Polycyclic cage compounds

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],... 

The most widely exploited photochemical cycloadditions involve irradiation of dienes in which the two double bonds are fairly close and result in formation of polycyclic cage compounds. Some examples of alkene photocyclizations are given in Scheme 6.9. Entry 1 is a transannular cyclization. The preference for the observed product over tricyclo[4.2.0.02,5]octane does not seem to have been analyzed in detail. Entries 2, 3, and 4 involve photolysis in the presence of Cu03SCF3. Entries 5 and 6 are cases in which the double bonds are in close proximity and can cyclize to caged structures. 

Marchand, A.P. 1995. Polycyclic cage compounds Reagents, substrates and materials for the 21st century. Aldrichchimica Acta 28(4) 95-104. 

The most widely exploited photochemical cycloadditions involve irradiation of dienes in which the two double bonds are fairly close and result in formation of polycyclic cage compounds. Some examples are given in Scheme 6.7. Copper(I) triflate facilitates these intramolecular additions, as was the case for intermolecular reactions. 

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]. 

Intramolecular [2 + 2] photocycloadditions have been used successfully for the syntheses of (polycyclic) cage compounds. Recent examples of such reactions are the formation of pentacyclo[5.4.0.02 6.031°.05 9]undecane-8,ll-dione-4-spiro-l-cyclopentane,55 hexacy-clo[7.4.2.01,9.03,7.04 14.061s]pentadeca-10,12-diene-2,8-dione-5-spiro-l -cyclopropane,56 pen-tacyclo[5.4.0.02 6.031°.04 8]undecane57 and pentacyclo[6.4.0.02 7.03 12.06 9Jdodeca-4,10-diene.58 Irradiation of benzoquinone tetrahydropentalene adducts afford cage compounds which are easily converted to angular tetraquinanes.59... 

The polycyclic cage compounds of Group 14 elements heavier than carbon (i.e. tetrahedranes, cubanes, prismanes, etc.) have fascinated chemists for a long time because of their unique structures and expected unusual physico-chemical properties and reactivity1. It was quite reasonable to assume that such exotic compounds could possess properties... 

An interesting example of the synthesis of dihydropyrans using hetero Diels-Alder (HD A) methodology is the formation of the polycyclic cage compounds 3 from fulvenes and the tetracyclic enone 2 <06SL3479>. A HDA reaction also features in the synthesis of (+)-8-methoxygoniodiol <06TL4545>. 

The [HP(NR)3] anion (R = 2-methoxyphenyl) can be regarded as an imido analog of phosphite [HPOs] and is obtained by lithiation of the reaction product between phosphoms trichloride and 2-methoxyanilme. The lithium salt is in fact a polycyclic cage compound. ... 

Timmermans et al. report that diastereoselectivity can be induced in the intramoleuclar meta photocycloaddition of ethenes to the benzene ring as a result of minimisation of steric interactions between substituents on the linking tether of the bichromophore and a methoxy group at the 2-position of the arene unity this type of photoprocess has also been used as a key step in a formal synthesis of crinipellin B (Wender and Dore). New polycyclic cage compounds 43 have been obtained by irradiation of the [3.3,3] (1,3,5) cyclophane 44 (Sakamoto et al.) and Kubo et al. have described the intramolecular [3 + 2] photocycloaddition of bichromophores such as 45 which gives rise to nine- to eleven-membered ring systems 46. 

Geldenhuys WJ, Malan SF, Bloomquist JR, et al. Pharmacology and structure-activity relationships of bioactive polycyclic cage compounds a focus on pentacycloundecane derivatives. Med Res Rev 2005 25 21-48. 

Intramolecular [2 + 2] photocycloaddition of the quinone moiety of quinopimaric acid (48) to the isopropyl-substituted double bond leads to a polycyclic cage compound." 2-Hydroxynaphthoquinones undergo a formal [3 + 2] photocycloaddition with different cyclic alkenes, delivering chiral products (49). In the presence of a chiral template, a limited enan-tioselectivity is observed." ... 

Nair and coworkers [19] reported a hetero-Diels-Alder reaction of pentafulvene 36 (acting as a 2% component) with tetracyclic enone 70 (the 4jt-heterodiene), to give the polycyclic cage compound 71 containing a pyran moiety (Scheme 7.18). 

Prototypes of the photochemical reactions for the synthesis of cage compounds are classified as shown in Table 22.1. The most predominant examples are [2 + 2]-reactions of Diels-Alder adducts with an endo-configuration. Intramolecular photochemical [2 + 2]-, (6 +2 ]- and [6 -I- 6]-reactions in the rigid polycycHc framework have been increasingly employed for the synthesis of polycyclic cage compounds. Other photochemical reactions, such as [4 -t 4]-cycloaddition and related processes, are also important. According to this arrangement, prototypes of the photocycloadditions and their important applications are described. 

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