Thermal Michael reaction

Mannich bases read wilh ketones tvithout basic catalysts to give 1.5-dikctoncs. but this process, known as the thermal-Michael reaction, has a different mechanism Brown Buchanan Curran McLay Tetrahedron 1968,24. 4565 Gill James Lions Potts/. Am. Chem. Soc. 1952, 74, 4923. 

Angelo, J. Desmaele, D. Dumas, R Guingant, A. Tetrahedron Asymmetry 1992, 3, 459. i046Mannich bases react with ketones without basic catalysts to give 1,5-diketones, but this process, known as the thermal-Michael reaction, has a different mechanism Brown, H.L. Buchanan, G.L. Curran, A.C.W. McLay, G.W. Tetrahedron 1968, 24, 4565 Gill, N.S. James, K.B. Lions, R Potts, K.T. J. Am. Chem. Soc. 1952, 74, 4923. 

In those instances where the thermal Michael reaction is sluggish due to sterically hindered substrates, the use of high pressure (15 kbar, or of LiClOa (3 mol% in CH2Cl2 or... 

Reaction of phenyl vinyl ketone with cyclopentanone under thermal conditions resulted in a diastereomeric mixture of 1,5,9-triketones 374 via a double Michael reaction. Treatment of this mixture with ammonium formate in polyethyleneglycol-200 under microwave irradiation conditions led to the very fast and efficient formation of a 2 1 diastereomeric mixture of cyclopental flquinolizidines 375 and 376 <2002T2189>. When this reductive amination-cyclization procedure was carried out starting from the purified /ra r-isomer of 374, the result was identical to that obtained from the cis-trans mixture, showing the operation of thermodynamic control (Scheme 86). 

Michael, G. Al-Siri, M. Khan, Z. H., and Ah, F. A., Differences in Average Chemical Structures of Asphaltene Fractions Separated From Feed and Product Oils of a Mild Thermal Processing Reaction. Energy Fuels, 2005. 19 pp. 1598-1605. 

Bismaleimides - Bismaleimides resins were first introduced into the market in the early 1970 s. As with other resin systems, there are many variations of bismaleimides. The Kermid and Kinel bismaleimide products as marketed in the U. S. by Rhodia are representative examples. Bismaleimide chemistry is represented in Eq. 3 where curing can be accomplished thermally through the unsaturation in the maleimide or by way of the Michael Reaction where an appropriate curing agent such as aromatic diamine adds across the activated double bond. In most instances, a combination of curing thermally through the double bond and via an aromatic diamine is used in actual practice. Bismaleimides are frequently formulated... 

The cycloaddition of azides to multiple -ir-bonds is an old and widely used reaction. Organic azides are well known to behave as 1,3-dipoles in thermal cycloaddition reactions.178 The first example of this reaction was observed by Michael in 1893.179 Since then the addition of azide to carbon-carbon double and triple bonds has become the most important synthetic route to 1,2,3-triazoles, -triazolines and their derivatives.180-184 The cycloadditions of simple organic azides with electron-rich dipolarophiles are LUMO controlled.3 Since the larger terminal coefficients are on the unsubstituted nitrogen in the azide and unsubstituted terminus in the dipolarophiles, the 5-substituted A2-triazolines are favored, in agreement with experiment.185-187 Reactions with electron-deficient dipolarophiles are HOMO controlled, and... 

Phenoxypropanoic acid, 3-(phenylthio)propanoic acid, 4-phenylbutanoic acid and the corresponding ethyl and methyl esters have been pyrolysed between 520 and 682 K.10 Analysis of the pyrolysates showed the elimination products to be acrylic acid and the corresponding arene. The thermal gas-phase elimination kinetics and product analysis have been found compatible with a thermal retro-Michael reaction pathway involving a four-membered cyclic transition state. 

The Michael reaction of silyl enol ethers with a,P-unsaturated ketones (enones) has generally been performed with the aid of a stoichiometric amount of Lewis acid to afford 1,5-dicarbonyl compounds 80,81). When the reaction was conducted thermally in acetonitrile (82), under high pressure (Si), or by the catalytic use of (Me2N)3S MesSiFj" (84) or Ph3C CI04 (S5), the intermediate adducts were isolable in the form of synthetically valuable silyl enol ethers. 

Recently, Wasserscheid and co-workers [103] introduced a complementary method for functionalized ionic liquid synthesis (11). In a one-pot, two step synthesis, the protonation of an imidazolium or pyridinium cation followed by a Michael-type addition to methyl vinyl ketone was reported. The only drawback is the limited thermal stability of the cations, which at moderately elevated temperatures undergo a retro-Michael reaction ... 

