Catalytic asymmetric 1,6-conjugate addition of in situ generated para-quinone methides with tritylthiol

Abstract

An asymmetric phase-transfer catalyzed 1,6-conjugate addition of in situ generated para-quinone methides with tritylthiol has been developed.

Multicomponent Synthesis of S-Benzyl Dithiocarbamates from para-Quinone Methides and Their Biological Evaluation for the Treatment of Alzheimer’s Disease

“…20 In this context, 1,6-Michael addition reactions with carbon, phosphorus, and nitrogencentered nucleophiles were well-demonstrated in the p-QMs system in the presence of different catalysts and bases. 21 In the case of sulfur nucleophiles, chiral phosphoric acid-catalyzed enantioselective addition of thioacetic acid, 22 chiral phasetransfer catalyst-promoted asymmetric addition of tritylthiol, 23 triflic acid-catalyzed addition of thiols, 24 and sulfuric acidphosphine-promoted regioselective thiolation of p-QMs with sulfinates 25 were reported. However, the 1,6-addition of dithiocarbamic acid to p-QMs is not yet investigated.…”

Enantioconvergent Substitution Reactions of Racemic Electrophiles by Organocatalysis

“…Li and co‐workers reported an enantioselective 1,6‐conjugate addition of tritylthiol 13 to prochiral para ‐quinone methides generated in situ from 4‐hydroxybenzyl p ‐tolyl sulfones 12 using chiral phase‐transfer catalyst ( S )‐ 15 (Scheme 3). [17,18] The reaction that was carried out in the presence of a saturated aqueous solution of Na 2 CO 3 afforded a range of enantioenriched α‐substituted benzyl thioethers 14 in high yields with high enantioselectivities. Racemic α‐substituted sulfones having electron‐deficient aryl groups, such as 4‐CF 3 C 6 H 4 and 2‐CF 3 C 6 H 4 , which are usually difficult to use in acidic conditions, could be successfully employed in this reaction system.…”

Catalytic Access to 4-(sec-Alkyl)Anilines via 1,6-Conjugate Addition of Grignard Reagents to in Situ Generated aza-p-Quinone Methides

“…However, in situ generation of p -QM from the corresponding phenol has also been also reported, in which case enantioselective reactions require substituents at the 2- and 6- positions. 10 …”

“…We started our studies by selecting sulfone 1a as the model substrate to generate the corresponding aza- p -QM precursor (Table ). While the majority of reports makes use of amino alcohols as substrate to generate QM, , we found that in our case these compounds are quite unstable if the N atom is not protected, and therefore not suitable for catalysis.…”