C—B cross-coupling

The use of other transition metals Ni and Cu has been demonstrated for C—B bond formation. Percec and coworkers first reported NiCl2(dppp)-dppp for boiylation of aryl bromide with neopen-tylglycolborane [266]. Mixed ligand system NiClj(dppp)-dppf efficiently catalyzed the coupling of 

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Scheme 10.2 On-column synthesis of Fc-labeled ODNs (see Ref. 21. (a) ODN synthesis, (b) Cross-coupling reaction conditions Pd(PPh3)4, Cul, TEA (triethanolamine), DMF (dimethylformamide), and (c) Fc-ODN deprotection. Analogous procedure is used for...

Bhong, B. Y., Shelke, A. V., and Karade, N. N. 2013. Nano copper oxide mediated Ugand-free C-S cross-coupling and concomitant oxidative aromatization of 4-aryl-3,4-dihydropy-rimidin-2(l//)-thione with diaryUodonium salts. Tetrahedron Lett. 54(8) 739-743. 

Scheme 2 Cross-coupling reactions (a) traditional cross-coupling, (b) C-H activation, (c) oxidative cross-coupling...

Breitler S, Oldenhuis NJ, Fors BP, Buchwald SL (2011) Synthesis of unsymmetrical diarylureas via Pd-catalyzed C-N cross-coupling reactions. Org Lett 13(12) 3262-3265 Hooker JM, Reibel AT, Hill SM, Schueller MJ, Fowler JS (2009) One-Pot, Direct Incorporation of [ C]C02 into Carbamates. Angew Chem Int Ed 48(I9) 3482-3485 Peterson SL, Stucka SM, Dinsmore CJ (2010) Parallel synthesis of ureas and carbamates from amines and CO2 under mild conditions. Org Lett 12(6) 1340-1343 Wei Y, Liu J, Lin S, Ding H, Liang F, Zhao B (2010) Acetoacetanilides as masked isocyanates facile and efficient synthesis of unsymmetrically substituted ureas. Org Lett 12 (19) 4220 223... 

The postulated steps that constitute the Suzuki coupling process are shown in Scheme 25. After oxidative addition of the organic halide to the palladium(o) catalyst, it is presumed that a metathetical displacement of the halide substituent in the palladium(ii) complex A by ethoxide ion (or hydroxide ion) takes place to give an alkoxo-palladium(ff) complex B. The latter complex then reacts with the alkenylborane, generating the diorganopalladium complex C. Finally, reductive elimination of C furnishes the cross-coupling product (D) and regenerates the palladium(o) catalyst. 

For overviews of applications of the Heck reaction in natural products synthesis, see (a) Link, J. T. Overman, L. E. In Metal-Catalyzed Cross-Coupling Reactions, Diederich, F., Stang, P. J., Eds. Wiley-VCH New York, 1998 Chapter 6. (b) Brase, S. de Meijere, A. In Metal-Catalyzed Cross-Coupling Reactions Diederich, F., Stang, P. J., Eds. Wiley New York, 1998 Chapter 3.6. (c) Nicolaou, K. C. Sorensen, E. J. Classics in Total Synthesis VCH New York, 1996 Chapter 31. These authors refer to the Heck reaction as "one of the true "power tools" of contemporary organic synthesis" (p. 566). 

The HMQC spectrum of podophyllotoxin shows heteronuclear crosspeaks for all 13 protonated carbons. Each cross-peak represents a one-bond correlation between the C nucleus and the attached proton. It also allows us to identify the pairs of geminally coupled protons, since both protons display cross-peaks with the same carbon. For instance, peaks A and B represent the one-bond correlations between protons at 8 4.10 and 4.50 with the carbon at 8 71.0 and thus represent a methylene group (C-15). Cross-peak D is due to the heteronuclear correlation between the C-4 proton at 8 4.70 and the carbon at 8 72.0, assignable to the oxygen-bearing benzylic C-4. Heteronuclear shift correlations between the aromatic protons and carbons are easily distinguishable as cross-peaks J-L, while I represents C/H interactions between the methylenedioxy protons (8 5.90) and the carbon at 8 101.5. The C-NMR and H-NMR chemical shift assignments based on the HMQC cross-peaks are summarized on the structure. 

Transition metal catalysed cross-coupling reactions of organometalUc reagents containing Zn, Si, Mg, Sn or B with organic electrophiles in the presence of group 8-10 metals, notably Ni and Pd, are routinely the method of choice, both in academia and industry, for the preparation of C-0, C-S, C-H, C-N and C-C bonds [1]. 

Metal complexes as catalysts for oxygen, nitrogen and carbon-atom transfer reactions (Tsutomu Katsuki) Metal complexes as catalysts for H-X (X = B,CN, Si, N, P) addition to CC multiple bonds (M. Whittlesey) Metal complexes as catalysts for C-C cross-coupling reactions (I. Beletskaya, A.V. Cheprakov)... 

Louie J, Hartwig JF (1996) A route to PdO from Pdll metallacycles in amination and cross-coupling chemistry. Angew Chem Int Ed Engl 35 2359-2361 Mucalo MR, Coouey RP (1989) F.T.I.R. spectra of carbon monoxide adsorbed on platinum sols. J Chem Soc Chem Commun 94—95 Munoz MP, Martin-Matute B, Fernandez-Rivas C, Cardenas DJ, Echavarren AM (2001) Palladacycles as precatalysts in Heck and cross-coupling reactions. Adv Synth Catal 343 338-342... 

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