Hetero-Michael addition of benzenethiol to cycloalkenones using cation-exchanged faujasites: Simultaneous acid–base bifunctional catalysis

Zeolites as Catalysts for the Synthesis of Fine Chemicals

“…Thia-Michael additions of benzenethiol to cyclic alkenones have been recently performed using cation-exchanged faujasites with different Si/Al ratios (Scheme 25.45). Reactions were performed in hexane solution at 0 • C, and the results showed that NaY and KY zeolites were the best catalysts in terms of activity and selectivity to the Michael adduct (90-93% conversion, 100% selectivity) [243]. However, as with most basic X zeolites, although they also exhibit very good activity for the Michael addition, significant side reactions take place in which tiols are oxidized to disulfide.…”

Sequential Ytterbium(III) Triflate Catalyzed One‐Pot Three‐Component Thia‐Michael Addition

“…Conventional methods for thia‐Michael reactions involve the addition of a free thiol to a Michael acceptor in the presence of a strong base as the catalyst . More recently, numerous reagents and catalysts, including Brønsted acids [e.g., NH 4 Cl, B(OH) 3 , and Tf 2 NH (Tf=trifluoromethanesulfonyl)], Lewis acids [e.g., BF 3 ⋅ OEt 2 , ZrCl 4 , Hf(OTf) 4 , Cu(BF 4 ) 2 ⋅ x H 2 O, Zn(ClO 4 ) 2 ⋅ 6H 2 O, InBr 3 , Bi(NO 3 ) 3 , FeCl 3 , VO(OTf) 2 , and Ln(OTf) 3 (Ln=lanthanide)], heterogeneous catalysts [e.g., HBF 4 ‐SiO 2 , HClO 4 ‐SiO 2 , silica nanoparticles, and zeolite], ionic liquids, and other reagents [e.g., I 2 , H 2 O, N‐heterocyclic carbenes, ceric ammonium nitrate (CAN), and tetrabutylammonium hydroxide (TBA‐OH)], have been developed for carbon‐sulfur bond formation reactions (Scheme a). Although numerous methods exist to efficiently perform thia‐Michael additions, one disadvantage is that the thiol group has a propensity toward slow oxidation towards disulfide formation under ambient conditions.…”

Preparation of 2-heteroatom substituted 4-oxo-4-arylbutanoates via thio- and aza-Michael addition

“…7,8 Indoles underwent conjugate addition to 4-aryl-4-oxobut-2-enoates, forming a C-C bond, catalyzed by a Lewis acid. Although thio-Michael addition has been intensively studied, [11][12][13][14][15][16][17][18][19] only a few unusual approaches to certain specific 2-arylthio-4-oxo--4-arylbutanoates have been reported. 10 In our recent program focused on the selective reduction of 2-heteroatomsubstituted carbonyl compounds, some 2-heteroatom-substituted 4-oxo-4-arylbutanoates were required.…”