In addition to the side reactions mentioned above, deamination of Mannich bases can occur, especially at elevated temperature, to give a,p-unsaturated derivatives. This route of decomposition of Mannich bases has been exploited as a means of in situ generation of a,p-unsaturated ketones in the Michael reaction and for the direct synthesis of a,3-unsaturated ketones several reviews of the Mannich reaction have discussed aspects of these applications.Recently, a direct one-pot synthesis of a-methylene ketones has been reported involving condensation of ketones with formaldehyde and A -methylaniline tri-fluoroacetate in aptotic solvents. Also, a less direct method has been described in which Mannich bases prepared from 3-keto esters, formaldehyde and dimethylamine are subjected to quatemarization and thermal fragmentation to yield a-methylene ketones.This method is particularly useful for the regios-pecific synthesis of a-methylene ketones because the aminomethylation reaction always takes place at the most activated position flanked by the ketone and ester groups. 

Thus, if the amino acid (Figure 8.23) is alanine (R3 = -CH3), widely represented in must and wine, the corresponding aldehyde is ethanal. If the amino acid is methionine (R4 = CH3-S-CH2-CH2-), which is certainly only present in small quantities but is reputed to be highly reactive with carbonylated compounds, then methional, or -methyl-S-propanal, is produced. This compound is thermally unstable and evolves rapidly, via a Retro-Michael reaction, into acrolein and methanethiol (Figure 8.28). These smell of cooked cauliflower, wet dog, etc. In wine, part of the methional returns to methionol via catalyzed reduction by alcohol dehydrogenase with NADH. 

The [2+2] cycloaddition is the main method for the synthesis of cyclobutanes and 4-membered ring heterocycles. The thermal reaction between two alkenes is not a synchronous, pericyclic process, which is symmetry forbidden, but is a two-step, Lewis acid-catalysed procedure involving a Michael reaction between an electron-rich alkene and an electron-poor partner followed by cyclisation (Figure 8.7). 

Lange and his co-workers have reported a short, convenient approach to the sesquiterpene (—)-acorenone (170) centred about the stereoselective Michael addition of l-methoxybut-3-en-2-one to the less hindered face of the enamine (169) followed by aldol cyclization, ° and Oppolzer etal. have synthesized acorenone and several other members of the same sesquiterpene family by further elaboration of the cis,trans mixture of esters (171) formed, with 100% cndo-selectivity, during the intramolecular thermal ene reaction of the 1,6-diene (172). ... 

HigMy branched polymeric materials with large number of end groups can offer unique physical properties. Dendrimers (described in Chap. 1) differ from linear polymers in viscosity and thermal behavior. A variety of applications have been forecast for these highly branched globular macromolecules. One early approach to dedrimer synthesis relied upon the Michael reaction using repeated sequential additions of an amine to a,(3-unsaturated ester [248] ... 

Show the product formed from each Michael reaction in the solution to Example 15.10 after (1) hydrolysis in aqueous NaOH, (2) acidification, and (3) thermal decarboxylation of each /3-ketoacid or /3-dicarboxylic acid. These reactions illustrate the usefulness of the Michael reaction for the synthesis of 1,5-dicarbonyl compounds. 

Show how the series of reactions in Example 15.10 and Problem 15.10 (Michael reaction, hydrolysis, acidification, and thermal decarboxylation) can be used to prepare 2,6-heptanedione. 

Show the outcomes of subjecting the Michael reaction products in Problems 15.36a and 15.36b to hydrolysis, followed by acidification, followed by thermal decarboxylation. (See Example 15.11)... 

TEA (trifluoroacetic add) 65, 538, 580 TFAA (trifluoroacetic anhydride) 879 TFE (trifluoroethanol) 593 TFPB (tetrakis[3,5-bis(trifluoromethyl) phenyljborate) 434 Theonella cf. swinhoei 1352 thermal effect 581, 593 thiazolium salts 498 thio-Michael addition 52 thio-Michael reaction 1005 a-thio-substituted furanones 178 thioamides 109... 

C) is necessary for the photochemical reaction to compete with thermal Michael addition. The mechanism of the reaction is presumed to involve ET-sensitized addition to yield P-aminoesters, followed by thermal cyclization to yield the lactams. The use of acrylonitrile in place of methyl acrylate affords more complex product mixtures, resulting from trapping of the intermediate radical adducts by acrylonitrile. 

---