ISSN:
1434-1948
Keywords:
Catalysis
;
Palladium
;
C-C coupling
;
Metallacycles
;
Trisubstituted olefins
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
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 Na2CO3 yield a statistical distribution of regioisomers with the terminal olefin 10 as the major product. However, by using amines like Bu3N 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)2/2PPh3 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.
Type of Medium:
Electronic Resource
Permalink
