High Performance of a Palladium Phosphinooxazoline Catalyst in the Asymmetric Arylation of Cyclic N‐Sulfonyl Ketimines

Abstract

A cationic palladium complex with a chiral phosphine-oxazoline ligand (iPr-phox) showed high catalytic activity and enantioselectivity in the asymmetric addition of arylboronic acids to six-membered cyclic N-sulfonyl ketimines to give high yields of the corresponding chiral cyclic sulfamidates with 96-99.9% ee. The products have tetrasubstituted stereogenic centers with an amino group and a triaryl or alkyldiaryl group as substituents.

Pd‐Catalyzed Asymmetric Addition of Arylboronic Acids to Pyrazolinone Ketimines

“…Exchanging Pd(TFA) 2 for Pd(OAc) 2 and PdCl 2 led to the low level of asymmetric induction (entries 12–13). Other types of ligands widely used in asymmetric addition of arylboronic acids to ketimines such as In‐Pyrox ( L 5 ) , [18] t ‐Bu‐Nicox ( L 6 ), [19] i ‐Prox ( L 7 ) [20] and Phosphine‐imine ( L 8 ) [21] were also tested, and all of them did not show any improvement on the rection yields and enantioselectivities by using DCE as the reaction media (entries 14–17). The results were still unsatisfactory even when the reactions were conducted under previously reported reaction conditions (entries 19–20) [18,19] …”

Palladium‐Catalyzed Asymmetric Arylation of Trifluoromethylated/Perfluoroalkylated 2‐Quinazolinones with High Enantioselectivity

“…Complementary to enzymatic approaches by transamination of ketones, asymmetric addition of arylboron reagents to aldimines and ketimines catalyzed by chiral rhodium and palladium complexes has emerged as of one of the most efficient methods . Compared with aldimines, ketimines are more challenging substrates because they are much less reactive due to the presence of the substituent on the azomethine carbon . Recently, cyclic ketimines have become favorable substrates in asymmetric arylation reactions; the enantioselectivity of these reactions is generally higher due to the suppression of syn‐anti isomerization of the carbon–nitrogen double bond in cyclic ketimine structures.…”

“…The results are summarized in Table . A cationic palladium complex coordinated with chiral phosphine‐oxazoline ligand ( S )‐ i Pr‐phox, which has been reported as an effective catalyst for the asymmetric arylation of sulfonyl imines, was found to also be effective in this study. The reaction of 1 a with 2 equiv of phenylboronic acid ( 3 a ) in the presence of 5 mol % of a cationic palladium catalyst generated in situ from PdCl 2 [( S )‐ i Pr‐phox] (5 mol %) and AgBF 4 (15 mol %) in 1,2‐dichloroethane at 65–70 °C for 12 h gave 97 % yield of the phenylation product 4 a .…”

Enantioselective synthesis of gem-diarylalkanes by transition metal-catalyzed asymmetric arylations (TMCAAr)

“…Pd-catalyzed enantioselective additions of arylboronic acids to cyclic N -sulfonyl ketimines were disclosed by Zhang 41 a and Lu/Hayashi 42 using chiral pyridine-oxazoline ( L32 ) and phosphine-oxazoline ( L31 ) ligands, respectively ( Scheme 22 ). Analogously, the enantioselective 1,2-addition of arylboronic acids to 3-ketimino oxindoles, by the Zhang group, 41 b was catalysed by a Pd( ii )/ L33 complex and enables the synthesis of enantioenriched 3-amino-3-aryl-2-oxindoles with high ee.…”