Copper catalysis addition

Although the resulting vinylallenes 48 were usually obtained as mixtures of the E and Z isomers, complete stereoselection with regard to the vinylic double bond was achieved in some cases. In addition to enyne acetates, the corresponding oxiranes (e.g. 49) also participate in the 1,5-substitution (Scheme 2.18) and are transformed into synthetically interesting hydroxy-substituted vinylallenes (e.g. 50) [42], Moreover, these transformations can also be conducted under copper catalysis by simultaneous addition of the organolithium compound and the substrate to catalytic amounts of the cuprate (see Section 3.2.3). 

The conjugate addition of organometallic reagents R M to an electron-deficient alkene under, for instance, copper catalysis conditions results in a stabilized car-banion that, upon protonation, affords the chiral yS-substituted product (Scheme 7.1, path a). Quenching of the anionic intermediate with an electrophile creates a disubstituted product with two new stereocenters (Scheme 1, path b). With a pro-chiral electrophile, such as an aldehyde, three new stereocenters can be formed in a tandem 1,4-addition-aldol process (Scheme 1, path c). 

The Michael additions of various carbon nucleophiles such as cyanide [15b, 22b], anions generated from nitromethane [27], ferf-butyl acetate [9], malon-ates [27] and O Donnell s glycine equivalent [541, cuprates [9,15b] or Grignard reagents [53] under copper catalysis [55] have also been reported (Scheme 24). 

Unactivated aUsynes 209 undergo the addition of aryhnagnesium reagents under cooperative iron and copper catalysis, yielding trisubstituted alkenyhnagnesium species. They can be trapped with electrophiles, giving tetrasubstituted alkenes such as 210. In some... 

For the aziridination of 1,3-dienes, copper catalysis gave better yields of A-tosyl-2-alkenyl aziridines with 1,3-cyclooctadiene, 1,4-addition occurred exclusively (50%) [46]. Good results were also obtained on rhodium catalysed decomposition of PhI=NNs (Ns = p-nitrophenylsulphonyl) with some alkenes the aziridination was stereospecific, whereas with chiral catalysts asymmetric induction (up to 73% ee) was achieved. However, cyclohexene gave predominantly (70%) a product derived from nitrene insertion into an allylic carbon-hydrogen bond [47]. 

Although in some cases, copper catalysis has little effect on the stereochemistry, some asymmetric induction by chiral copper catalysts such as copper(i) complexes of aminotropone iminates (8) [79] or the chiral arylthiocopper compound (9) [80] has been achieved. Chiral zinc(n) complexes (8) also promote enantioselective conjugate addition [81]. 

Tlie latter reagent undergoes 1,2-addition to a,p-unsaturated aldehydes 1,4-addition, with copper catalysis, is observed with cyclohexenone alone. A more satisfactory reagent for the conjugate introduction of the hydroxymethyl group is the allyldimethylsilylmethyl Grignt reagent... 

The mechanism of copper catalysis is obviously related to the halogcnaiing properties of the copper salts the activity is restricted to the halides, CuCN, CuOAc, CufOjSCFa) and CuF being inactive. The addition of halide ions, BrCN or croiyl bromide to CuCN, however, restores an activity comparable to CuBi efficiency. Crotyl bromide is a particularly efficient additive and may be an intermediate in the process. The rate increases by a factor of three in relation to the neat CuBr catalyzed reaction. Yields Itigher than 90% can thus be obtained. Similarly. UBr reactivates the catalyst 16). 

Copper(I) halides have been shown previously to accelerate the formation of (Z)-3-iodoprop-2-enoic acid. ,8,9,io xhe formation of the (E)-isomer during these low temperature investigations indicated that, at higher temperature, copper catalysis could accelerate the formation of the thermodynamically favored (E)-isomer. Therefore, we decided to investigate the effect of temperature on the copper-catalyzed addition of HI to propiolic acid, with a view to creating a copper-catalyzed, one-step synthesis of the (E)-isomer. 

The iodine-zinc exchange of an alkyl iodide with EtjZn is proi oted by the addition of small amounts of copper(I) salts such as CuCN or Cul. Although the exact reason for this copper catalysis is now known, it has been speculated that the presence of copper(I) salts promotes a radical chain-reaction resulting in the formation of a dialkylzinc species (Scheme 9-32) [22b]. Similarly, the addition of other transition metals such as nickel and palladium salts promotes radical reactions. 

Although 1,2-addition of Grignard reagent to N-alkyl-N-silylformamide aflforded the same type of product, imines, in the presence or absence of a copper salt, N-phenyl-N-silylformamide afforded a doubly alkylated amine in the reaction of Grignard reagent under copper catalysis [Eq. (73) 152]. 

The 1,4-addition of Grignard reagents under copper catalysis, followed by a trap of the resulting (magnesium) enolates with an appropriate electrophile, is a versatile method for double functionalization or double carbon-carbon bond formation at the a- and / -positions of an olefinic bond that bears a carbonyl group [Eq. (89)]. Recently, this topic has been extensively reviewed [155]. Examples [170,173,174] of this notion are presented in Eqs. (77), (90) [170], and (91) [174]. 

Metal Effects and Prooxidant Action. Ascorbic acid is prooxidant in some situations. Kanner et al. (28) showed that Cu increased the oxidation of linoleate using loss of 8-carotene as an indicator. However, when sufficient ascorbic acid was added to his system, copper catalysis was reversed. Furthermore, when Fe was added, the addition of ascorbic acid increased the prooxidant effect. Previous publications (29) have discussed the deactivation of copper catalysis by ascorbic acid, but in iron-catalyzed oxidation, Fe " initiates oxidation of lipid (2). Fe is formed from Fe by ascorbic acid. Many foods contain metals, and the... 

Severe limitations on the usefulness of the classical Wurtz reaction in the production of cross-coupled products have led to the development of many more generally useful variants. In particular, the use of copper catalysis and of stoichiometric organocuprate species have proved very valuable. The reactions of ir-allylnickel halides with sp halides is also represented by equation (1), and the uses of these reagents are treated separately. In order to provide a balanced view of the value of ir-allylnickel halides, some additional reactions with centers other than sp are described. 

By derivatizing an a,p-unsaturated acid into the mono ester of chiral 1,1 -bi-8,8 -naphthol the reaction with lithium dialkylcuprates leads to saturated ketones containing chirality centers at the p-carbon atoms." Consecutive 1,4-addition and 1,2-addition account for this result. The alkyl transfer to enones from Grignard reagents under copper catalysis is subject to chiral modification, e.g., by the introduction of 56" or 57." ... 

Copper catalysis for particulate removal from diesel exhaust gas. Copper fuel additives in combination with copper coatings. 

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