Palladium catalyzed-dehalogenation of aryl chlorides and bromides using phosphite ligands
摘要:
The catalytic system based on Pd-phosphite for the dehalogenation reactions of aryl chlorides and bromides is described. The Pd-phosphite catalyst effectively promoted the dehalogenation of aryl halides to give dehalogenated products in moderate to excellent yields. The aryl chlorides required strong bases such as (NaOBu)-Bu-t for this transformation, whereas the aryl bromides were dehalogenated in the presence of weak bases such as Cs2CO3. This catalytic system exhibited tolerance to functional groups such as methoxy, amine, hydroxyl, ether, amide, benzyl and ketone groups. It also demonstrated chemoselectivity in that bromochlorobenzene was converted only to chlorobenzene. (C) 2008 Elsevier B. V. All rights reserved.
A class of pyrazole derivatives is described for use in treating p38 kinase medicated disorders. Compounds of particular interest are defined by Formula IA
wherein R
1
, R
2
, R
3
and R
4
are as described in the specification.