Michael addition definition

Chemists usually learn about reactions according to fiinctional groups for example, How can I make an aldehyde and what reactions are known for aldehydes " This is clearly not a very good starting point for classifying reactions. The poor state of affairs in the definition of reaction types is further quite vividly illustrated by the fact that many chemical reactions are identified by being named after their inventor Diels-Alder reaction, Michael addition, Lobry-de Bruyn-van Ekenstein rear-... 

More serious limitations and precautions apply to compounds in which not all three R, R, and R" groups are aromatic. Autocondensation of benzylideneacetone (111) yields an unstable chloroferrate which may be 113 or 115, according to whether a Michael addition to 112 or a crotonic condensation to 114 is first involved. Since compound 113 could readily be prepared from 2,6-dimethyl-4-phenylpyrylium and benzaldehyde, the structure of the reaction product should be easily soluble. Another equivocal product is formed from two moles of benzylideneacetone, but a definite structure (116) results from chalcone and benzylideneacetone. ... 

Reactions of this type are referred to in a variety of terms, many of which are rather confusing and nondescriptive. They sometimes are classified as 1,4-additions, implying that addition occurs across the terminal positions of the conjugated system. A synonymous term is conjugate addition. When the nucleophile is a carbanion, the reaction is called a Michael addition. Thus, by this definition, Equation 17-7 represents a Michael addition. Another, perhaps more typical, example is the addition of an enolate to a conjugated ketone ... 

The second mechanism would result from the stepwise addition of two allysines and lysine to form dehydromerodesmosine (via Michael additions) and then condensation with a fourth allysine residue. The major problem in resolving these points is the difficulty of sequencing around intra- and intermolecular crosslinks in a manner to provide definitive information. 

Markovnikov orientation the 1,2-addition of an unsymmet-rical electrophilic reagent to an alkene with attachment of the more positive moiety of the reagent (H in the original definition) to the less substituted carbon Michael addition conjugate addition addition of a nucleophile to the /3-position of a carbon-carbon double or triple bond that is conjugated to a carbonyl or other electron-withdrawing group... 

The second chapter, by David A. Oare and Clayton H. Heathcock, deals with the stereochemistry of uncatalyzed Michael reactions of enamines and of Lewis acid catalyzed reactions of enol ethers with a,/ -unsaturated carbonyl compounds. It is effectively a continuation of their definitive review of base-promoted Michael addition reaction stereochemistry that appeared in the preceding volume of the series. 

Given the definitions of the four kinds of attachment to a carbon site, any reaction at that site may be described as the replacement of one kind of attachment by another. Thus a reaction at a single carbon site may be symbolized by a pair of the capital letters (77, R, H, Z), the first indicating the attachment formed in the reaction and the second the attachment removed. For example, HZ is a replacement of a heteroatom by hydrogen, i. e. a reduction of halide, ketone etc. It is trivially easy to extend this notation to reactions that occur at more than one carbon site. For example, an aldol-type reaction is described as RH.RZ, and a Michael addition as RH.R77,H77 in an obvious notation. 

As initially stated, the definition of multicomponent reaction could be extended also to those reactions that implicate the addition of further reagents only after a suitable time from the very beginning of the procedure. Among others, few Chinese groups reported two notable examples of one-pot Michael addition/Pictet-Spengler cyclization sequence. In particular, in 2011, Zhao et al. developed a high enantioselective organocatalytic synthesis of several... 

However, diastereoselective transformations like this are not to be discussed within this monograph, as they do not fulfill the criteria of asymmetric synthesis, according to Marckwald s definition (in today s language) this would mean [...] those reactions, or sequences of reactions, which produce chiral nonracemic substances from achiral compounds with the intermediate use of chiral nonracemic materials, but excluding a separation operation [35]. Thus, diastereoselective conversions not included for that reason in this book are, for example, aldol additions, Mannich reactions, and Michael additions of enolates to ketones, imines, and cx,P-unsaturated carbonyl compounds, respectively, with any chiral skeleton. For such stereoselective enolate reactions that are not asymmetric syntheses, the reader is referred to the literature, which treated this topic in a comprehensive manner [36]. 

An accessory proposal was Arthur Michael s hypothesis that many reactions proceed by addition, for example, a polymerization of acetaldehyde (CH3CH = O) in the presence of bases (OH) to an aldol (CH3CHOHCH2CHO), with subsequent loss of water to form crotonaldehyde (CH3CH = CHCHO). Michael, educated in America, Germany, and France, made use of Kekule s idea that two molecules may form a "polymolecule" or molecular compound, which, in turn breaks up to yield the final products.33 Lachman expressed fairly standard misgivings about this proposal of an intermediary and transition form "If we are going to explain reactions by means of addition products which we do not or cannot isolate, our explanation loses its definiteness. It becomes simply a possible explanation, and its conclusions are by no means binding."34... 

It seems appropriate to inquire whether or not it is possible to carry out other Michael reactions and, generally, other nucleophilic additions to unsaturated compounds as a sequence of kinetically independent steps using one s choice of nucleophiles and electrophiles The answer is definitely yes . A rationale similar to that used to describe the Robinson annulation provides us with the key to how this goal may be attained. First of all, the initial step of the reaction, addition of the nucleophilic component across a double (or triple) bond, needs to be carried out in the absence of the external electrophiles (preferably in aprotic solvents). Secondly, a carbanionic intermediate, incipiently formed at this step, requires sufficient stabilization to survive as a chemical entity under... 

Stereoselectivity. See Asymmetric induction Axial/equatorial-, Cis/trans-, Enantio-, Endo/exo- or Erythro/threo-Selectivity Inversion Retention definition (e.e.), 107 footnote Steric hindrance, overcoming of in acylations, 145 in aldol type reactions, 55-56 in corrin synthesis, 261-262 in Diels-Alder cyclizations, 86 in Michael type additions, 90 in oiefinations Barton olefination, 34-35 McMurry olefination, 41 Peterson olefination, 33 in syntheses of ce-hydrdoxy ketones, 52 Steric strain, due to bridges (Bredt s rule) effect on enolization, 276, 277, 296, 299 effect on f3-lactam stability, 311-315 —, due to crowding, release of in chlorophyll synthesis, 258-259 in metc-cyclophane rearrangement, 38, 338 in dodecahedrane synthesis, 336-337 in prismane synthesis, 330 in tetrahedrane synthesis, 330 —, due to small angles, release of, 79-80, 330-333, 337... 

A special type of interaction, the acid-base interaction, is a fairly recent discovery. It is based on the chemical concept of a Lewis acid and base, which is briefly described. The acid/base definition was proposed separately by J. N. Bronsted and G. N. Lewis. Restatement of these definitions by Lewis in 1938 led to their popularity and acceptance. The Lewis definitions are an acid is a substance which can accept an electron pair from a base a base is a substance which can donate an electron pair. By this definition, every cation is an acid in addition to chemical compounds such as BF3 and Si02. Conversely, anions and compounds like NHj, PH3, and CgHjCH2NH2 are bases. According to the acid-base theory, adhesion results from the polar attraction of Lewis acids and bases (i.e., electron-poor and electron-rich elements) at the interface. This theory is attributed to the work by Fowkes et Gutmann, and Bolger and Michaels . ... 

In his text, Shedroff adds specificity and complexity to his definition. Michael Taubitz is additionally precise in Lean, Green and Safe Integrating Safety into the Lean, Green and Sustainability Movement. He writes ... 

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