Lewis acid-promoted oxidative addition of thioimidates to Pd0.
The isomeric S-methyldihydropyrrins 9-Z and 9-E exhibit markedly different behavior in Pd(0)-catalyzed cross-coupling reactions. Thioimidates 9-Z are readily converted to imines 10-Z employing Pd(0)/AlkZnI. Under identical conditions 9-E are inert. Oxidative addition to Pd(0) requires activation by Zn or other Lewis acids, which is sterically unfavorable with 9-E. Analogous results were obtained with the related thioimidates 11-E,Z as well as with methylthiopyridines 19alpha-gamma. In the case of both 11 and 19 oxidative addition to Pd(0) was greatly facilitated in the presence of BF(3) x Et(2)O. The importance of Lewis acid activation to Pd(0) oxidative addition in such substrates appears to be a general phenomenon not previously recognized.
Ghosh
Indranath
I
Burke Chemical Laboratory, Dartmouth College, Hanover, New Hampshire 03755, USA.
Jacobi
Peter A
PA
D002384:Catalysis; D002625:Chemistry, Organic / Q000379:methods; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010165:Palladium / Q000737:chemistry*; D013237:Stereoisomerism; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry
D007202:Indicators and Reagents; D009942:Organometallic Compounds; D013438:Sulfhydryl Compounds; D010165:Palladium; D015032:Zinc