Copper amides bonding

Note The silver (I) carbene complex features Ag-N amide bonds in a five-membered met-allacycle with Ag-Ag bonds, but the copper(II) complex has Cu-0 imino oxide bonds in a... 

Phenylalanylglycine amide was found to undergo ring closure to form 3-benzyl-2,5-diketopiperazine in the absence of metal ions (reaction XLI). In the presence of copper(II) at pH 5, the protonated form of the amide underwent hydrolysis reactions at both the peptide and amide bonds. 

Silver and copper amides as the simplest acid/base catalysts for stereoselective carbon—carbon bond-forming reactions, particularly [3+2] cycloaddition reactions 13CEJ9420. 

All this applies in particular to the copper (l)-catalyzed coupling of azides and terminal acetylenes to form exclusively 1,4-disubstituted 1,3-triazole linkages, according to example (b) in Scheme 15.1. From the biological standpoint, the topological and electronic features shared by 1,2,3-triazoles and amide bonds are particularly important, since the latter are ubiquitous connectors in Natiue. From the synthetic point of view, it is important to note that alkyl azoles can give 1,4- and 1,5-disubstituted, or syn- and anti-1,2,3-triazoles (Scheme 15.2). 

When the reaction is carried out with (BuOCu, in the absence of a lithium salt, yields and enantioselectivities are not affected. This indicates that the diamine coordinates to the copper atom at the enantio-differentiating step, even in the presence of the cationic lithium atom. In addition, ESl-MS experiments support the presence of complex O (Scheme 70). Shibasaki et al. have proposed a working hypothesis for the catalytic cycle, as shown in Scheme 70. Copper amide P is generated from O and (BuOLi, and next, the copper-nitrogen bond cleaves... 

Copper complexes of bis(2,2 -dipyridyl)dithiocarbamate have been prepared upon insertion of carbon disulfide into the copper-nitrogen bonds of the corresponding 2,2 -dipyridylamine (dpa) complexes (195, 196). Kumar and Tuck (195) initially noted this behavior for [Cu(dpa)] , [Cu(dpa)2], and [Cu(dpa)(dppe)l [dppe = l,2-bis(diphenylphosphino)ethane], but characterization was made only on the basis of the presence of characteristic v(C—S) and v(C—N) bands in their IR spectra. Later, this was confirmed by the X-ray crystal structure of [Cu(S2Cdpa)2], formed upon slow evaporation of a carbon disulfide solution of [Cu(dpa)2] (Eq. 21) (196). The transformation is actually quite complex as in the dpa complex, metal coordination is through the nitrogen atoms of the pyridyl rings (197), and thus a rearrangement to the amide form must occur prior to carbon disulfide insertion. 

Synthesis of benzoxazines through aziridine ring opening followed by intramolecular C—N bond formation was reported by Sekar and co-workers. " In this approach, a domino ring opening of A -Ts aziridines 332 with o-iodo-phenols 333 followed by copper-catalyzed intramolecular C(aryl)-N(amide) bond formation in the presence of ethyl-enediamine ligand has been established to afford the resultant product 334 in excellent yield (Scheme 40.73). The trans selectivity was confirmed by H NMR spectroscopy and single crystal X-ray analysis. 

The above-described structures are the main representatives of the family of nitrogen ligands, which cover a wide spectrum of activity and efficiency for catalytic C - C bond formations. To a lesser extent, amines or imines, associated with copper salts, and metalloporphyrins led to good catalysts for cyclo-propanation. Interestingly, sulfinylimine ligands, with the chirality provided solely by the sulfoxide moieties, have been also used as copper-chelates for the asymmetric Diels-Alder reaction. Amide derivatives (or pyridylamides) also proved their efficiency for the Tsuji-Trost reaction. 

Parco et al. described a copper-catalyzed amidation of vinyl iodide 115 to give 116 (Scheme 20).28e Enhanced conversions were attained using copper(i) thiophenecarboxylate (GuTG) in a polar aprotic solvent such as NMP. The total synthesis of the antitumor natural product, lobatamide G, has been accomplished by using this reaction.28f Buchwald et al. developed a general and efficient copper-catalyzed method using N,N -dimethyl ethylenediamine L8. The double-bond geometry of the alkenyl halides was retained under the reaction conditions. 

Hosokawa, Murahashi, and coworkers demonstrated the ability of Pd" to catalyze the oxidative conjugate addition of amide and carbamate nucleophiles to electron-deficient alkenes (Eq. 42) [177]. Approximately 10 years later, Stahl and coworkers discovered that Pd-catalyzed oxidative amination of styrene proceeds with either Markovnikov or anti-Markovnikov regioselectivity. The preferred isomer is dictated by the presence or absence of a Bronsted base (e.g., triethylamine or acetate), respectively (Scheme 12) [178,179]. Both of these reaction classes employ O2 as the stoichiometric oxidant, but optimal conditions include a copper cocatalyst. More recently, Stahl and coworkers found that the oxidative amination of unactivated alkyl olefins proceeds most effectively in the absence of a copper cocatalyst (Eq. 43) [180]. In the presence of 5mol% CUCI2, significant alkene amination is observed, but the product consists of a complicated isomeric mixture arising from migration of the double bond into thermodynamically more stable internal positions. 

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