Diels-Alder adducts cage compounds

The cage compound (301) is formed efficiently on irradiation of the adduct (302).Irradiation of the ene dione (303) affords the cage compound (304) by a (6 + 2)-cycloaddition. The Diels-Alder adducts (305) are photochemically reactive. Irradiation of (305) affords either the cage compounds (306) by a (2+2)-cycloaddition reaction, a process favoured by the adducts (305 a,b), or the oxetanes (307). The structures (306, 307) were verified by 2L ray diffraction studies The quinone adduct (308) also undergoes photochemical cyclization to afford the cage diketone (309). This material was subjected to flash vacuum pyrolysis to yield the diketone (310) important in the synthesis of perhydroindacenes. ... 

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. 

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... 

Substituted phosphorus heterocycles of varying degrees of unsaturation were easily obtained via Diels-Alder reaction and such adducts may be further aromatized or functionalized to provide phosphorus containing cage compounds < 1996PS(109)425, 1999S644, 1999EJ0363>. 

Reaction of cycloheptatriene with p-benzoquinone in toluene at 110°C gave the [4 + 2] adducts (282), the uic-ditropyl product (283), a small quantity of 7,7 -bitropyl, and hydroquinone. " More complex behaviour was observed for the reaction conducted in the absence of solvent in addition to the above compounds, the wic-ditropyl derivative (284) and the cage compound (285), formed by intramolecular Diels-Alder reaction of (283), were also isolated, all in very low yield. The formation of (283) appears to involve a biradical process. ... 

Cookson et al. first reported prior to 1965 that photochemical reaction of the Diels-Alder endo-adducts of cyclopentadiene or cyclohexa-1,3-diene with p-benzoquinone gave cage compounds by formation of a cyclobutane ring from the two double bonds. Irradiation of an ethyl acetate solution of the cyclopentadiene adduct 36 with a medium pressure Hg lamp for 6 h afforded cage 37 (90%). This photoreaction proceeded even in the soHd state, and the cage compound 37 was obtained in 80% yield after 80 h irradiation. Similarly, the 1 1 adduct 38 of cyclohexa-l,3-diene and p-benzoquinone was converted into cage 39 by irradiating the ethyl acetate solution for 10 h (80%) or the soHd state for 90 h (90%). This reaction was successfully appKed to the adduct 40 of cyclooctatetraene (COT) and p-benzoquinone (92%... 

The photocychzation of the Diels-Alder e do-adducts of cyclic dienes with p-benzoquinone has been successfully applied to the construction of polycyclic cages. Nair et al. reported that the photocychzation of the 2,5-bis(bromomethyl) compound 47 gave the unexpected cage compound 49 as a major product along with the anticipated product 48 (Scheme 9)." The formation of 49 can be explained through the initial photolytic cleavage of the bromine-allylic carbon bond (50) followed by radical reorganization and final bromine radical capture. 

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