The Stille Reaction

The Stille Reaction - catalyst RX Pd(II) BrSnBu 3 PhSnBu 3...

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Unformatted text preview: catalyst RX Pd(II) BrSnBu 3 PhSnBu 3 PhSnBu 3 Bu 3 SnBr MX RI Pd(II)L 2 X H Pd(PPh 3 ) 4 Pd(OAc) 2 Pd R L I L O Pd L L I R Chem 215 Myers Reviews: Farina, V.; Krishnamurthy, V.; Scott, W. J. Org. React. 1998 , 50 , 1652. Stille, J. K. Angew. Chem., Int. Ed. Engl. 1986 , 25 , 508524. Mitchell, T. N. In Metal-catalyzed Cross-coupling Reactions , Diederich, F., and Stang, P. J., Eds.; Generalized Cross-Coupling: R'M R and R' are sp 2 hybridized Wiley-VCH: New York, 1998 , pp. 167202. RR' X = I, OSO 2 CF 3 , Br, Cl M = Sn, B, Zr, Zn catalyst = Pd (sometimes Ni) Mechanism: Pd(0)L n p-TolBr oxidative addition reductive elimination transmetalation p- TolPd(II)L m Br p- TolPd(II)L m Ph p-TolPh Farina, V.; Krishnamurthy, V.; Scott, W. J. The Stille Reaction ; John Wiley & Sons: New York, 1998 . A specific example: Transmetalation is proposed to be the rate determining step with most substrates. -hydride elimination can be a serious side reaction within alkyl palladium intermediates. Oxidative addition and reductive elimination steps occur with retention of configuration for sp 2-hybridized substrates. Many functional groups are tolerated (e.g., CO 2 R, CN, OH, CHO). Relative order of ligand transfer from Sn: alkynyl > alkenyl > aryl > allyl = benzyl > -alkoxyalkyl > alkyl The details of the mechanism are still being elucidated, and the mechanism may change with Casado, A. L.; Espinet, P. J. Am. Chem. Soc. 1998 , 120 , 89788985. Stille Reaction conditions: Catalyst: Commercially available Pd(II) or Pd(0) sources. Examples: Pd 2 (dba) 3 Typically: p-TolBr + Pd catalyst p-TolPh + Oxidative addition initally gives a cis complex that rapidly isomerizes to its trans isomer: PdL 2 cis trans fast HPd(II)L 2 X + different reaction conditions: dba = Casado, A. L.; Espinet, P. Organometallics 1998 , 17 , 954959. Andrew Haidle Intramolecular: Duncton, M. A. J.; Pattenden, G. J. Chem. Soc., Perkin Trans. 1 1999 , 12351246. Solid phase: Franzn, R. Can. J. Chem. 2000 , 78 , 957962. The Stille Reaction I S n B u 3 F a r i n a , V . ; K a p a d i a , S . ; K r i s h n a n , B . ; W a n g , C . ; L i e b e s k i n d , L . S . J . O r g . C h e m . 1 9 9 4 , 5 9 , 5 9 5 5 9 1 1 . A d d i t i v e s : C u I c a n i n c r e a s e t h e r e a c t i o n r a t e b y > 1 2 . r e l a t i v e r a t e 1 1 1 1 4 P d 2 ( d b a ) 3 ( 5 m o l % ) P P h 3 ( 2 m o l % ) d i o x a n e , 5 C m o l % C u I T h e r a t e i n c r e a s e i s a t t r i b u t e d t o t h e f r e e l i g a n d s c a v e n g i n g a b i l i t y o f C u I ; s t r o n g l i g a n d s i n s o l u t i o n a r e k n o w n t o i n h i b i t t h e r a t e- l i m i t i n g t r a n s m e t a l a t i o n s t e p ....
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The Stille Reaction - catalyst RX Pd(II) BrSnBu 3 PhSnBu 3...

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