Acyclic carbohydrate-derived dienes

Acyclic carbohydrate-derived dienes have been described by Reitz, Jordan, and Maryanoff. Diene 54, derived from arabinose, underwent cycloaddition to N-phenylmaleimide to give lactone 56 in a yield of 51% 28). A minor isomeric product was also obtained in 16% yield. The major product results from an intramolecular acylation of the initial endo cycloadduct. The stereoselectivity of the addition was found to be consistent with that reported in other studies involving koxy-substituted dienes. 

A review of Diels-Alder reactions of fullerenes with acyclic and cyclic dienes has been presented. The addition of substituted pyrimidine o-quinodimethanes (75) to [60]fullerenes yields novel organofullerenes (76) bearing a pyrimidine nucleus covalently attached to the Ceo cage (Scheme 26). The Diels-Alder dimerization of cyclopenta[/]phenanthrene (77) with isobenzindene (78) yields the dimer (79) in 85% yield (Scheme 27). Further evidence has been supplied to support an early reorganization of the r-network in the dimerization of 2-methoxycarbonylbuta-1,3-diene. The Lewis acid-catalysed Diels-Alder reactions of acrylate derivatives of new carbohydrate-based chiral auxiliaries with cyclohexadiene show excellent endo. exo... 

These developments are here surveyed within the same guidelines as were used previously that is, discrete compounds will be dealt with which have one carbon-carbon multiple bond within the main sugar-chain. As before, enols, enediols, enones, dienes, and dienones will not be considered, nor will unsaturated cyclitols or heterocyclic compounds composed partially of acyclic carbohydrates. The first derivatives having carbon substituents attached by a double bond at a branch-point have now been prepared by application of the Wittig reaction to suitably protected glycosulose compounds these compounds are also arbitrarily excluded, as are ethers or acetals bearing unsaturated substituents. 

The application of cyclic carbohydrate derivatives as chiral dienophiles has been investigated by several groups. 2,3-Dideoxy-DL-pent-2-enopyranose-4-ulose (17) in the thermal [4+2] cycloaddition to the acyclic dienes 18a-c is reported to produce mixtures of cycloadducts 19a-c epimeric on the hemiacetal center with an all-as-configuration of the other newly formed bonds. The reaction with cyclopentadiene (10) and 1,3-cyclohexadiene (11) yields adducts 20 as the sole products31. It should be emphasized that epimerization may occur on the anomeric center during the protection step (as an equilibrium process), thus leading to a mixture of adducts, while the endolexo ratio remains the same. 

The asymmetric hydrocyanation of dienes with substantial enantioselectivities has also been reported (Equation 16.10). Like the reactions of vinylarenes, these reactions have been reported with catalysts containing carbohydrate-derived phosphinites. Reactions of aryl-substituted dienes occur to form the products from 1,2-hydrocyanation. In addition to the reactions of purely acyclic dienes, such as 1-phenyl-l,3-butadiene, dienes containing an exocyclic vinyl group have been studied. These are substrates for products possessing... 

Chiral 1-alkoxy-1,3-dienes derived from carbohydrates have been examined in cycloadditions with azo dienophiles by Stoodley et al. Thereby, reactions with acyclic azo dienophiles were found to be highly selective, leading to optically pure pyridazine derivatives. 

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