Conjugate metal-catalyzed reactions

Polyfluorenes synthesized by Fukuda et al. have relatively local molecular weights and some degree of branching and nonconjugated linkages via conjugation at carbon atoms at positions other than 2 and 7.11 Inbasekaran and co-workers chose to minimize such effects by using transition-metal-catalyzed reactions of... 

The resulting magnesium species can be used in transition metal-catalyzed reactions. In the presence of a catalytic amount of a copper(I) salt and chlorotri-mefhylsilane, conjugate addition to a variety of enones occurs (Scheme 3.99) [122]. 

Many other examples of transition metal catalyzed reactions such as oxidation, dimerization or telomerization of conjugated diene have been performed in these borderline anions-based ionic liquids and are described in recent reviews [4]. 

Metal-catalyzed reactions have been of major importance in synthetic organic chemistry. Over the past decade, enantio- and diastereoselective metal-mediated domino catalysis has emerged as an effective tool to construct really highly complex molecules in one-pot processes [2, 4b,d]. Among them, enantioseletcive metal-catalyzed conjugate additions (in particular, Cu-catalyzed 1,4-addition to a,P-unsaturated carbonyl compounds) have been useful components of domino reactions [4d, 5]. The generated metal enolates 2 after the additions of nucleophiles readily react with a variety of electrophiles (Scheme 11.1). Enantioselectivity of 3 depends on the first addition of nucleophiles to the P-position of the unsaturated carbonyl compounds 1. 

Catalytic nucleophilic substitution reactions comprise some of the most commonly used catalytic processes in S)mthetic organic chemistry. Substitutions at aromatic and vinylic halides and sulfonates, sho vn generically in Equation 19.1, are commonplace in the preparation of pharmaceutical candidates, have often been used in the s)mtheses of natural products, and have been used many times in the syntheses of sophisticated conjugated organic materials. These metal-catalyzed reactions are typically called cross-coupling reactions. ... 

Transition metal catalyzed reactions and in particular cross-couplings are commonly employed to access conjugated dienes. Recently, efforts have been devoted to the stereoselective synthesis of silylated, stannylated, or nitrogenated 1,3-dienes using such methods. 

Metal-Catalyzed Reactions The metal-catalyzed bisthiolations are currently limited to Pd, Ni, and Rh complexes, where the stereoselective formation of alkenes 40 with high (Z)-selectivity was observed. For the Ni-catalyzed reaction, it is possible to prepare stereo-chemically defined 1,4-bisthio substituted conjugate dienes 41 through sequential alkyne insertions to Ni—S and Ni—C bonds 42 (Scheme 46.7). The use of silyldisulfides" followed by one-pot desilyation and electrophilic addition... 

Gothelf presents in Chapter 6 a comprehensive review of metal-catalyzed 1,3-di-polar cycloaddition reactions, with the focus on the properties of different chiral Lewis-acid complexes. The general properties of a chiral aqua complex are presented in the next chapter by Kanamasa, who focuses on 1,3-dipolar cycloaddition reactions of nitrones, nitronates, and diazo compounds. The use of this complex as a highly efficient catalyst for carbo-Diels-Alder reactions and conjugate additions is also described. 

The cycloaddition reactions of carbonyl compounds with conjugated dienes cannot be discussed in this context without trying to understand the reaction mechanistically. This chapter will give the basic background to the reactions whereas Chapter 8 dealing with theoretical aspects of metal-catalyzed cycloaddition reactions will give a more detailed description of this class of reactions, and others discussed in this book. 

Although the path (a) has been verified by a stoichiometric reaction [23], the details of exact reaction mechanism remain unsettled. Triggered by this publication [and the Pd-catalyzed doublethiolation of alkynes described in Eq. (7.7) in Section 7-3], a number of transition metal-catalyzed additions of S-X or Se-X bonds to C-C unsaturated organic compounds started to be published. In 1994, BackvaU et al. applied the Pd(OAc)2-catalyzed hydrothiolation to conjugated enynes and obtained 17,... 

After the initial two reports of Rh- and Co-catalyzed reductive aldol couplings, further studies did not appear in the literature until the late 1990s. Beyond 1998, several stereoselective and enantioselective reductive aldol reactions were developed, which are catalyzed by a remarkably diverse range of metal complexes, including those based upon Pd, Cu, Ir, and In. In this chapter, transition metal-catalyzed aldol, Michael, and Mannich reactions that proceed via transition metal hydride-promoted conjugate reduction are reviewed. 

Purify the reduced IgG from excess 2-mercaptoethylamine and reaction by-products by dialysis or gel filtration using a desalting resin. All buffers should contain 1-10 mM EDTA to preserve the free sulfhydryls from metal-catalyzed oxidation. The sulfhydryl-containing half antibody now may be used in conjugation protocols that use —SH-reactive heterobifunctional crosslinkers (Chapter 5, Section 1). 

Add at least 5 mg/ml of a sulfhydryl-containing protein or other molecule to the SPDP-modified vesicles to effect the conjugation reaction. Molecules lacking available sulf-hydryl groups may be modified to contain them by a number of methods (Chapter 1, Section 4.1). The conjugation reaction should be done in the presence of at least lOmM EDTA to prevent metal-catalyzed sulfhydryl oxidation. 

After that, studies on the palladium-catalyzed reactions of conjugated dienes attracted little attention. They have only been reexamined since the late 1960 s. The scope of the reaction of butadiene catalyzed by palladium complexes has gradually been established. The catalysis by palladium is different from those of other transition metals. Although palladium is located below nickel in the periodic table, the catalytic... 

Several examples are known of the transition metal-catalyzed synthesis of 1,2,3-buta-trienes, which possess one more cumulated C=C double bond than allenes. Most of the reported examples of the butatriene synthesis involve dimerization of terminal alkynes and conjugated enynes are typical side products of the reactions. 

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