Diels-Alder-type

An intense purple crystalline solid m.p. 219-220 C. One of the few monomeric cyclo-pentadienone derivatives, most of which spontaneously undergo self Diels-Alder type dimerization. Used as a diene in many studies of various aspects of the Diels-Alder reaction. ... 

Malpass, 1977). Diels-Alder type [2 + 4]-cycloadditions are possible with certain hetero-"ene components (J.R. Malpass, 1977 S.F. Martin, 1980) or with highly reactive o-quinodimethanes as diene components (W. Oppoizer, I978A). 

A large number of Diels-Alder-type reactions, involving both aromatic and sulfonyl isocyanates, have been reported. Heterodienes having high electron density ate found to add to isocyanates to form sis membered heterocycles as shown in Figure 2 (48—50). 

Fig. 2. Diels-Alder-type reactions of aromatic and sulfonyl isocyanates.

Reaction between oxygen and butadiene in the Hquid phase produces polymeric peroxides that can be explosive and shock-sensitive when concentrated. Ir(I) and Rh(I) complexes have been shown to cataly2e this polymerisation at 55°C (92). These peroxides, which are formed via 1,2- and 1,4-addition, can be hydrogenated to produce the corresponding 1,2- or 1,4-butanediol [110-63-4] (93). Butadiene can also react with singlet oxygen in a Diels-Alder type reaction to produce a cycHc peroxide that can be hydrogenated to 1,4-butanediol. 

C-21 dicarboxyhc acids are produced by Westvaco Corporation in Charleston, South Carolina in multimillion kg quantities. The process involves reaction of tall oil fatty acids (TOFA) (containing about 50% oleic acid and 50% hnoleic acid) with acryhc acid [79-10-7] and iodine at 220—250°C for about 2 hours (90). A yield of C-21 as high as 42% was reported. The function of the iodine is apparendy to conjugate the double bond in linoleic acid, after which the acryhc acid adds via a Diels-Alder type reaction to form the cycHc reaction product. Other catalysts have been described and include clay (91), palladium, and sulfur dioxide (92). After the reaction is complete, the unreacted oleic acid is removed by distillation, and the cmde C-21 diacid can be further purified by thin film distillation or molecular distillation. 

The dienamine (148) can react in two ways with methane sulfonyl chloride. In one a 1,4 Diels-Alder-type addition gives 149 in the other way the initially formed product reacts further to give the bis-cyclic sulfone (150) (102,103). 

If the cisoid structure of the dienamine is fixed only the Diels-Alder-type addition occurs (100). 

The types of cycloadditions discovered for enamines range through a regular sequence starting with divalent addition to form a cyclopropane ring, followed by 1,2 addition (i) of an alkene or an alkyne to form a cyclo-cyclobutane or a cyclobutene, then 1,3-dipolar addition with the enamine the dipolarophile 4), and finally a Diels-Alder type of reaction (5) with the enamine the dienophile. 

Enamines have been observed to act both as dienophiles (46-48) and dienes (47,49) (dienamines in this case) in one-step, Diels-Alder type of 1,4 cycloadditions with acrylate esters and their vinylogs. This is illustrated by the reaction between l-(N-pyrrolidino)cyclohexene (34) and methyl t/-a i-2,4-pentadienoate (35), where the enamine acts as the dienophile to give the adduct 36 (47). In a competitive type of reaction, however, the... 

C, Further Reactions of the Diels-Alder Type Adducts... 

Acetylenedicarboxylic acid is known to combine with a number of pyrroles but only in the case of 1-benzylpyrrole have the products been rigorously examined. Mandell and Blanchard showed that in this case a mixture of the maleic anhydride (35), the fumaric acid (36), and the Diels-Alder type adduct (38) was formed. 

Diels-Alder type intermediate as indicated, and there is an analogy in the decomposition of (39) with alkali to (40). 

Cycloaddition Reactions (Diels-Alder Type Reactions). 271... 

