Application to Synthetic Organic Chemistry

D. J. Ramon, M. Yus, New Methodologies Based on Arene-Catalyzed Lithiation Reactions and Their Application to Synthetic Organic Chemistry, Eur. J. Org. Chem. 2000, 225-237. 

The major area of (arene)Cr(CO)3 chemistry however remains applications to synthetic organic chemistry. A study of nucleophilic and electrophilic substitution reactions of conformationally restricted (arene)Cr(CO)3 complexes has shown that nucleophiles react at carbons eclipsed by Cr-CO bonds and electrophiles at staggered postions.Both the stabilisation of a-carbocations and reactivity of a-hydrogens towards base has been investigated. The substitution of arenes with alkyllithium reagents has been studied and measurements of acidities carrried out. ... 

You have already had considerable experience with carbanionic compounds and their applications in synthetic organic chemistry The first was acetyhde ion m Chapter 9 followed m Chapter 14 by organometallic compounds—Grignard reagents for example—that act as sources of negatively polarized carbon In Chapter 18 you learned that enolate ions—reactive intermediates generated from aldehydes and ketones—are nucleophilic and that this property can be used to advantage as a method for carbon-carbon bond formation... 

Until the 1980s this technique was used mostly in mechanistic investigations to obtain information about the structure and properties of the transition state of the Diels-Alder reaction. Now, the technique is mainly used in applications of synthetic organic chemistry. 

The combination of an anionic and a pericyclic process has found broad application in synthetic organic chemistry. In these transformations, a primary addition is frequently followed by an elimination to give a reactive intermediate, which is then... 

The straightforward concept for the direct light-driven regeneration of flavin-dependent enzymes has been successfully applied for two representative classes of such enzymes a reductase and a monooxygenase. Therefore, it can be expected that this concept can also be applied to other flavin-dependent enzymes, potentially leading to additional practical catalyst systems for applications in synthetic organic chemistry. 

The nucleophilic addition of a nitroalkane to a carbonyl group, referred to as the nitroaldol or Henry reaction, is a very powerful C-C bondforming reaction of great tradition and with numerous applications in synthetic organic chemistry [36-39], Moreover, the diversity of further... 

Carbenes may be generated by many other methods for use in cyclopropanation reactions. However, relatively few of these methods are used very commonly in actual applications in synthetic organic chemistry and, therefore, the discussion that follows is limited to just these few methods. 

Despite the large utility of enamines in organic synthesis, the study of the electrochemistry of enamines and especially the application to synthetic organic reactions has been a rather minor area in electroorganic chemistry, and only a few studies have been reported. In this review these works are summarized and electrochemical synthesis and some reactions of a,/ -unsaturated urethanes (enecarbamates) are also described, since their chemical reactivity is considerably similar to that of the enamines. 

The aldol reaction is of central importance to synthetic organic chemistry in carbon skeletal elaboration. Furthermore it generates at least one and often two new stereogenic centers. Since an abundance of natural aldolases have now been identified and characterized, interest in the application of aldolases as catalysts in synthetic organic chemistry continues to increase. However, despite the potential synthetic utility of aldolase chemistry, the lyase class of enzymes is still underutilized. In contrast, the oxido-reductase and hydrolase class of enzymes have demonstrated substantial synthetic utility and are the two most utilized class of biocatalysts. 

Stimulated by the recent introduction of photochemical means to synthetic organic chemistry, the reaction and application of enamines and their derivatives have been studied (3). Although enamines have been regarded as one of the most useful synthetic weapons developed in modern organic chemistry (3), these particular groups are usually too unstable and decompose rather readily under photochemical conditions. Therefore, A-acylen-amines, which are readily prepared from imines by simple acylation, were the compounds of choice to study for photochemical reaction. 

This new experimental technique, using fluorous solvents or fluorous biphasic systems (FBS) with fluorous biphase catalysis (FBC), was developed by Vogt and Kaim [884] and by Horvath and Rabai [885] in 1991 and 1994, respectively. Since then, this method has found many applications in synthetic organic chemistry and has already been reviewed repeatedly [886-893]. Incidentally, temperature-dependent two-phase one-phase transitions are not limited to combinations of fluorous solvents with organic solvents. For example, certain mixtures of water and l-cyclohexylpyrrolidin-2-one form one phase at ambient temperature and a two-phase system at higher temperatures >ca. 50 °C), also allowing interesting separation possibilities. 

The Wittig alkenation has found widespread application in synthetic organic chemistry, and numerous papers and reviews have detailed the progress of the Wittig reaction. A principal advantage of alkene synthesis by the Wittig reaction is that the location of the double bond is absolutely fixed in contrast to the mixture often produced by alcohol dehydration. With simple substituted ylides Z-alkenes are favoured. 

Conjugate addititxis to a,p-unsaturated carbene complexes have not been extensively studied however, from the few reports that have appeared in the literature one can get a brief sense of the scope, limitations and special features of these reactions that may ultimately find application in synthetic organic chemistry. One of the earliest examples involves the addition of amines to alkynyl carbene complexes. The example in Scheme 19 is particularly interesting because complete control between 1,4- versus 1,2-addition can be exercised simply by proper choice of reaction temperature. The complex (119) suffers exclusive 1,2-addition with dimethylamine at -90 °C and exclusive 1,4-addition at -20 C. The 1,2-adduct (120) will further react with dimethylamine, but the 1,4-adduct (122) will not. This example demonstrates the importance of being attentive to reaction conditions when preparing amino carbene complexes, such as the alkynyl complex (120), or the alkenyl complex (76) in Scheme 11. 

Transition metal carbyne complexes are described by the general formula L M=CR where the carbyne ligand (=CR) is bonded to the metal by a metal-carbon triple bond. Transition metal carbene complexes have found numerous applications in synthetic organic chemistry through a variety of carbene transfer and cycloaddition reactions [17]. In contrast, carbyne (L M=CR) and vinylidene (L M=C=CRR ) complexes have far fewer applications, in part because their overall chemistry is significantly less developed [18]. Addition reactions to transition metal vinylidene complexes will be discussed in Chapter 21. The first successful synthesis of a carbyne complex was reported by Fischer and co-workers in 1973 [Eq. (8) 19]. Subsequently, many other carbyne complexes have been synthesized by the classic route of Fischer or by new synthetic methods [20]. 

Sulfides are easily oxidised at the sulfur atom by sources of electrophilic oxygen in the oxidation process, sulfur accepts electrons in its J-orbitals, leading to hypervalent sulfur compounds. The first oxidation product is the sulfoxide (23), and this is further oxidised to the stable sulfone (24) (Scheme 18) sulfones have many applications in synthetic organic chemistry (see Chapter 10, p.195). 

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