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Phosphapalladacycle‐Catalyzed Heck Reactions for Efficient Synthesis of Trisubstituted Olefins: Evidence for Palladium(0) Intermediates
Author(s) -
Beller Matthias,
Riermeier Thomas H.
Publication year - 1998
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/(sici)1099-0682(199801)1998:1<29::aid-ejic29>3.0.co;2-x
Subject(s) - chemistry , catalysis , heck reaction , olefin fiber , yield (engineering) , palladium , base (topology) , aryl , combinatorial chemistry , organic chemistry , medicinal chemistry , mathematical analysis , materials science , alkyl , mathematics , metallurgy
The coupling reaction of 1,1‐disubstituted olefins (α‐methylstyrene, n ‐butyl methacrylate) with various aryl bromides (Heck reaction) has been studied as a new concept to synthesize trisubstituted olefins. Surprisingly, the nature of the base dramatically influences the product distribution. Thus, a systematic investigation on the role of base in Heck reactions of 1,1‐disubstituted olefins was performed. Less coordinating bases like NaOAc, NaOBz or Na 2 CO 3 yield a statistical distribution of regioisomers with the terminal olefin 10 as the major product. However, by using amines like Bu 3 N or diisopropylethylamine (DIPEA) as base internal olefins can be synthesized with high selectivities. With phosphapalladacycle 3 as catalyst precursor, we were able to obtain catalyst turnover numbers up to 1000, while Pd(OAc) 2 /2PPh 3 was one order of magnitude less active. Analysis of the reaction profile by kinetic investigations led to the postulation of a reduction and subsequent oxidative addition of the catalyst precursor 3 to form 12 as catalytically active intermediate.