2- furan, Diels-Alder reaction with methyl acrylate

Flash vacuum pyrolysis of a p-chlorobenzoate ester (35) has also led to useful chemistry <90TL1487>. The reaction produced oxazole-4,5-xylylene (36), which could be trapped with thio-phenol or SO2 to give the corresponding adducts in 39% and 25% yield, respectively (Scheme 5). The unstable intermediate also gave a Diels-Alder adduct with methyl acrylate. The o-xylylene oxazole derivative and the furan analogue were unique among those of several heterocycles studied in that they underwent Diels-Alder reactions instead of polymerization. 

Good yields and high diastereoselectivities were obtained by using zeolites in combination with Lewis-acid catalyst [21]. Table 4.7 illustrates some examples of Diels-Alder reactions of cyclopentadiene, cyclohexadiene and furan with methyl acrylate. Na-Y and Ce-Y zeolites gave excellent results for the cycloadditions of carbocyclic dienes, and combining these zeolites with anhydrous ZnBr2 further enhanced the endo diastereoselectivity of the reaction. An exception is the cycloaddition of furan that occurred considerably faster and with better yield, in comparison with the classic procedure [22], when performed in the presence of sole zeolites. 

Schlessinger and Bergstrom146 reported some asymmetric Diels-Alder reactions of several polystyrene bound furans to which a chiral auxiliary had been attached with methyl acrylate. The adducts were obtained with de values of more than 99%, as was determined after cleavage of the adducts from the resin. 

Scheme 15. Diels-Alder reactions of cyclopropylideneacetates 1-Me, 3-X with furan (57) and 6,6-dimethylfulvene (58) and relative reaction rates compared with methyl acrylate and methyl crotonate [19,46]...

Tetrahydrobenzofurans 173a,b were obtained from the Diels-Alder reaction of 2-(j8-carbethoxyvinyl)furan lh with methyl acrylate and acrylonitrile. 

Asymmetric Diels-Alder reaction.1 The chiral menthyl (S)-3-(2-pyridylsul-finyl)acrylate (1) undergoes [4 + 2]cycloaddition with the furan 2 in the presence of (C2H5),A1C1 at - 20° to give the endo- and exo-adducts 3 in the ratio —2 1, both in about 93% de. The endo-adduct (3) was converted by known reactions to 4, which is opened by lithium hexamethyldisilazide (12,257) to the unsaturated acid in 56% yield. Remaining steps to methyl (- )-triacetoxyshikimate (5) include de-benzylation and acetylation. A similar sequence with exo-2 should provide ( + )-shikimic acid. 

Diels-Alder catalyst This Lewis acid is the most effective catalyst for the reaction of furane with methyl acrylate. The endo/exo ratio is 7 3. Use of Znij results in an endo/ exo ratio of 1 2 (11, 605). 

Privost reaction. A short synthesis of meth shikimate (5) involves base-promoted cleavage of 1, obtained by a Diels-Alder reaction of furane with methyl acrylate (11,... 

BF3 Et20 is the most effective catalyst for the Diels-Alder reaction of furan with methyl acrylate, giving high endo selectivity in the 7-oxobicyclo[2.2.1]heptene product (Eq. 59) [105]. 

In addition, Diels-Alder reactions have also been studied on R-containing micro-porous materials. Murthy and Pillai (1991) reported the reaction of cyclopentadiene, cyclohexadiene or furan with less reactive dienophiles (acrolein, acrylamide or methyl acrylate). They observed that microporous materials give high yields in Diels-Alder reactions although exclusive endoselectivity was only obtained on a combined catalyst (Ce-Y zeolite with anhydrous ZnBr2). 

The Diels-Alder reaction of maleic anhydride with 3,4-dimethoxyfuran affords endo- and exo-adducts at about the same rate, in contrast to furan, where the endo-isomer is the product of kinetic control. In both cases the exo-adduct is thermodynamically more stable. 3,4-Dimethoxyfuran and p-benzoquinone give the eiufo-compound (37), whereas in the reaction with 2,3-dimethyl-1,4-benzoquinone only the exo-adduct (38) was detected. The Diels-Alder adduct (40) of methyl acrylate to 2-amino-3-cyano-4,5-dimethylfuran (39) is readily... 

Diels-Alder Reactions. Bp3-OEt2 is used to catalyze and reverse the regiospecificity of some Diels-Alder reactions, e.g. with pen-hydroxylated naphthoquinones, sulfur-containing conpounds, the reaction of 1-substituted trans-1,3-dienes with 2,6-dimethylbenzoquinones, and the reaction of 6-inethoxy-l-vinyl-3,4-dihydronaphthalene with p-quinones. BFs-OEta has a drastic effect on the regioselectivity of the Diels-Alder reaction of quinoline- and isoquinoline-5,8-dione with piperylene, which produces substituted azaanthraquinones. This Lewis acid is the most effective catalyst for the Diels-Alder reaction of furan with methyl acrylate, giving high endo selectivity in the 7-oxabicyclo[2.2.1]heptene product (eq 35). ... 

Diels-Alder reactions of the o-quinodimethanes (167) and (168) with cyclopentene, cJ5-but-2-ene, norbornadiene, and benzonorbornadiene gave mainly endo-adducts similar behaviour was noted for benzo[c]furan except that the exo-adduct predominated for addition to norbornadiene. " Since it is thought that steric effects for endo- or exo-addition to (167) and (168) are similar, an attractive interaction between endo-alkyl groups and the diene systems is proposed to explain the predominant endo-addition pathway. In contrast to the preference for endo-addition to (167)—(169) by various dienophiles, reaction of l,4-diphenyl-2-benzopyran-3-one (170) leads mainly to the production of exo-adducts. Since 1,3-diphenylinden-2-one also reacted by endo-addition, the exo-selectivity in additions to (170) is explained as resulting from inhibition of attractive endo secondary interactions by non-coplanarity of the phenyl substituents. Related to these results is the finding that isodicyclopentadiene (171) reacts with methyl acrylate under kinetic control to give the syn-adduct (172) a similar result was observed in the addition of methyl... 

---