Michael addition cascade reactions

Keywords Sulfonamides, vinyl ketones, toluene, DBU, room temperature, Michael addition, cascade reaction, cyclization, functionalized 3-aroyl-4-hydroxy-4-arylpiperidines, stereoselectivity... 

The mechanism of these MCRs involving Meldrum s acid should include Knoevenagel condensation and Michael addition cascade process [100, 113] (Scheme 37). To form positional isomeric reaction product, arylliden derivatives of Meldrum s acid are attacked by exocyclic NH2-group instead of endocyclic nucleophilic center. 

Palladium chemistry has been used in the synthesis of tetrahydroisoquinolines. Different combinations of iodoaryl-amine-alkene can be used in these multicomponent reactions. For example, the metal-mediated o-alkylated/alkenyl-ation and intramolecular aza-Michael reaction (Scheme 109) give moderate yields of heterocycle <2004TL6903>, whereas the palladium-catalyzed allene insertion-nucleophilic incorporation-Michael addition cascade (Equation 172) produces good yields of tetrahydroisoquinolines in 15 examples <2003TL7445> with further examples producing tetrahydroquinolines (Scheme 110) <2000TL7125>. 

In 2013, the Hui group developed an efficient NHC-catalyzed stereoselective aza-Michael-Michael-lactonization cascade reaction of 2-amino phenyl-enones and 2-bromoenals. Functionalized tetrahydroquinolines with three consecutive stereogenic centers were obtained in high yields with excellent diastereo- and enantioselectivity. This approach is attractive due to the mild reaction conditions and the potential application of the products in medicinal chemistry. In addition, this strategy extends the scope of NHC catalysis and provides a simple protocol for the NHC-catalyzed cascade reaction (Scheme 7.100). 

In 2(X)9, Hayashi and co-workers [52] developed a Michael-Knoevenagel cascade reaction between enals and dimethyl-3-oxoglutarate (79) furnishing cyclohexenes (80) in good yields and enantioselectivities. In this case, the absence of base allows the single addition of one molecule of dimethyl-3-oxoglutarate to the enal. 

A BINAP-derived bifunctional thiophosphoramide gives >98% del>99% ee in Michael addition of cyclohexanones to both aryl- and alkyl-substituted nitroolefins. Imidazolylmethyl ketones undergo one-pot Michael-aldol cascade reactions with Q ,/3-unsaturated aldehydes in DCM at 20 °C using the simple organocatalyst, prolinol... 

A combination of Michael addition, Mannich reaction, and intramolecular condensation allowed Xu and coworkers to get a quite facile access to tetrahydropyridines 165 with C3 all-carbon quaternary stereocenters in moderate yields and good optical purity (up to 74% ee) [79], The developed organocatalytic enantioselective multicomponent cascade reaction relies on the catalytic ability of the simple (5)-proline (1) that quickly reacts with the intermediate A, generated in turn via a Knoevenagel reaction between the p-ketoester 91 and formaldehyde 65. The resnlting iminium ion B undergoes the nucleophilic attack of a second moiety of p-ketoester 91 prodncing the Michael adduct D. Such intermediate enamine is then involved in the Mannich reaction with the imine E (dne to the in situ condensation between primary amine 51 and formaldehyde 65) to furnish the advanced intermediate F, which after an intramolecular condensation releases the (5)-proline (1), and the desired prodnct 165 (Scheme 2.52). 

Scheme 1.40 Silylated biphenylprolinol-catalysed triple cascade Michael addition-Michael addition aldol reactions.

In 2011, the Fukuyama group reported the first total synthesis of (-)-conophylline, whose structure consists of two pentacyclic aspidosperma skeletons (Scheme 13.5) [6]. The two aspidosperma skeletons were both constructed through a similar intramolecular Michael addition/Mannich reaction cascade stfategy, which could produce three new rings and three new stereogenic centers with complete stereoselectivity in just one step. 

Balme G, Bouyssi D, Monteiro N (2006) The Virtue of Michael-Type Addition Processes in the Design of Transition Metal-Promoted Cyclizative Cascade Reactions. 19 115-148 Barluenga J, Rodriguez F, Fanands FJ, Fldrez J (2004) Cycloaddition Reaction of Group 6 Fischer Carbene Complexes. 23 59-121 Basset J-M, see Candy J-P (2005) 16 151-210... 

Keywords Absolute configuration, Amines, Amino acids, Carbenes, Cascade reactions, 2-chloro-2-cyclopropylideneacetates. Combinatorial libraries. Cycloadditions, Cyclobutenes, Cyclopropanes, Diels-Alder reactions. Heterocycles, Michael additions. Nitrones, Nucleophilic substitutions, Peptidomimetics, Palladium catalysis. Polycycles, Solid phase synthesis, Spiro compounds. Thiols... 

The first highly regio-, chemo-, diastereo-, and enantio-selective vinylogous Michael addition of oqa-dicyanoalkenes to oq/S-unsaturated aldehydes employs salts of a,a-diarylprolinol (103) (20 mol%) as organocatalysts. The reaction presumably involves the formation of an iminium species from the aldehyde as the first step of the cascade.153... 

Diastereo- and enantio-selective cascade of Michael addition and lactonization between various silyl enolates derived from phenyl carboxylates and -unsaturated ketones were successfully carried out by using an efficient organic catalyst, a cinchoni- dine-derived chiral quaternary ammonium phenoxide. In this asymmetric domino reaction, the corresponding tnms-3,4-dihydropyran-2-oncs were obtained in high yields with almost complete diastereoselectivities and good to excellent enantioselectivities.161... 

The isolation of an intermediate revealed that the reaction proceeds via a tandem Mannich-Michael addition pathway. The zinc (II) chloride-promoted cascade reaction starts with a Mannich reaction. For a number of reactions, the Mannich-type intermediate can be isolated if the reaction is stopped by addition of diluted ammonium chloride solution [52,53]. 

Poly(amidoamine)-(PAMAM-Starburst)-Monodendrons Among the first Starburst (Cascade) syntheses we performed in the early 1980s [83] involved partially masked (differentiated) initiator cores. For example dodecyl-amine, hydroxyalkyl amines or partially protected alkylene diamines were used as initiator cores and submitted to sequential (a) Michael addition with methyl acrylate followed by (b) reaction with an excess of ethylene diamine to give in situ branch cell construction in a divergent manner. The resulting products were core functionalized monodendrons as shown below ... 

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