The Heck Reaction

The Heck Reaction - RX CH 3 O 2 C CH 3 O 2 C Pd(II)L 2 Br...

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Unformatted text preview: RX CH 3 O 2 C CH 3 O 2 C Pd(II)L 2 Br Ph H H H CH 3 O 2 C Pd(II)L 2 Br H Ph H H CH 3 O 2 C Ph CH 3 O 2 C CH 3 O 2 C Pd(II)L 2 + Ph H H H CH 3 O 2 C Pd(II)L 2 + H Ph H H CH 3 O 2 C Ph R' R R' Pd(II) or Pd(0) catalyst base Pd(II) K 2 CO 3 PhBr CH 3 O 2 C PhBr Ph CH 3 O 2 C HX PhBr AgCO 3 CH 3 O 2 C AgHCO 3 Pd(II) Ag + PhBr AgBr Ph CH 3 O 2 C Chem 215 The Heck Reaction Myers Reviews: Brase, S.; de Meijere, A. In Metal-catalyzed Cross-coupling Reactions , Diederich, F., and Stang, P. J., Link, J. T.; Overman, L. E. In Metal-catalyzed Cross-coupling Reactions , Diederich, F., and Intramolecular: Gibson, S. E.; Middleton, R. J. Contemp. Org. Synth. 1996 , 3 , 447471. Eds.; Wiley-VCH: New York, 1998 , pp. 99166. Eds.; Wiley-VCH: New York, 1998 , pp. 231269. Cabri, W.; Candiani, I. Acc. Chem. Res. 1995 , 28, 27. Asymmetric: Shibasaki, M.; Boden, C. D. J.; Kojima, A. Tetrahedron 1997 , 53 , 73717393. General transformation: R = alkenyl, aryl, allyl, alkynyl, benzyl R' = alkyl, alkenyl, aryl, CO 2 R, OR, SiR 3 de Meijere, A.; Meyer, F. E. Angew. Chem., Int. Ed. Engl. 1994 , 33 , 23792411. X = halide, triflate Mechanism: 2 L; 2 e Pd(0)L 2 PhPd(II)L 2 Br oxidative addition syn addition HPd(II)L 2 Br syn elimination internal rotation KHCO 3 + KBr reductive elimination Proposed mechanism involving neutral Pd: Ag + / Tl + salts irreversibly abstract a halide ion from the Pd complex formed by oxidative addition. Reductive elimination from the cationic complex is probably irreversible. Abelman, M. M.; Oh, T.; Overman, L. E. J. Org. Chem. 1987 , 52 , 41334135. 2 L; 2 e Pd(0)L 2 PhPd(II)L 2 Br oxidative addition syn addition HPd(II)L 2 + syn elimination internal rotation reductive elimination PhPd(II)L 2 + Ag + halide abstraction An example of a proposed mechanism involving cationic Pd: Pd catalyst Pd catalyst Pd(II) is reduced to the catalytically active Pd(0) in situ, typically through the oxidation of a phosphine ligand. Pd(OAc) 2 + H 2 O + nPR 3 + 2R' 3 N Pd(PR 3 ) n-1 + O=PR 3 + 2R' 3 NHOAc Ozawa, F.; Kubo, A.; Hayashi, T. Chemistry Lett. 1992 , 21772180. Andrew Haidle Belestskaya, I. P.; Cheprakov, A. V. Chem. Rev. 2000 , 100 , 30093066. Solid phase: Franzn, R. Can. J. Chem. 2000 , 78 , 957962. N S O 2 P h I N S O 2 P h P P h 3 ( 6 m o l % ) P d ( O A c ) 2 ( 3 m o l % ) D M F , 2 3 C A g 2 C O 3 , e q T i m e , h Y i e l d , % 1 1 2 4 2 4 8 5 8 3 5 5 N S O 2 P h C H 3 B y- p r o d u c t : S a k a m o t o , T . ; K o n d o , Y . ; U c h i y a m a , M . ; Y a m a n a k a , H . J . C h e m . S o c . P e r k i n T r a n s . 1 1 9 9 3 , 1 9 4 1 1 9 4 2 ....
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The Heck Reaction - RX CH 3 O 2 C CH 3 O 2 C Pd(II)L 2 Br...

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