No abstract

The use of 5,5-(dimethyl)-i-Pr-PHOX as a practical equivalent of t-Bu-PHOX in asymmetric catalysis is reported. This new member of the phosphinooxazoline (PHOX) ligand family behaves similarly in terms of stereoinduction to t-Bu-PHOX with the key advantage of being readily accessible as both enantiomers starting from either (S)- or (R)-valine.

The enantioselective Pd-catalyzed allylation reaction of fluorinated allyl enol carbonates is presented; a key feature of this transformation is the important effect of the ligand-to-palladium ratio on the enantioselectivity of the alpha-fluoroketones, since using a ligand excess (L/Pd ratio = 1.25 : 1) led to moderate results (30-76% ee), while using a L/Pd ratio <1 : 1.67 (to as low as 1 : 4) allowed the desired products to be obtained with high enantiopurity (up to 94% ee).

The design, synthesis, and applications of potential substitutes of t-Bu-PHOX in asymmetric catalysis is reported. The design relies on the incorporation of geminal substituents at C5 in combination with a substituent at C4 other than t-butyl (i-Pr, i-Bu, or s-Bu). Most of these new members of the PHOX ligand family behave similarly in terms of stereoinduction to t-Bu-PHOX in three palladium-catalyzed asymmetric transformations. Electronically modified ligands were also prepared and used to improve the enantioselectivity in the Pd-catalyzed allylation reaction of fluorinated allyl enol carbonates.

Enantioselective syntheses O 0031Enantioselective Pd-Catalyzed Allylation Reaction of Fluorinated Silyl Enol Ethers. -The reaction is examined in a range of five-, six-, and seven-membered ketones. In all cases good to excellent yields and excellent enantioselectivities are obtained. -(BELANGER, E.; CANTIN, K.; MESSE, O.; TREMBLAY, M.; PAQUIN*, J.-F.; J. Am. Chem. Soc. 129 (2007) 5, 1034-1035; Dep. Chim., Univ. Laval, Laval, Que. G1K 7P4, Can.; Eng.) -Bartels 24-030