Polystyrene-Supported Phosphine-Catalyzed aza-Baylis-Hillman Reactions and the Relationship between Resin Loading Level and Catalyst Efficiency

摘要

The Baylis-Hillman reaction has become an important tool in organic synthesis,since it allows for the formation of carbon-carbon bonds under mild reaction conditions.While early versions of this reaction were marked by some irreproducible results and long reaction times,recent years have seen much advancement in the understanding of its mechanism and improvements in its efficiency and reliability.Aggarwal and co-workers have been among the many researchers at the forefront of elucidating the mechanistic nuances of this reaction and have recently reported a definitive study describing the relationship between the pK_a of an amine and its effectiveness as a catalyst in Baylis-Hillman reactions.In their work,it was found that quinuclidine,with its relatively high pK_a,is a much better catalyst than the more commonly used l,4-diazabicyclo[2.2.2]octane,with its relatively low pK_a.In fact,it is reported that quinuclidine is the most effective amine catalyst yet examined for Baylis- Hillman reactions and that it allows for previously unreactive substrates to participate in such reactions.