A Diels-Alder type [4+2] cycloadditions of 4,5-dihydropyridazine, prepared in situ from its trimer, with 2-methyl- and 2,3-dimethyl-1,3-butadienes (65, R = H, Me R = Me) afforded a complex reaction mixture, from which 6-methyl- and 6,7-dimethyl-3,4,4n,5-tetrahydro-8//-pyrido[l,2-ftjpyridazines (66, R = H, Me R =Me) could be isolated (97CEJ1588). With 1,3-butadiene (65, R = R =H) only a mixture of endo and exo isomers 67 and 68 (R = R =H) was obtained. 

The Michael type reaction of f3/f -5-r-butyldimethysiloxy-3-phenyl-l//-pyrrolo[l,2-c oxa2ole with nitroethylene proceeds in the presence of Lev/is acid to give the alkylated product in good chemical yield and diastereoselecdvity In the case of nitroethylene, the Diels-Alder type transition state is favored to give the ryu-adduct selectively fEq 4 72 ... 

Treatment of l-ethylideneamino-3-methylindole 95 with p-toluene sulfonic acid in boiling benzene gave l,2-dihydro[l,2,4]triazino[l,6-a]indole 96 (75CPB2891). The reaction was said to be due to an initial formation of a Diels-Alder-type adduct followed by the liberation of 3-methylindole. Compound % was oxidized either on exposure to air or by the action of chloranil to give 97 (Scheme 24). 

We have also used poly(propynoic acid) in our studies of the photochemical interaction of PCSs with dienophiles, such as maleic anhydride, tetracyanoethylene, and styrene. This photochemical reaction of Diels-Alder type is accompanied by the breakdown of the conjugation system and the formation of slightly colored adducts266. Together with the cycloaddition reaction, photodegradation of PPA and its adducts takes place. A cycloaddition reaction is always preceded by the formation of a donor-acceptor complex of a PCS with a dienophile. 

Nomura T., Hano Y., Ueda S. Studies on the Optically Active Diels-Alder Type Adducts From Mulherry Tree Int. Congr. Ser. 1998 1157 379 390 Keywords mulberry tree, optically active Diels-Alder type adducts from mulberry tree... 

Ichihara A., Oikawa H. Diels-Alder Type Natural Products - Structures aud Biosynthesis Curr. Org. Chem. 1998 2 365 394... 

Keywords biosynthesis of mulberry Diels-Alder-type adducts, moraceae... 

Scheme 59) [135, 136], It has been proposed that these reactions can be explained as Diels-Alder type additions. These reactivities are similar to those of unstable free disulfur prepared in situ, and different from those of their... 

Catalyst 163 also catalyses the intermolecular [4+2] Diels-Alder-type reaction between alkynes 164 and dienes 165 (Scheme 5.43) [49b], Products 166 were obtained in an excellent regioselectivity and moderate to excellent yields. 

Scheme 5.43 Intermolecular [4+2] Diels-Alder-type reaction between alkynes and dienes...

The formation of cyclic sulfinic esters (sultines) from vinyl sulfenes is known , and the trapping of the expected intermediate vinyl sulfene in the thermolysis of thiete dioxide (6fc and 194) has been convincingly achieved . Specifically, thermolysis of thiete dioxide 6b in the presence of norbornenes gave cycloadducts of the Diels-Alder type (i.e. 252b), resulting from the trapping of the vinyl sulfene formed. The accumulated evidence thus supports the proposed mechanism for these thermolytic reactions. 

P, y-Unsaturated sulfoxides (e.g. 3-thiene oxides) can be prepared by trapping of the in Situ-generated 349 with dienes in a Diels-Alder-type reaction (equation 127) . 

Generation and deazetization of specifically dideuterated azo compound 22 in the presence of methyl (Z)-3-cyanoacrylate (T) gave mixtures of symmetric (S) and unsymmetric (U) Diels-Alder-type trapping products, whose ratio depended on the concentration of Larger [T] gave greater proportions of S-products. The... 

---