Michael-like addition

Other important applications for organoboranes" include the Michael-like addition reaction to a ,/3-unsaturated carbonyl compounds, and the alkylation of a-halogenated carbonyl compounds. 

The 1,4-addition of an enolate anion 1 to an o ,/3-unsaturated carbonyl compound 2, to yield a 1,5-dicarbonyl compound 3, is a powerful method for the formation of carbon-carbon bonds, and is called the Michael reaction or Michael addition The 1,4-addition to an o ,/3-unsaturated carbonyl substrate is also called a conjugate addition. Various other 1,4-additions are known, and sometimes referred to as Michael-like additions. 

The initial product is a dihydroquinoline it is formed via Michael-like addition, then an electrophilic aromatic substitution that is facilitated by the electron-donating amine function. A mild oxidizing agent is required to form the aromatic quinoline. The Skraup synthesis can be used with substituted anilines, provided these substituents are not strongly electron withdrawing and are not acid sensitive. 

Generally, MCRs based on aminoazoles and synthetic precursors of a,p-unsaturated carbonyl compounds proceed via a sequence of Knoevenagel-type condensation, which was already mentioned (see Scheme 3), Michael-like addition, cyclization, and water elimination. For example, the authors of [47] considered the following mechanism (Scheme 9). 

Electron-deficient alkenes, either these with conjugating substituents or of enones, undergo Michael-like additions with regiospecific introductions of the nucleophiles, and this approach has been successful for the formation of cyclopropyl derivatives—notably from some nucleosides. An example involves the addition of the anion of bis(phenylsulfonyl)methane to the phenylselenone 173 which gives the adduct 174 in 35% yield. This reaction presumably occurs by Michael addition to C-2 followed by Sn2 ring-closure reaction at C-3 with displacement of phenylselenic acid. Reductive desulfonylation affords the 2,3,-dideoxy-2,3 -cyclopropayuridine 175.199... 

Both silyl enolates and allylsilanes are excellent nucleophiles for alkylation by other stabilized carbocations such as the tertiary alkyl cations 111 or 112 (Scheme 2.42). Similarly, Michael-like additions, for example, the coupling of 113 with silyl ketene acetal 114, can be also achieved.Owing to the high electrophilicty of the enone system, this reaction proceeds smoothly in polar solvents, even in the absence of Lewis acids. 

Isoxazolidinone 124 was synthesized from dehydroamino acid 123, which has a pentose sugar moiety at its side-chain, by displacement of the terminal mesylate by hydroxylamine with spontaneous cyclization by intramolecular Michael-like addition. Interestingly, when a tetrose-derived dehydroamino acid was substituted, no cyclization was observed. ... 

In the area of 2-enes carrying substituent groups on the double bonds. Michael-like additions have been attempted on the sulphones (19) and (20) with the consequences illustrated in Scheme 11. 

Li G, Jarosinski MA, Hruhy VJ. Diastereospecific tandem Michael-like addition/electrophilic bromination a one-pot tandem asymmetric synthesis of precursors of unusual amino acids. Tetrahedron Lett. 1993 34 2561-2564. 

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