Enantioselective CC Bond Formation to Sulfonylimines through Use of the 2‐Pyridinesulfonyl Group as a Novel Stereocontroller

Abstract

Enantioselective CC bond formation to 2‐pyridinesulfonylimines afforded products with good enantioselectivity. Dynamic induction of chirality on the sulfur by coordination of a chiral Lewis acid to the pyridine nitrogen and one of the prochiral sulfonyl oxygens induces enantioselectivity. Since the 2‐pyridinesulfonyl group can easily be removed after the reaction, it acts not only as an activating group but also as an efficient stereocontroller.

Stable synthetic equivalents of N-unsubstituted imines: Part 1. Synthesis

“…The latter reagent is also used for removal of the trifluoromethanesulfonyl protective group. The deprotection of the 2 pyridinesulfonyl protective group is usually achieved in yields higher than 90% using Mg in acetic acid [35] or methanol [36] at 0°C. The mesyl protective group is also removed under reducing conditions by treatment with LiAlH 4 or Na/ t BuOH, HMPA/NH 3 [3], while the PhSH/K 2 CO 3 system in DMF shows good results for the deprotection of the p nitrobenzenesulfonyl group [37].…”

A Cationic High‐Valent Cp*CoIII Complex for the Catalytic Generation of Nucleophilic Organometallic Species: Directed CH Bond Activation

“…We selected cobalt, [10] which is homologous with rhodium but a more abundant first-row transition metal, [11] and investigated the ability of high-valent cobalt catalysts to promote CÀH bond functionalization. Optimization studies with 2-phenylpyridine (2 a) and the sulfonyl imine 3 a [12][13][14] as model substrates are summarized in Table 1. Several commercially available Co II and Co III salts showed no catalytic activity at 100 8C in 1,2-dichloroethane ( Table 1, entries 1 and 3-5).…”

Lewis Base Assisted Brønsted Base Catalysis: Bidentate Phosphine Oxides as Activators and Modulators of Brønsted Basic Lanthanum–Aryloxides

“…A catalytic amount of Lewis basic bidentate phosphine oxide 1 effectively activated and modified the properties of Brønsted basic rare-earth metal aryloxide catalysts, switching the diastereoselectivity from syn to anti in the lanthanum-catalyzed direct Mannich-type reaction. The mechanistic studies, a preliminary trial in a catalytic asymmetric reaction, and the extension of the Lewis base/Brønsted base catalysis to Michael and nitroaldol reactions are also described.We recently reported an iPr-pybox/La(OAr 1 ) 3 (Ar 1 = 4-MeO-C 6 H 4 ) complex which catalyzed the syn-selective direct asymmetric Mannich-type reactions [7] of imines 2 [8] with trichloromethyl ketone 3 a, an ester donor equivalent (Table 1, entry 1). [9,10] During the mechanistic studies of the reaction, we found that the reaction did not proceed with either La(OAr 1 ) 3 alone (Table 1, entry 2,) or iPr-pybox alone (Table 1, entry 3).…”

“…We recently reported an iPr-pybox/La(OAr 1 ) 3 (Ar 1 = 4-MeO-C 6 H 4 ) complex which catalyzed the syn-selective direct asymmetric Mannich-type reactions [7] of imines 2 [8] with trichloromethyl ketone 3 a, an ester donor equivalent (Table 1, entry 1). [9,10] During the mechanistic studies of the reaction, we found that the reaction did not proceed with either La(OAr 1 ) 3 alone (Table 1, entry 2,) or iPr-pybox alone (Table 1, entry 3).…”

“…b-Amino ester 5 ba was obtained in greater than 99 % yield from 4 ba by treatment with NaOMe in MeOH at 0 8C for 10 minutes. Removal of the 2-pyridinesulfonyl group proceeded smoothly with Mg 0 in MeOH at room temperature, [8] to give 6 ba in good yield. Stereoselective reduction of 4 with LiAlH 4 , and subsequent dichlorooxirane formation and stereoselective intramolecular cyclization using NaOH in DME at room temperature gave azetidine carboxylic acids.…”