Benzenethiolate Michael addition

Nucleophilic Substitution Reactions. Many of the transformations realized through Michael additions to quinones can also be achieved using nucleophilic substitution chemistry. In some instances die stereoselectivity can be markedly improved in this fashion, e.g., in the reaction of benzenethiol with esters (R = CH3C=0> and ethers (RJ = CH,) of 1,4-naphthoquinones. 2-Bromo-5-acetyloxy-1,4-naphthoquinone, R1 — Hr, yields 75% of 2-thiophenyl-5-acetyloxy-1,4-naphdloquinone. R1 = SCr.Hv 3-Bronio-5-methoxy-l,4-naplitlioquinone, R2 = Br, yields 82% of 3-thiophenyl-5-methoxy-1,4-naphthoquinone R2 = SCr.IIs. 

Although chiral induction has been observed in the Michael addition of various benzenethiols to l,4-systems such as cyclohex-2-en-l-one (15). in the presence of chiral, N-substituted porphyrin bases only the racemic mixture is obtained for pentafluorobenzenethiol (6), albeit in high chemical yield. ... 

Michael addition of benzenethiolate to 4-f-butyl-l-cyanocyclohexene gives only products containing an axial PhS group the same result was obtained from ethyl 4-r-butylcyclohexene-l-carboxylate. In contrast, the addition of diethyl sodiomalonate gave only the equatorial malonate group under thermo-... 

The rate-determining step is assumed to be Michael addition of the benzenethiol moiety to the carbon-carbon double bond of a,/i-unsaturated carbonyl compound. Specific MW effects can be thus expected when considering evolution of the polarity during the reaction progress. The transition state is more polar than the ground... 

Asymmetric Michael addition of benzenethiol to 2-cyclohexenone and maleic acid esters proceeds enantioselectively in their crystalline cyclodextrin complexes. The adducts were obtained in 38 and 30% ee respectively. In both cases, the reaction was carried out in water suspension (Scheme 31). ... 

An example of asymmetric Michael addition carried out in water is the reaction of aromatic thiols with 2-cyclohexanone and maleic acid esters via formation of their crystalline CD complexes [40]. The best chiral inductions (ee ca. 30%, yield 50-93%) were obtained by the combination of the crystalline p-CD complex of benzenethiol with 2-cyclohexenone and octyl maleate, respectively. The opposite combination gives very low ee. 

Kumar A, Salunkhe RV, Rane RA, Dike SY. Novel catalytic enantioselective protonation (proton transfer) in Michael addition of benzenethiol to a-acrylacrylates synthesis of (5)-naproxen and a-arylpropionic acids or esters. J. Chem. Soc. Chem. Commun 1991 485-486. 

In 2011, Vaccaro et al. and Kobayashi et al. independently reported on chiral Sc(OTf)3/bipyridine-catalyzed sulfa-Michael additions to enones 264 in water. High yields and enantioselectivities were obtained for aliphatic thiols and acyclic enones, but the use of benzenethiol or cyclohex-enone failed to deliver optimal selectivity. 

Addition Reactions. The addition of nucleophiles to quinones is often an acid-catalyzed, Michael-type reductive process (7,43,44). The addition of benzenethiol to 1,4-benzoquinone (2) was studied by A. Michael for a better understanding of valence in organic chemistry (45). The presence of the reduced product thiophenyUiydroquinone (52), the cross-oxidation product 2-thiophenyl-1,4-benzoquinone [18232-03-6] (53), and multiple-addition products such as 2,5-(bis(thiophenyl)-l,4-benzoquinone [17058-53-6] (54) and 2,6-bis(thiophenyl)-l,4-benzoquinone [121194-11-4] (55), is typical ofmany such transformations. 

Michael-aldol reaction tandem. Addition of lithium benzenethiolate to conjugated esters in the presence of aldehydes is followed by an aldol reaction in a stereoselective manner. 

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