Acrylates Lewis acid catalysis

The other class of acrylic compatible tackifiers includes those based on ter-penes. Terpenes are monomers obtained by wood extraction or directly from pine tree sap. To make the polyterpene tackifiers, the monomers have to be polymerized under cationic conditions, typically with Lewis acid catalysis. To adjust properties such as solubility parameter and softening point, other materials such as styrene, phenol, limonene (derived from citrus peels), and others may be copolymerized with the terpenes. 

Asymmetric Diels-Alder reactions. The acrylate of (+ )-l is markedly superior to ( —)-menthyl acrylate in effecting asymmetric induction in Diels-Alder reaction with cyclopentadiene (Lewis acid catalysis, equation I). A chiral intermediate in Corey s prostaglandin synthesis was obtained by the reaction of (-1- )-8-phenylmenthyl acrylate with a cyclopentadiene derivative.1... 

The living polymerization of acrylates by GTP does proceed under Lewis acid catalysis [14]. ZnCl2 or ZnBr2 are effective but require concentrations of catalyst at a level of 10% based on monomer. R2A1C1 works at lower levels. However, HgCl2 activated by TMS iodide is the best Lewis acid system and... 

The major interaction between these two molecules is between the nucleophilic end of the exo-cyclic alkene and the electrophilic end of the acrylate. These atoms have the largest coefficients in the HOMO and LUMO, respectively, and, in the transition state, bond formation between these two will be more advanced than anywhere else. For most ordinary alkenes and enophiles, Lewis acid catalysis to make the enophile more electrophilic, or an intramolecular reaction (or botft is necessary for an efficient ene reaction. 

The effects of Lewis acids on regioselectivity are shown by the reaction of piperylene with methyl acrylate giving mainly the ortho adducts 6.203, as usual, but this preference is increased with Lewis acid catalysis. Similarly, as an... 

Cycloaddidons of 2-triethylsilyl- and 2-tributylstannyl-13-butadienes (172) to ethyl acrylate and methyl vinyl ketone also proceeded with moderate regioselectivities which could significantly enhanced by Lewis acid catalysis in favor of products (174) (Scheme 41, Table 2). The resulting cyclo-hexenylstannanes (174 M = SnBua) show potential for C—C coiq>ling reactions. 

The reaction did not require dry solvents or inert atmosphere and afforded the desired adducts in 42-98% yield. As expected, the more reactive acrolein and methyl vinyl ketone gave very good results with both acyclic and cyclic p-ketoesters and p-diketones and, surprisingly, acrylonitrile and methyl acrylate, reported to be totally inactive under Lewis acid catalysis, " afforded the corresponding adducts with a-acetylbutyrolactone in high yield (77 and 98% respectively). In the reaction with crotonaldehyde, a 1 1 mixture of... 

Furan also undergoes cycloadditions with allenes and even with simpler dienophiles, like acrylonitrile and acrylate (specifically enhanced by the presence of zinc iodide),and with maleate and fumarate esters, if the addition is conducted under high pressure. This device can also be used to increase markedly the reactivity of 2-methoxy- and 2-acetoxyfuran towards dienophiles. Lewis acid catalysis can also been used to accelerate furan Diels-Alder additions. At higher reaction temperatures alkynes and even electron-rich alkenes will add to furan. 

Electron-rich 2//-thiopyrans react readily with reactive dienophiles such as maleic anhydride, generally giving the endo adduct in good yield. However, less reactive dienophiles such as acrylates requires catalysis to prevent the need for elevated temperatures which may cause decomposition of the thiopyran. Lewis acids facilitate such reactions which can exhibit high stereoselectivity. Thus 4-tri- z>propylsilyloxy-2//-thiopyran shows a preference for the exo... 

Catalysis Act as Lewis acids to catalyze reactions Manufacture of acrylates, methacrylates, polyamides, polyester, polyurethanes, epoxies, etc. 

Thiopyrans also behave as dienes in DielsAlder reactions, though less reactive dienophiles such as acrylates require catalysis by a Lewis acid to prevent the need for the elevated temperatures which might cause decomposition of the thiopyran (Scheme 79). Thus, thiopyrans can serve as equivalents for (unreactive) /xf-dicncs, since desulfurization of adducts is easy, e.g., <1991CJC1487>... 

An alternate to the use of Lewis acids is the employment of amine catalysts in the MBH reaction. Hatakeyama and coworkers have used the quinidine (7.164) as a catalyst in the MBH reaction of both aromatic aldehydes such as ben-zaldehyde (7.17) and aliphatic aldehydes with the acrylate (7.165). In all cases ees are high (91-99%), but yields are moderate. This amine has also been applied to the catalysis of the aza-Bayhs-HiUman reaction of methylvinyl ketone (MVK) and methyl acrylate with N-tosylarylaldimines giving the product with high ee. ... 

In the case of catalysis by Lewis acids found to be suitable for acrylates, the mechanism is completely different and propagation occurs by monomer activation. 

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