Elimination reactions overview

Addition and elimination reactions are one of the most important classes of reactions in organic synthesis because they serve as powerful tools for the construction of a variety of organic structures. This chapter provides an overview of elimination and addition reactions using microflow reactors. 

A broad spectrum of chemical reactions can be catalyzed by enzymes Hydrolysis, esterification, isomerization, addition and elimination, alkylation and dealkylation, halogenation and dehalogenation, and oxidation and reduction. The last reactions are catalyzed by redox enzymes, which are classified as oxidoreductases and divided into four categories according to the oxidant they utilize and the reactions they catalyze 1) dehydrogenases (reductases), 2) oxidases, 3) oxygenases (mono- and dioxygenases), and 4) peroxidases. The latter enzymes have received extensive attention in the last years as bio catalysts for synthetic applications. Peroxidases catalyze the oxidation of aromatic compounds, oxidation of heteroatom compounds, epoxidation, and the enantio-selective reduction of racemic hydroperoxides. In this article, a short overview... 

Amidocarbonylation aldehydes, 11, 512 enamides, 11, 514 overview, 11, 511-555 Amido complexes with bis-Cp titanium, 4, 579 Group 4, surface chemistry on oxides, 12, 515 Group 5, surface chemistry on oxides, 12, 524 with molybdenum mono-Cp, 5, 556 with mono-Cp titanium(IV) alkane elimination, 4, 446 amine elimination, 4, 442 characteristics, 4, 413 via dehalosilylation reactions, 4, 448 HCL elimination, 4, 446 metathesis reactions, 4, 438 miscellaneous reactions, 4, 448 properties, 4, 437... 

Very different and distinct ion chemistry has been observed in the reaction between the fragment ions obtained by electron ionization of tetramethoxygermane, Ge(OMe)4, and the parent neutral81. Reactions in this system proceed by nucleophilic addition followed by elimination of formaldehyde and/or elimination of methanol. An overview of the reactions of the different ions with Ge(OMe)4 is shown in Scheme 13 for the even electron ions, and in Scheme 14 for the radical ions originating from tetramethoxygermane. In these schemes, the neutral reagent of the ion/molecule reactions, Ge(OMe)4, is not shown for the sake of simplicity but the schemes include the neutral products that are eliminated upon addition of the reagent ion to the parent neutral molecule. 

The transition metal catalyzed synthesis of arylamines by the reaction of aryl halides or tri-flates with primary or secondary amines has become a valuable synthetic tool for many applications. This process forms monoalkyl or dialkyl anilines, mixed diarylamines or mixed triarylamines, as well as N-arylimines, carbamates, hydrazones, amides, and tosylamides. The mechanism of the process involves several new organometallic reactions. For example, the C-N bond is formed by reductive elimination of amine, and the metal amido complexes that undergo reductive elimination are formed in the catalytic cycle in some cases by N-H activation. Side products are formed by / -hydrogen elimination from amides, examples of which have recently been observed directly. An overview that covers the development of synthetic methods to form arylamines by this palladium-catalyzed chemistry is presented. In addition to the synthetic information, a description of the pertinent mechanistic data on the overall catalytic cycle, on each elementary reaction that comprises the catalytic cycle, and on competing side reactions is presented. The review covers manuscripts that appeared in press before June 1, 2001. This chapter is based on a review covering the literature up to September 1, 1999. However, roughly one-hundred papers on this topic have appeared since that time, requiring an updated review. 

As indicated in the previous example, carbopalladation does not necessarily culminate in /i-hydride elimination as the expected outcome of reactions under Heck conditions. In those cases where the initial carbopalladation can be reversed at a later stage in the sequence fascinating options for catalytic processes may evolve. In particular, Catellani (for an overview see [67]) has established that norbornene, a strained olefin, which is reversibly introduced and eliminated, might efficiently serve as a relay to open new pathways for Pd-mediated processes. Indeed, most of the processes were explored and conducted both in a stoichiometric and in a catalytic fashion. 

We can modify our familiar addition and elimination surfaces to give us a combined simplified addition-elimination energy surface (Fig. 4.46). Although this system is further complicated by additional proton transfer reactions, we can get an overview of the problem space with this simplified surface as a map. The reactants are in the upper left comer. 

We are done, but let s take an overview of the process. Two addition and two elimination routes were reasonable. One acceptable reaction path is shown vertically in the center of Figure 10.4, and the alternate routes are shown to the side. 

The use of membrane reactors allows process conditions which cannot be obtained with more conventional processes (see Chapter 10 and overviews [13]) and which allow improved yields and selectivities, the use of two simultaneously occurring reactions (e.g. the main reaction and a decoking reaction to eliminate carbon deposits), controlled supply of reactant, etc. 

---