The Heck Reaction

The Heck Reaction - R–X CH 3 O 2 C CH 3 O 2 C Pd(II)L 2...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: R–X 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 Ph–Br CH 3 O 2 C Ph–Br Ph CH 3 O 2 C HX Ph–Br AgCO 3 – CH 3 O 2 C AgHCO 3 Pd(II) Ag + Ph–Br 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 , 447–471. Eds.; Wiley-VCH: New York, 1998 , pp. 99–166. Eds.; Wiley-VCH: New York, 1998 , pp. 231–269. Cabri, W.; Candiani, I. Acc. Chem. Res. 1995 , 28, 2–7. • Asymmetric: Shibasaki, M.; Boden, C. D. J.; Kojima, A. Tetrahedron 1997 , 53 , 7371–7393. 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 , 2379–2411. X = halide, triflate Mechanism: 2 L; 2 e – Pd(0)L 2 Ph–Pd(II)L 2 –Br oxidative addition syn addition H–Pd(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 , 4133–4135. 2 L; 2 e – Pd(0)L 2 Ph–Pd(II)L 2 –Br oxidative addition syn addition H–Pd(II)L 2 + syn elimination internal rotation reductive elimination Ph–Pd(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 N•HOAc Ozawa, F.; Kubo, A.; Hayashi, T. Chemistry Lett. 1992 , 2177–2180. Andrew Haidle Belestskaya, I. P.; Cheprakov, A. V. Chem. Rev. 2000 , 100 , 3009–3066. • Solid phase: Franzén, R. Can. J. Chem. 2000 , 78 , 957–962. 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 ....
View Full Document

This note was uploaded on 04/07/2008 for the course CHEM 215 taught by Professor Shair during the Fall '07 term at Harvard.

Page1 / 8

The Heck Reaction - R–X CH 3 O 2 C CH 3 O 2 C Pd(II)L 2...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online