Catalytic Asymmetric Conjugate Addition of Mercaptans to β‐Substituted‐β‐Trifluoromethyl Oxazolidinone Enoates: Access to Chiral Trifluoromethylated Tertiary Thioethers and Thiols

Abstract

The first asymmetric conjugate addition of mercaptans to b-substituted-b-trifluoromethyl oxazolidinone enoates has been developed. The opposite enantiomers of adducts, containing a trifluoromethylated hetero-quaternary stereogenic centers, could be obtained by utilizing two pseudo-enantiomeric Cinchona alkaloid-derived tertiary amine/squaramides as catalysts. Potassium dihydrogen phosphate was found to accelerate the reaction rate without com-promising the enantioselective excess. A variety of chiral trifluoromethylated tertiary thioethers and thiols were readily prepared with excellent enantioselectivity.

Masked Unsaturated Esters/Amides in Asymmetric Organocatalysis

“…To this aim, β‐trifluoromethyl‐substituted oxazolidinones 1 E were employed in combination with cinchona alkaloid‐derived squaramide IV and potassium dihydrogen phosphate as catalyst and basic additive, respectively. The desired adducts 13 were formed in good to excellent yields and enantioselectivities (Scheme ) 11. By the application of known methanolysis (condition A) or aminolysis (condition B) conditions, these intermediates are easily transformed into simple esters or amides (14,…”

Access to Spirocyclic Benzothiophenones with Multiple Stereocenters via an Organocatalytic Cascade Reaction

“…Over the past decade, several organocatalytic methods have been developed to construct various sulfur-containing heterocycles with a tetrasubstitued chiral carbon . Since the pioneering work by Córdova et al based on the sulfa-Michael addition-initiated construction of tetrahydrothioxanthones, various enantioselective sulfa-Michael additions have been developed using electron-deficient alkenes, such as enones, ,, dienones, acrylates, and unsaturated amides . Other valuable protocols for the synthesis of enantiomerically enriched, sulfur-bearing full-substituted carbon stereocenters include Mannich reactions of thiols into ketimines and electrophilic sulfenylation reactions of α-branched aldehydes, β-keto esters, nitroacetates, oxindols, benzofuran-2­(3 H )-ones, and oxazolones. , An alternative organocatalytic strategy for the preparation of such enantiomerically enriched compounds containing a sulfur-bearing full-substituted stereogenic center is based on the stereoselective formation of C–C or C–N bonds using prochiral sulfur-based substrates, such as α-sulfenylated acrylates and enals, rhodanines, 3-thiooxindoles, and thiazolones. , Yet, only a few reports on organocatalytic reactions on benzo­[ b ]­thiophene derivatives have been published to date .…”

Synthesis of ferrocenyl- and hetaryl-substituted 2,2,2-trifluoroethanols and their conversion into 2,2,2-trifluoroethanethiols using Lawesson’s reagent

“…However, in that case, the reported yield was low (20%). In recent time, widely applied methods comprise Michael additions of 4methoxyphenylmethanethiol onto 4,4,4-trifluorobut-2-enamides followed by debenzylation [8] or thioacetic acid onto 4,4,4-trifluorobut-2-en-1-ones followed by Et 3 N-catalyzed ester cleavage [9]. In a modified procedure, thioacetic acid as the Michael donor can be replaced by H 2 S [10].…”