Phenylthio- Ketones

Acyl anions require special chemistry because they have umpolung of reactivity specific enols have normal reactivity but the problem of regioselectivity must be solved. The carbonyl compound must enolise under the reaction conditions only on the required side and, as carbonyl compounds are also electrophilic, it must not condense with itself under these conditions. 

Unfortunately, the usual routes to a-PhS ketones 94, from the parent ketone33 6i, 62) by sulphenylation or halogenation, themselves require a solution of the specific enol problem This can be found if silyl enol ethers are combined with PhSCl63). 

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The reaction of crotonaldehyde and methyl vinyl ketone with thiophenol in the presence of anhydrous hydrogen chloride effects conjugate addition of thiophenol as well as acetal formation. The resulting j3-phenylthio thioacetals are converted to 1-phenylthio-and 2-phenylthio-1,3-butadiene, respectively, upon reaction with 2 equivalents of copper(I) trifluoromethanesulfonate (Table I). The copper(I)-induced heterolysis of carbon-sulfur bonds has also been used to effect pinacol-type rearrangements of bis(phenyl-thio)methyl carbinols. Thus the addition of bis(phenyl-thio)methyllithium to ketones and aldehydes followed by copper(I)-induced rearrangement results in a one-carbon ring expansion or chain-insertion transformation which gives a-phenylthio ketones. Monothioketals of 1,4-diketones are cyclized to 2,5-disubstituted furans by the action of copper(I) trifluoromethanesulfonate. ... 

Ring expansion.1 The adducts (2) of cycloalkanones with 1 on reaction with methyllithium or wc-butyllithium at 0° rearrange to ring-expanded a-phenylthio ketones. 

Studies on sulfur-substituted 2-pyridones have shown (99M545) that unsaturated phenylthio ketones 90 can yield aminopyrans 91 with MN 27a, while enaminone (X = NMe2) gives 2-pyridones 92 (Scheme 26). 

I.4.I.2. Amino, Hydroxy, and Phenylthio Ketones Asymmetric hydrogenation of amino ketones, in either a neutral or hydrochloride form, has extensively been studied. Both Rh(I) and Ru(II) complexes with an appropriate chiral diphosphine give a high enantioselectivity. As described in Scheme 1.42, a-aminoacetophenone hydrochloride is hydrogenated using a cationic Rh complex with (R)-MOC-BIMOP, an unsymmetricaJ biaryl diphosphine, to give the... 

Reaction with various electrophilesThe anion (2, n-BuLi) of 1 in the presence of TMEDA forms adducts with esters, which on chromatography produce tx-phenylthio ketones (equation I). Other useful reactions are formulated in equations (II) and (III). 

Intermediate 3 can either be isolated or used in situ for further elaboration. Fluoride-5 and Lewis-acid catalyzed aldol reactions cleanly give aldol adducts,5 and the reaction with phenylsulfenyl chloride gives a-phenylthio ketones in high yield.5... 

Phenylthio ketones, asymmetric hydrogenation, 10, 47 Phenylthiourea, with trinuclear Os clusters, 6, 747 Phenyltris(A r/-butylthio)methylborato ligands, in cobalt(II) complexes, 7, 18... 

Silveira, C. C. Bemardi, C. R. Braga, A. L. Kaufman, T. S. Elaboration of 1-benzoyltetra-hydroisoquinoline derivatives employing a Pictet-Spengler cyclization with a-chloro a-phenylthio ketones. Synthesis of O-methyl-velucryptine. Tetrahedron Lett. 2001, 42, 8947-8950. 

Reduction of a-methylthio ketones, a-Methylthio and a-phenylthio ketones (1) are reduced with high selectivity to sy/i-alcohols (2) by this complex hydride, except when... 

A similar reaction with sodium benzenethiolate results in a-phenylthio ketones. Example ... 

The oxidation of sulfides to sulfoxides is a facile transformation for which many reagents have been employed in the literature. These include hydrogen peroxide, ozone, nitric acid, chromic acid or tert-butylhypochlorite. Here, meto-chloroperbenzoic acid is used to oxidize a-phenylthio ketone 14, and successive elimination of the resulting a-phenylsulfinyl ketone 15 by heating at reflux in benzene provides the or,ji3-unsaturated ketone 16. Because of their thermal instability sulfoxides easily undergo elimination. The mechanism is explained by Cram as stereospecific cw-elimination. ... 

Phenylthio ketones are also enantioselectively hydrogenated with a BINAP-, MeO-BIPHEP (3)-, or BDPP (8)-Ru complex without any deactivation of catalyst to give the chiral thio alcohols in up to 98% e.e. [173]. The reactivity and selectivity are somewhat decreased when a y-phenylthio analogue is used as substrate, however. 

The reactions with esters of stabilized anions (32) and (38) give a-phenylthio ketones in yields of 75-82% (equation 37).2 Acylations with succinic anhydride and butyrolactone to give y-keto acids and y-hydiDxy ketones respectively, also proceed in good yields. ... 

Methoxy-a-(phenylthio) ketones, e.g., 3-methoxy-l-phenyl-2-phenylthiopropanone and 5-methoxy-l-phenyl-4-phenylthio-l-penten-3-onc (Table 6), can also be reduced with syn selectivity by zinc borohydride. calcium borohydride and lithium triethylborohydride82. For zinc and calcium borohydride, at least, it is reasonable to suppose that the transition state 4 (where R3 = MOM) is reinforced by /1-chclation. These reagents are actually more successful than L-Selectride in the reduction of 3-methoxy-1-phenyl-2-phenylthiopropanone, where the L-Se-lectridc result is anomalously poor. A /5-hydroxy substrate, 3-hydroxy-2-mcthylthio-l-phenyI-propanone, could be reduced to 2-methylthio-l-phenyl-l,2-propanediol with good syn selectivity using zinc borohydride (yield 65% d.r. 93 7)81. 

Chiral a-phenylthio ketones may be prepared in good yields and high by the reaction of tin (II) enolates with thiosulphonates in the presence of chiral diamines (Scheme 32). 

Desulfurization. Japanese chemists have found that a-phenylthio ketones are desulfurized by zinc and chlorotrimethylsilane in ether as shown in equation (I). 

Phenylthio-2-cyclopentenone, 33 a-Phenylthio ketones, 532-533 l-Phenylthio-2-methoxy-1,3-butadiene,... 

Several reports are concerned with the preparation of benzo[6]thiophenes by acid-catalyzed cyclization of 2-(phenylthio)ketones including the improved synthesis of (221) and (223) from (220) and (222), respectively <88JHC1271> see also <92BRP2253847,93EUP556680>. 

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