Bicyclic compounds from Diels-Alder reaction

Indole-2,3-quinodimethanes [44] 44 are bicyclic outer-ring dienes that are widely used to prepare a variety of heterocyclic polycyclic compounds. These dienes, generated by extrusion of CO2 from lactones, are then trapped by dienophiles. Some examples of Diels Alder reactions of the dienes 44 are reported in Scheme 2.19. 

The reactions include an unusual Diels-Alder reaction and a very useful synthetic method, the dechlorination of polychlorinated compounds. At the present time this procedure is the best one available for the removal of chlorine from an organic molecule. The end product, 7,7-dimethoxybicyclo[2.2.1]heptene, is an interesting and useful intermediate in bicyclic chemistry it has a reactive double bond and a protected carbonyl group in the 7-position. 

The cyclobutene (310) opened at 100 °C to facilitate the intramolecular Diels-Alder reaction, from which the m-fused bicyclic compound (311) was isolated 108). 

Ihrig 6S> studied a series of rigid bicyclic compounds (5-8) obtained from the Diels-Alder reaction of hexachlorocyclopentadiene with fluoroethylenes. In... 

The first product of the reaction of 1,2,4,5-tetrazines (39) with alkenes (142) is the bicyclic compound (143), which has never been isolated since it loses nitrogen immediately by a retro-Diels-Alder reaction to give 4,5-dihydropyridazine (144). These compounds have been isolated in a few cases but usually a product is obtained which is formed from (144) in one of four different ways ... 

Linear tricyclic systems have been obtained from intramolecular photocyclization of l,2-dihydropyridin-2-one to give an olefinic bicyclic product and subsequent Diels-Alder reaction with an acyclic dienophile to give the tricyclic compound. Reactions of this type have been mentioned in Sections 2.04.6.3 and 2.04.7.2. 

They also reported the intramolecular version of this asymmetric Diels-Alder reaction [53]. ( , )-Trienecarboximides of type 45 derived from chiral oxazolidones undergo Me2AlCl-catalyzed intramolecular Diels-Alder reactions affording bicyclic compounds 46 with high endo and diastereoselectivity (endolexo = -100 1). The stereochemistry is controlled by the stereogenic center at C4 of the chiral auxiliary (Xc) (Sch. 29). 

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