synthesis of polycyclic cage compounds. Paquette was the first to report the conversion of 9,10-dihydroful-valene into polyfused cyclopentanoid systems [124],... 

However, the classical version of the ABAC, when triallyl-, trimethallyl-, or tricrotylborane are involved in the reaction with RR1CHC=CH (e.g., propargylic ethers), can be applied only for the synthesis of 1-boraadamantane derivatives 35, 3,5-dimethyl- 36 and 4,6-dimethyl-l-boraadamantanes 37 (Scheme 7). Hence, the stmctures of the final cage compounds are rigidly restricted by the stmctures of the starting allylic boranes. 

Intramolecular (2 + 2)-photocycloaddition has proved to be an excellent route to the synthesis of the so-called cage compounds. Ideally, this route utilizes substrates where the two alkene moieties are held face-to-face within a pre-formed structure. The irradiation brings about excitation and coupling of the two groups to afford a cyclobutane ring. 

Example 28 a caged compound includes a photocleavable-protecting group that masks an essential functionality upon removal by photolysis [58]. Imperiali and associates have developed an interassembly approach for the synthesis of peptides containing l-(2-nitrophenyl)ethyl-caged phos-phamino acids [59]. The peptides described in that paper are based on phosphorylation sites of kinases involved in cell movements. 

Proceeding from a precursor polyaza-caged structure, which may be different from the desired product, but includes the final structure within the cage. Although not a caged compound the synthesis of RDX from the nitrolysis of hexamine would fit this category. 

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]. 

Photocyclodimerizations have also been applied to the synthesis of cage compounds.47 Thus, acetone sensitized irradiation of pentacyclo[6.6.0.02 12.03 6.07-11]tetradeca-4,9,13-triene (24) affords heptacyclo[6.6.0.02 7.03,6.04,14.05 9.010,13]tetradec-l l-ene (25)48 and direct irradiation of l,4,5,8-tetrahydronaphthalene-2,3-dicarboxylic anhydride in dioxane yields four isomeric double tetraasteranes (nonacyclo[10.8.0.02 11.04,9.04 19.06-17.07,1< 0914.014 19]eicosan).49... 

The first section will consist of the synthesis and reactions of imine chelates, as this is the most widely and consistently used aspect of ligand reactions. The discussion will be subdivided according to the types of ligands involved and will range from bidentate through to multidentate ligands, macrocycles and cage compounds. 

The hollow interior of dodecahedrane and other organic cage compounds described in section 4.9 is much too small to envelop atoms, ions, or molecules. Tight closed-shell macromolecules have been obtained from vesicles by several research groups, by polymerization of amphiphiles possessing double or triple bonds within the membrane or at the head groups. Smaller, but well-defined, closed-shell containers have been obtained by two other methods described below, namely by directed synthesis and by formation of closed-shell all-carbon molecules in graphite vapor. 

The facially perturbed enantiopure (.S, .S )-2-(p-tolylsulfinyl)norborncno-/7-bcnzoquin-ones (119), undergo asymmetric Diels-Alder additions with cyclopentadiene to yield the four possible adducts (120) and (121). The endo-syn cycloadducts (121) can be used in the synthesis of the cage compound garudane (122) (Scheme 44).234 The antiaromatic compound 1,4-biphenylenequinone (123) has been synthesized and trapped by Diels-Alder reaction with cyclopentadiene (Scheme 45).235 The 4 + 2-cycloadditions of 4-methylene-5-(bromomethylene)-4,5-dihydrothiazole with 2- and 3-bromonaphtha-quinones are highly regiospecific.236... 

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... 

Octasilacubanes seem to be the most widely studied cage compounds, several examples of their reactivity having been described. To date, five examples of the octasilacubanes have been reported in the literatureld 2,31-36. Their synthesis, as well as structural parameters and reactivity, were summarized in a recent reviewld. 

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... 

Scheme 24. The molecular LEGO set used for the synthesis [142] of the molecular cage compound — trinacrene 85...

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