No abstract

The preparation of various potassium organotrifluoroborates bearing either aryl, alkenyl, or alkynyl substituents is described. These stable salts are shown to be very efficient partners in palladium‐catalysed cross‐coupling reactions with arenediazonium salts, affording biaryl and styrene derivatives in high yields.

Potassium trifluoro(organo)borates, highly stable organoboron derivatives, have recently emerged as promising alternatives to other organoboron reagents. These salts have shown interesting reactivity, not only through the intermediate formation of difluoroboranes, but also in transmetallation reactions with transition metals. In numerous re-

Conjugate addition of potassium trifluoro(organo)borates 2 to dehydroalanine derivatives 1, mediated by a chiral rhodium catalyst and in situ enantioselective protonation, afforded straightforward access to a variety of protected alpha-amino esters 3 with high yields and enantiomeric excesses up to 95%. Among the tested chiral ligands and proton sources, Binap, in combination with guaiacol (2-methoxyphenol), an inexpensive and nontoxic phenol, afforded the highest asymmetric inductions. Organostannanes have also shown to participate in this reaction. By a fine-tuning of the ester moiety, and using Difluorophos as chiral ligand, increased levels of enantioselectivity, generally close to 95%, were achieved. Deuterium labeling experiments revealed, and DFT calculation supported, an unusual mechanism involving a hydride transfer from the amido substituent to the alpha carbon explaining the high levels of enantioselectivity attained in controlling this alpha chiral center.

No abstract

No abstract

No abstract

Keywords: Borates / Asymmetric catalysis / Michael addition / Rhodium / Catalysis / EnonesPotassium organotrifluoroborates, highly stable organoboron derivatives, participate in asymmetric 1,4-additions to enones. This reaction, catalyzed by cationic rhodium(I) complexes chelated with binap, MeO-biphep or josiphos ligand, affords 1,4-adducts with high yields and enantioselectivities