Diels-Alder reactions cyclic dienes: furans

Knunyants showed that such perfluoroalkenes, under forcing conditions, undergo Diels-Alder reactions with cyclic dienes such as cyclohexadiene [72] (equation 65) or furan [7J] (equation 66). 

It was first reported in 1996 that indium trichloride catalyzes the Diels-Alder reaction in water [131]. The reaction of acrolein with cyclopentadiene in the presence of 20 mol% InCl proceeds stereoselectively (endo. exo=91 9) (Scheme 8.101). Without catalyst the reaction only goes to 60% completion (endo exo=74 26). The InCh-catalyzed Diels-Alder reaction works with either cyclic or non-cyclic dienes. InCh can be recovered for reuse after the reaction is completed. Indium triflate is also an effective catalyst for intramolecular Diels-Alder reactions of furans under microwave irradiation (Scheme 8.102) [132]. 

Alkenylmethyl) cyclic ethers are formed by the reaction of lactols and alkenes." Diels-Alder reactions. Diethylaluminum chloride deposited on silica seems to be a superior catalyst. Methylaluminum dichloride alone is effective in promoting intramolecular cycloadditions involving a furan ring as the diene. ... 

Several iodonium- and bis(iodonium) norbomadienes and other polycyclic adducts have been synthesized by [2-1-4] cycloaddition reactions of alkynyliodonium triflates with cyclic 1,3-dienes [458,460-464]. In particular, the bis-iodonium acetylene 331 undergoes Diels-Alder reactions with cyclopentadiene 329, furan... 

Other Cyclic Dienes. Besides furan, the Diels-Alder reaction of arynes with other cyclic dienes has been also reported. Tautens etal. have prepared azabicycle 20 from Af-Boc-pyrrole and an aryne intermediate derived from dibromide 19. The prepared cycloadduct has been nsed in the total synthesis of (+)-homochelidonine (Scheme 12.13) [21]. 

Thiete sulfones show an irregular behavior pattern when involved in cycloaddition reactions. With 1,3-dienes, dienamines, enamines, ynamines, diazoalkenes, cyclopropadiene, and its substitution products, furan, and anthracene, the addition proceeds in the normal fashion. With certain Diels-Alder reagents such as tetraphenylcyclopentadienone (tetracycloneX however, the cyclic sulfones react anomalously. The Diels-Alder adducts undergo decomposition with SO 2 and CO extrusion to a seven-membered ring, the tetraphenylcycloheptatriene 223. Bicyclic octadienone is produced as well (Eq. 62). The mechanism of this unusual reaction is proposed by... 

As previously mentioned, short-life cycloalkynes add to reactive dienes such as l,3-diphenylbenzo[c]furan (16) and tetracyclone to give Diels-Alder-type adducts, and the reaction has frequently been used to establish the intermediacy of short-life cyclic acetylenes. The addition reactions have found synthetic applications - > > . The addition of 1-diethylaminobutadienc to cycloalkynes provides an interesting synthetic route for benzo annelation . Intervention of dehydrobullvalene was also confirmed by the formation of DicIs-Alder-type adducts - . At present only azides are used as 1,3 dipoles in the addition reaction with short-life cycloalkynes - - . ... 

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