Addition cycloaddition

Transition Metal-Catalyzed Addition/Cycloaddition of Allenes 925... 

The allenes 1 directly connected with an electron-withdrawing substituent have been used successfully as synthetic building blocks for more than four decades (see Scheme 7.1). The polarization of the C=C double bonds by the acceptor substituent allows a wide and very useful range of subsequent reactions, for example nucleophilic additions, cycloadditions and miscellaneous syntheses of heterocydes. 

Keywords Aminocatalysis Conjugate addition Cycloaddition Ttninintn ion Organocatalysis... 

Apart from work of Yoshii and co-workers (62) described in Section 10.1.6 (cf. Scheme 10.19), no additional cycloaddition reactions of l,3-thiazolium-4-thiolates have been reported. 

Cyclobutanes can be conveniently prepared from cyclobutene derivatives through electrophilic addition, catalytic hydrogenation, nucleophilic addition, cycloaddition as well as light-induced addition reactions. 

The important methods involve ring closure of o-substituted anilines and phenols (type 108) and cyclization of o-unsubstituted aniline, etc., derivatives (type 109). Additionally, cycloadditions and transformations from other heterocycles are considered. Table 2 gives an overview of the important methods for preparation of derivatives of these types. 

Michael-aldol reaction as an alternative to the Morita-Baylis-Hillman reaction 14 recent results in conjugate addition of nitroalkanes to electron-poor alkenes 15 asymmetric cyclopropanation of chiral (l-phosphoryl)vinyl sulfoxides 16 synthetic methodology using tertiary phosphines as nucleophilic catalysts in combination with allenoates or 2-alkynoates 17 recent advances in the transition metal-catalysed asymmetric hydrosilylation of ketones, imines, and electrophilic C=C bonds 18 Michael additions catalysed by transition metals and lanthanide species 19 recent progress in asymmetric organocatalysis, including the aldol reaction, Mannich reaction, Michael addition, cycloadditions, allylation, epoxidation, and phase-transfer catalysis 20 and nucleophilic phosphine organocatalysis.21... 

Know the meaning of 1,2-addition, 1,4-addition, cycloaddition, diene, dienophile, polymer, monomer, polymerization. 

The conjugate addition/cycloaddition manifold is highly influenced by a number of factors, including the pyrrole complex, electrophile, solvent, temperature, and, in some cases, concentration. The key for predicting the course of the reaction between the olefin and an Ti2-pyrrole complex is the coordination site of the metal at the time of electrophilic attack (Figure 19). Although the intermediate azomethine ylide, where... 

Keywords Thiocarbonyl compounds, Thiophilic addition, Cycloaddition reactions, Enethioli-sation, Eschenmoser reaction, Sigmatropic rearrangement. 

As described here, both enantiomers of 3 can be prepared In three steps from commercially available diethyl D- and L-tartrate in up to 70% over-all yield.2 3 5 Procedures to obtain the benzylidene acetal,11 12 with the ensuing reduction step,11. 2 are based on previous literature reports. Both enantiomers of 3 have been used in highly stereoselective nitroaldol additions.3 13 Imines, nitrones, oximes, and nitrile oxides derived therefrom were recently employed in a variety of additions/cycloadditions.14 15 (-)-2-0-Benzyl-L-glyceraldehyde has further been used... 

Phosphaallenes exhibit three reactive centers, the PC double bond, the CC double bond, and the phosphorus atom. Here the PC double bond is significantly more reactive than the neighboring second double bond. The reactivity pattern is very similar to the phospha-alkenes, as far as the addition, cycloaddition, and coordination reactions are concerned. The cumulated CC double bond therefore has to be treated as an isolated group that is not greatly influenced by reactions at the PC n system. 

Organometallic complexes of Ni(0) display a rich array of reactivity both in stoichiometric reactions (e.g. oxidative additions see Oxidative Addition), cycloadditions, etc.)... 

During the past decade, many different examples of one- and two-coordinate, trivalent phosphorus compounds have been synthesized and isolated as thermally stable, but chemically reactive, products. The two-coordinate derivatives, in particular, have been found to undergo a variety of interesting and synthetically useful transformations, a few of which are illustrated below. Although several examples of addition, cycloaddition, oxidation, and metal-coordination reactions of two-coordinate phosphines are readily found in the literature (7), there is still a great deal of work to be done before the full potential of these new reagents can be realized. 

Y,R3 = CN,Ph) were applied (85S432). The addition-cycloaddition procedure [Eq. (7)] was similarly used to prepare 2(6)-amino-4//-pyrans 39b... 

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