Cu-catalyzed and promoted

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. 

The first metal-catalyzed nitrogen atom-transfer process was reported by Kwart and Khan, who demonstrated that copper powder promoted the decomposition of benzenesulfonyl azide when heated in cyclohexene.280 Evans has demonstrated that Cu(i) and Cu(n) triflate and perchlorate salts are efficient catalysts for the aziridination of olefins employing TsN=IPh as the nitrene precursor.281 Subsequent to this finding, intensive effort has focused on the identification of... 

An initial stndy demonstrated that Josiphos and its inverted analogue 11 were very effective in promoting the Cu-catalyzed conjugate addition of EtMgBr to unsaturated crotonates (Scheme 5). It is noteworthy that the use of sterically hindered esters, which nsnally helps to avoid nndesired 1,2-additions, or alternatives for esters such as an oxa-zolidinone, are not reqnired. Indeed, the highest conversions and stereoselectivities are obtained with methyl crotonate. ... 

A Ru complex with a chiral oxazolinylferrocenylphosphine (S)-6 (substrate Ru=100 l) with Cu(0S02CF3)2 promoted hydrosilylation of acetophenone using diphenylsilane (2 equivalents) in ether at 0 °C to give (R)-l-phenylethanol in 95% ee and in 59% yield after hydrolysis (Scheme 16) [31]. Propiophenone was reduced with 97% optical yield. This complex was also effective for the hydrosilylation of 2-phenyl-l-pyrroline in toluene at 0 °C to afford the S chiral amine in 88% ee [31].RuCl2[(.R)-TolBINAP][(S)-7] and Ag0S02CF3 catalyzed the hydrosilylation of acetophenone (substrate Ru Ag=100 l 4) with diphenylsilane to give the R product in 82% ee [32,33]. 

N-Arylaminophthalimides, hydrazines, hydrazones, and N-H containing heterocycles are N-arylated by combined use of Ar3Bi and Cu(OAc)2 (Scheme 14.134) [281] in which Cu(OAc)2 oxidizes Ar.l i to Ar jl i(OAc)2 and catalyzes the arylation via transmetalation (Section 14.3.4.2). The Cu(OAc)2-promoted N-arylation of amides, sulfonamides, ureas, carbamates, and anilines with ArsBi proceeds efficiently in the presence of EtsN or pyridine (Scheme 14.135) [282]. N-Arylation occurs selectively on the primary amino group of aminobenzanilides (Scheme 14.136) [283]. A variety of amines are N-alkylated in moderate yields by use of alkylbismuthanes assisted by Cu(OAc)2 [284]. 

That the TC group is positioned near the CD moiety in 42 was confirmed by measuring kinetics of deacylation of 43 promoted by 42 [M Cu(II), Ni(II), Cu(II)] and the analogue of 42 prepared by random functionalization. Kinetics of reactions catalyzed by the PEI derivatives followed the Michaelis-Menten scheme. Parameter MK is close to the formation constant for the most stable complex formed between the polymer and 43. For the PEI derivative prepared by site-directed functionalization, 1/AT was (3.7-6.4) x 10 M at 25 °C, being 5.8-S.7 times greater than those for the analogue prepared by random functionalization. This indicates that an extra binding force is present in the complex formed between 43... 

Reduction of extracellular substrates can also occur at the expense of reduced moieties on the cell surface (Fig. 2.5). These reactions may occur in the dark or require promotion by light. They are nonenzymatic, and the reductant must be regenerated while it is consumed in order to continue catalyzing the reaction. Examples of this reaction are Cu(II) and Fe(III) reduction by algal cell walls (Anderson and Morel, 1980 Jones et al., 1987). 

Cu-promoted reaction and Cu-catalyzed C-H amination merit some analysis of the former process. From the standpoint of reaction utility, the work of Dauban and Dodd [31, 32] and, more recently, Lebel [33] has advanced Cu-catalyzed alkene aziridination to a state-of-the-art synthetic method. In particular, Dauban and Dodd have shown that pre-formation of sulfonyliodoimines is not required and that such species can be generated in situ from the corresponding sulfonamide and Phl=0. These conditions greatly expand the number and type of sulfonamide derivatives that will engage in olefin aziridination processes. 

Ni(II), Cu(II), and Zn(ll) were bound to this system. The catalytic oxidation of 2,6-dimethylphenol in air is catalyzed by the Co(II) complex. The reactivity of the catalyst is reduced from that of the homogeneous analog. Some variation in product distribution (benzoqulnone vs. dimer) is observed with changes in loading. Benzoquinone is formed by a second oxidation of the phenoxy radical and is thus promoted by a higher concentration (load) of Co(II). 

Aryl and alkyl-substituted diynes and tetraynes have been synthesized in good yields (82-99%) by TBAF-promoted desily-lation and Cu-catalyzed oxidative dimerization of triisopropylsi-lyl (TlPS)-protected acetylenes (eq 38). Copper acetate was used as oxidant in this reaction. Aryl- and alkenyl alkynes were made under similar conditions (eq 39). Pd/C with TBAF was used in ligand- and copper-free, one-pot, domino Halex-Sono-gashira reactions. Similarly, TBAF promoted the synthesis of 2-substituted indoles by a tandem Sonogashira/cyclization reaction of 2-iodoanilines and terminal alkynes. ... 

Arylation of active methylene compounds has been carried out using Cu salts as promoters under severe conditions [2], Recently it was discovered that the reaction can be carried out much more smoothly using Pd catalysts. The first Pd-catalyzed intermolecular arylation of cyanoacetate and malononitrile with aryl iodides was carried out by Takahashi using PPhs as a ligand, and was applied to a simple synthesis of tetracyanoquinodimethane (2) by the reaction of p-diiodobenzene with malononitrile [3], The intramolecular arylation of malonates and -diketones with aryl iodides proceeds smoothly. Presence of a cyano group seemed to be important [4,5], The arylation has been successfully extended to halides of heterocycles, such as pyridine, quinoline and isoquinoline. The reaction of bromoxazole 3 with sulfone 4 is an example [6]. 

Shamim and Paul (2010) found that the silica modified by a Schiff base-type ligand promoted the Cu-catalyzed, three-component synthesis of 1,2,3-triazoles in water at room temperature (Scheme 4.3). It also exhibited higher efficiency than Wang s promoter, probably because the Schiff bases possess much better coordinating ability than the primary amines. 

From the mechanistic viewpoint, there are numerous reported examples of base (nucleophile)-catalyzed addition, simultaneously promoted by electrophilic metal ions. A typical example of nucleophilic-electrophilic catalysis is provided by the addition of hydrochlorosilanes to alkenes, which occurs in the presence of Cu(II) and/or Cu(I) salts, and tertiary amines (3), such as CU2O-tetramethylethylenediamine system (134) catalyzes exclusively j8-hydrosilylation of acrylates. 

The synthesis of benzofurans and related compounds from ortho-iodophenol and copper] I) acetylides via a coupling-cydization reaction (vide infra) was introduced by Castro in the 1960s [75-77] and stimulated the development of many contemporary transition metal-catalyzed synthetic approaches toward the assembly of the benzofuran unit. In a subsequent report from Castro s group, it was proposed that the formation of the benzofuran core occurs in a stepwise fashion with the intermediacy of ortho-alkynylphenol, which, upon activation by the Cu(I) salt promoter, undergoes subsequent cydoisomerization [77]. 

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