Diels-Alder reacdon

Dehydration of fi-nitro iilcohols provides an important method for the preparation of nitroalkenes. Because lower nitroalkenes such as nitroethylene, Tnitro-Tpropene, and 3-nitro- Tpropene tend to polymerize, they must be prepared careftdly and used immediately after preparation. Dehydration v/ith phthalic anhydride is the most reliable method for such lower nitroiilkenes. Such lower nitroalkenes have been used as important reagents for Michael acceptors or dienophiles in the Diels-Alder reacdon, which v/ill be... 

The Diels-Alder reacdon followed by radical denitradon provides a nseftd strategy for constnicdon of six-membered compounds, in which thenitro group accelerates the reacdon and also controls the reglo-chemistry of the addidon fEq. 7.75. ... 

The intramolecnlar Diels-Alder reacdon i presence of LiClO in diethyl ether to give oi group is removed from the adduct v/ith Bn- SnH fEq. 7.76. ... 

Ono and coworkers have devised a new acetylene eqidvalent for the Diels-Alder reacdon namely, l-phenylsulfony-2-nitrQethylene is a very reacdve dienophile, and the radicM eliminadon from the adduct gives the Diels-Alder adduct of acetylene, as exemplified in Eq. 7.113. " " Other acetylene eqidvMents are summarized in a review. 

Acetylene eqrrivMent of fi-sulfonylnitroalkenein the Diels-Alder reacdon is used in part for totiil synthesis of pancradstadn lEq. 7.114. Pancradstadn is isolated from the root of the plant Pcuicraiiion liiwraU Jacq., nadve to Hawaii, which exhibits and-cancer acdvity. 

Node and coworkers have used this aromadzadon strategy for the synthesis of (-) aphanor-phineThe Diels-Alder reacdon of chiral nitroalkene, prepared by the asymmecdc nitrooleft-nation reacdon of ct-methyl-o-valerolactone, with the Danishefsky s diene followed by aromadzadon is used as a key step for this total synthesis, as shown in Scheme 8 6... 

Nitrodienes are conveniendy prepared by eliminadon of benzoic acid from fi-nitro-fi- Tcy-clopentenyl-ct-benzoyloxyethane They undergo the Diels-Alder reacdon with methyl actylate fEq 8 17 ... 

In intramoleculdf Diels-Alder reacdons, two rings are formed in one step The reacdon has been used to synthesize a number of interesting ring systems" The intramolecular cyckzadon of fE -l-nitrodeca-l,6,8-triene at 80 C affords an endo cycioaddnct with the irons ring fusion preferendally, as shown in Eq 8 18 In contrasr, fZ -nitroalkenes produce a nearly I T mixture of cis- and rrruii -hised cycioaddncts ... 

Although Lewis acid-catalyzed-Diels-Alder reacdons of enones are common, there are few repoiTS on the catalysis of Dieis-Alder reacdon of nltroalkenes The reacdon of nltroalkenes with alkenes in the presence of Lewis acids undergoes a different course of reacdon to give cyclic nltronates fsee Secdon 8 3 Knochei repotted an enhanced reacdvity and seiecdvity of the intramolecular Dieis-Alder reacdon using silica gei as Lewis acid in hexane fEq 8 19 ... 

DinitrQ-ll-Qxatricyclo[6 2 1 0 undec-9-ene has been prepared by an intramolecular Diels-Alder reacdon of the furan with a idtroalkene group as shown in Eq 8 26 This tricyclic compound is a versatile synthedc tool for the preparadon of ergot alkaloids... 

A typlciil regioselecdvity and endo/exo selecdvity has been reported in the Diels-Alder reacdon of 2-W-acylamino -l,3-diene v/ith nitroalkenes fEq 8 21) Thus, exo products are predominandy formed, which is generiil for the Diels-Alder reacdon of nitroalkenes v/ith sterically hmdered dienes... 

The totiil synthesis of frodosinB, which isapotendally usefiddnigfor HIV, has been reported fScheme 8 8 The key steps in the synthesis are a Friedel-Crafts reacdon to form the seven-membered ring and a Diels-Alder reacdon of nitroethylene to biuld the six-membered ring, thereby fixing the double bond in the proper posidon ... 

Thepreparadonof resin-bound nitroalkenes via a micro wave-assisted Knoevenagel reacdon of resin-bound nitroacedc acid v/ith aryl and alkyl subsdnited Mdehydes is reported. The potendiil of these resin-bound nitroalkenes for apphcadon in combmatorlM chemistry is demonstratedby a Diels-Alder reacdon v/ith 2,3-dimethylbutadienefScheme 8 9) Iris Mso used for one-pot three-component tandem [4t-2 /[3t-2 reacdons v/ith ethyl vinyl ether and styrene... 

Asyrrunetiic Diels-Alder reacdons using chuMsulfinylalkenes have been extensively snidied by Koiziuru and coworkers Fuji and coworkers have extended this strategy to chirM 1-falkyl-sulfinyl -2-nitroalkenes Such nltroalkenes react v/ith reacdve dienes such as Danishefsky s dienes to produce an adduct v/ith a high enandomeric excess fee fsee Eqs 8 34 and 8 35 ... 

Denmark and coworkers have developed an elegant method for generating cyclic ni using niiroalkenes as heterodienes in the Diels-Alder reacdon fEq. S.7S. The synthedc utility of this reacdon is discussed in Secdon S.3. 

Hetero Diels-Alder reacdons using nitroalkenes followed by 1,3-dipolar cycloaddidons provide a nsefid strategy for the constnicdon of polycychc heterocycles, which are found in naturM products. Denmark has coined the term tandem [4t-2 /[3t-2 cycloaddidon of nitroalkenes for this type of reacdon. The tandem [4-i-2 /[3-i-2 cycloaddidon can be classified into font famihes as shown in Scheme 8.31, where A and D mean an electron acceptor and electron donor, respecdvely. " In generril, electron-rich alkenes are favored as dienophdes in [4-i-2 cycloaddidons, whereas electron-deficient alkenes are preferred as dipolarophdes in [3-i-2 cycloaddidons. 

Anovelsynthedc approach toward the AB-ring system of9-azasteroids using the Diels-Alder reacdon of nitroalkene and subsequent reducdve cyclizadon has been shown fScherae 10.24. ... 

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