Addition reactions Diels-Alder reaction

Rearrangement reaction Addition reaction Diels-Alder reaction Claisen reaction Substitution reaction Elimination reaction Wittig reaction Grignard reaction... 

This kind of heterobimetallic complexes are excellent catalysts for a wide range of reactions, including epoxidation of enones, hydrophosphonylation of imines and aldehydes, and a range of asymmetric C-C bond formation reactions, involving Michael addition reaction, Diels-Alder reaction, aldol and nitroaldol reaction, etc. The alkaU metal has a profoimd effect on the catalytic property of these compounds. 

From the foregoing it can be seen that the nitro group can be activated for C-C bond formation in various ways. Classically the nitro group facilitates the Henry reaction, Michael addition, and Diels-Alder reaction. Komblum and Russell have introduced a new substitution reaction, which proceeds via a one electron-transfer process The Spj l reactions have... 

The conversion of primary or secondary nitro compounds into aldehydes or ketones is normally accomplished by use of the Nef reaction, which is one of the most important transformations of nitro compounds. Various methods have been introduced forthis transformation (1) treatment of nitronates with acid, (2) oxidation of nitronates, and (3) reduction of nitroalkenes. Although a comprehensive review is available,3 important procedures and improved methods published after this review are presented in this chapter. The Nef reaction after the nitro-aldol (Henry reaction), Michael addition, or Diels-Alder reaction using nitroalkanes or nitroalkenes has been used extensively in organic synthesis of various substrates, including complicated natural products. Some of them are presented in this chapter other examples are presented in the chapters discussing the Henry reaction (Chapter 3), Michael addition (Chapter 4), and Diels-Alder reaction (Chapter 8). 

In addition, the Diels-Alder reaction was found to be catalyzed by salt 18 giving the e d(( -product in 97% yield in 1 h. Apphcation of Me3SiOTf resulted in no product formation, while MejSiNTfj and Et3SiNTf2 gave a yield of 6 and 13%, respectively (Scheme 12). Both reactions proceeded in the same way in the presence of the proton scavenger 2,6-di-fe/t-butylpyridine with salt 18, which should rule out a proton promoted reaction. 

Cycloadditions, Carbene Additions and Diels-Alder Reactions... 

The oxazoline ring acts as an electron-withdrawing group for a substituent at the 2-position. Thus, the ot-protons of a 2-alkyloxazoline exhibit some acidity and can be abstracted by a base. A 2-alkenyloxazoline can be viewed as a masked acrylic acid derivative and is capable of undergoing Michael addition and Diels-Alder reactions. These reactions can often be carried out stereoselectively using a chiral oxazoline. Other types of chiral auxilliaries, most notably oxazolidinones, are also very effective for these types of applications. However, they are outside the scope of this chapter. The discussion in this section will focus on the new developments with oxazolines. 

Cado, R, Jacquault, P, Dozias, M.J., Bazureau, J.P., and Hamelin, J. 1997. Tandem conjugate carbon addition-intermolecularhetero Diels-Alder reactions using ethyl IH-perimidine-2-acetate as a ketene aminal with heating or microwave activation. Journal of Chemical Research, 176-77. 

Decarboxylation may also be required in cases other than those involving derivatives of acetoacetic or malonic esters. The usefulness of this operation stems from the tremendous synthetic potential of carboxylic acids and their derivatives as substrates employed in C-C bond-forming reactions such as a-alkylation, Michael addition, the Diels-Alder reaction, etc. As the immediate result of these reactions, acid derivatives containing diverse structural backbones are formed. Hence the scope of these methods in synthetic practice depends heavily upon the opportunity to remove the carboxyl group after it has... 

Other Uses. Reagent 1 has been used for enantioselec-tive enolborination, albeit with poor (1.1 1) selectivity. Similar bis-sulfonamide-derived boron Lewis acids have been used for aldol additions, "" ester-Mannich reactions, Diels-Alder reactions, Ireland-Claisen reactions, and [2,3]-Wittig rearrangements. Similar bis-sulfonamide-derived aluminum Lewis acids have been used for aldol additions, Ehels-Alder... 

Essentially, a suprafacial-suprafacial or an antarafacial-antarafacial cycloaddition is equivalent to a concerted syn addition. A suprafacial-antarafacial or an antarafacial-suprafacial process is equivalent to a concerted anti addition. The Diels-Alder reaction is suprafacial for both components, so that the stereochemical relationships among the substituents are maintained in the product. In Example 6.6, suprafacial addition to the dienophile component means that the two carbomethoxy groups that are cis in the starting material also are cis in the product. Suprafacial reaction at the diene component leads to a cis orientation of the two methyl groups in the product. 

A multipurpose template is the oxazolidinone 19 which is endo-fused to a norbomane skeleton. Proper A-acyl derivatives are useful for asymmetric alkylation, conjugate addition, and Diels-Alder reactions. 

Asymmetric aldol, conjugate addition, and Diels-Alder reactions compared... 

Since conjugate (Michael) addition and Diels-Alder reactions use a,p-unsat united carbonyl compounds, asymmetric versions of these reactions could use the auxiliaries that we have seen in aldol reactions in the form of 118 and 119. Diels-Alder reactions work very well with these unsaturated amides and also with amides 121 derived from Oppolzer s chiral sultam14 120, prepared simply from camphorsulfonyl chloride. 

A few additional imino Diels-Alder reactions have been reported which involve iminium salts. Bohme and Ahrens found that the perchlorate salt in Eq. (11)... 

In addition, the Diels-Alder reactions of oxazoles 3 bearing alkoxy substituents at the 5 position were disclosed by Kondrat eva and Huang in 1961 (Fig. 3.2). In contrast to the alkyloxazoles, the cycloadditions of derivatives such as maleimide with 3 resulted in the formation of pyridinols 4 rather than the expected 3 - alkoxypyridines. 

DMAP has been incorporated into dispirooxindole-fused heterocycles via a domino 1,4-dipolar addition and Diels-Alder reaction of DMAP, acetylenedicarboxylates, and 3-phenacylideneoxindoles. The reactive intermediate is an in situ generated Huisgen 1,4-dipole. 

In connection with cycloaddition reactions it is convenient to mention yet another interesting possibility of the exploitation of the Fukui s approach. This possibility concerns the rationalization of the so-called endo addition in Diels-Alder reactions. In order to demonstrate the preference of this specific reaction mode let us assume a simple addition of two butadiene molecules resulting in the formation of vinylcyclohexene. For this reaction there are two alternative 4s + 2s reaction paths differing in the stereochemical arrangement of the corresponding products. One of these products is of the so-called exo type, whereas for the other the name endo is reserved. 

ABSTRACT. Aldehydes, ketones and a,p-unsaturated aldehydes and ketones undergo a wide variety of reactions with unactivated alkenes in the presence of alkylaluminum halide catalysts. Ene reactions, Diels-Alder reactions, Prins reactions and cation-olefin addition reactions occur depending on the choice of substrate and Lewis acid. 

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