Acetals, olefinic, Diels-Alder reaction

Recently Nafion-H was successfully used in the Diels-Alder reaction of olefin acetals with isoprene and cyclopentadiene (Scheme 4.27). The reactions work well in DCM at room temperature and Nafion-H did not cleave the acetal group [96]. The recovered Nafion-H was used four or five times without affecting the yield of the cycloadducts. 

Studies in Lewis acid and LiCi04 (or nafion-H) catalyzed ionic Diels-Alder reactions of chiral and achiral olefinic acetals respectively [96]... 

The Diels Alder reaction of the acyclic diene and 146 may result in unexpected products, however. As reported by Ried, the reaction of 1,4-diphenylbutadiene and 146 may, under drastic conditions, give the aromatized compound (148) and l,3,4,7-tetraphenylbenzo[c]furan (149) in varying amounts, depending on the conditions. In methylglycol/propanol (6 hr reflux) a substance was isolated (mp 147-148°C, 59%) which has tentatively been formulated as 150. One final goal of the sequence described seems to be unaffected by these anomalous reactions, however Diels-Alder adducts of benzo[c]furans can be obtained in a one-step reaction from a diene, 146, and an appropriate olefinic compound in acetic acid/acetic anhydride as shown in Eq. (7). ° ... 

Indium chloride is also an excellent catalyst for ionic Diels-Alder reactions. Acyclic and cyclic olefinic acetals undergo reactions with isoprene and cyclopentadiene in the presence of 20 mol% IrifJ, to form the corresponding cyclic adducts in good yield with good selectivity (Scheme 8.103) [133]. With cyclopentadiene, the endole-xo ratio is fairly good and comparable with that for the LiClO4- and Nafion-H-based reactions. With other Lewis acids, e.g. Yb(OTf)3 or Sc(OTf)5, no cycloadduct is formed. 

Until recently, the reaction of a,/3-unsaturated esters with electron-rich olefins has been reported to afford cyclobutane [2 + 2] cycloaddition products. Amice and Conia first proposed the intermediacy of [4 + 2] cycloadducts in the reaction of ketene acetals with methyl acrylate,108 and the first documented example of the 4v participation of an a,/3-unsatu-rated ester in a Diels-Alder reaction appears to be the report of Snider and co-workers of the reversible, intramolecular cycloaddition of 1-allylic-2,2-dimethyl ethylenetricarboxylates.142 Subsequent efforts have recognized that substitution of the a,/3-unsaturated ester with a C-3 electron withdrawing substituent permits the 4w participation of such oxabutadiene systems in inverse electron demand Diels-Alder reactions with electron-rich olefins. In the instances studied, the rate of the [4 + 2] cycloaddition showed little dependence on solvent polarity [ aeetomtnie/ cycio-hexane — 3, Eq. (15) j acctomtnic toiuene 10, Eq. (20)], and reactions generally... 

Syntheses of 4,5-Unsaturated Cyclic Compounds - Swem oxidation of methyl 2,3,4-tri-C>-acetyl-a-D-glucopyranoside followed by base-induced elimination of acetic acid afforded unsaturated aldehyde 33. Further transformation of the aldehyde group into a methylene unit by way of a Wittig olefination and replacement of the acyl groups with benzyls or methyls yielded 34 which underwent a Diels-Alder reaction (the acyl protected variant of 34 was unreac-tive) with 2-methoxycarbonyl-p-benzoquinone, followed by acid-catalysed double... 

Maleic anhydride grafting (cont.) poly(styrene-co-divinylbenzene), 694 poly(styrene-co-isobutylene), 675, 689 poly(styrene-co-nfialeic anhydride), 676, 679 poly(vinyl acetate), 676, 694 poly(vinyl acetate-co-vinyl fluoride), 678 poly(vinyl alkyl ethers), 675, 679, 692, 701 poly(vinyl chloride), 683, 692, 693, 695, 702 poly(vinylidene chloride), 691 poly(vinyl toluene-co-butadiene), 689 radical—initiated, 459-462, 464-466, 471, 475, 476 radiation—initiated, 459, 461, 466, 471, 474 redox-initiated, 476 rubber, 678, 686, 687, 691, 694 to saturated polymers, 459-466, 475, 476 solvents used 460-463, 465, 466, 469, 474-476 styrene block copolymers, 679 tall oil pitch, 678, 697 terpene polymers, 679, 700 thermally-initiated, 462, 464-467, 469, 476 to unsaturated polymers, 459, 466-474 vapor-phase techniques, 464, 474, 475 to wool fibers, 476 Maleic anhydride monomer acceptor for complex formation, 207-210 acetal copolymerization, 316 acetone CTC thermodynamic constants, 211 acetone photo-adduct pyrolysis, 195, 196 acetylacetone reaction, 235 acetylenic photochemical reactions, 193-196 acrylamide eutectic mixtures, 285 acylation of aromatic acids, 97 acylation of aromatics, 91, 92 acylation of fused aromatics, 92, 95, 97, 98 acylation of olefins, 99 acylation of phenols, 94-96 acylic diene Diels-Alder reactions, 104-111, 139 addition polymer condensations, 503-505 adduct with 2-cyclohexylimino-cyclopentanedi-thiocarboxylic acid, 51 adducts for epoxy resins curing, 507-510 adduct with 2-iminocyclopentanedithiocarboxylic acid, 51... 

Olefinic pyrazines like 108 were shown to react with QH in the superacid TfOH to give anti-Markovnikov addition products like 109 <050L2505>. The orientation observed is presumed to be due to the multiply charged heterocycle adjacent to the olefin. Pyrazine o-quinodimethanes underwent Diels-Alder condensation with meso-tetraarylporphyrins to give new jt-extended porphyrins <05TL2189>. A one-pot formation of polycyclic - and -lactones like 111 was developed using the reaction of pyridine and pyrazine (110) with bis(trimethylsilyl)ketene acetals. Many of them were characterized by X-ray <05EJO3724>. 

The reported thermal [4 + 2] cycloaddition of arylmethylenemalon-dialdehydes with electron-rich olefins including enol ethers, ketene acetals, enamines, and cyclopentadiene (benzene, 25°C) or their Lewis acid-catalyzed reaction with simple olefins including isobutylene and 1,1-diphenylethylene (Znl2 catalyst, benzene, 25°C) further illustrates the Diels-Alder rate acceleration accompanying the substitution of an ,/3-unsaturated aldehyde with a C-3 electron-withdrawing group [Eq,... 

---