[17873-08-4] · C10H16SSi · (Phenylthiomethyl)trimethylsilane · (MW 196.42)
Physical Data: bp 158-159 °C/52 mmHg; d20 0.967 g cm-3; n
Solubility: sol most common organic solvents.
Form Supplied in: oil; commercially available.
Analysis of Reagent Purity: by GC or 1H NMR analysis.
Preparative Methods: by reaction of Phenylthiomethyllithium with Chlorotrimethylsilane.4
Purification: by distillation under reduced pressure.
Handling, Storage, and Precautions: irritant; foul smelling; use in a fume hood.
Metalation of the title reagent (1) with n-Butyllithium gives the fairly stable anion phenylthio(trimethylsilyl)methyllithium (2), which is a formyl anion equivalent as illustrated by the sequence in eq 1.1 Anion (2) reacts with primary alkyl bromides and iodides to yield 1-phenylthio-1-trimethylsilylalkanes (3) in high yields. These intermediates are easily oxidized by m-Chloroperbenzoic Acid to the corresponding sulfoxides. Subsequent heating promotes a sila-Pummerer rearrangement5 to produce aldehydes after hydrolysis.1 Reagent (1) is superior to 1,3-Dithiane for the synthesis of aldehydes from alkyl halides, in view of the greater ease of hydrolysis of (3). Application of this procedure to the synthesis of unsymmetrical ketones has also been reported.6
The Zinc Bromide catalyzed alkylation of enol silanes by a-halo-a-(phenylthio)methyltrimethylsilanes (eq 2) provides an efficient method for electrophilic formylation (i.e. an umpolung of the transformation in eq 1) which is useful for the synthesis of b-ketoaldehydes.7 The sequence can also be diverted for the synthesis of b-trimethylsilylenones (eq 2).8
Phenylthiobis(trimethylsilyl)methane (4), prepared by the reaction of (2) with Me3SiCl, serves as a synthetic equivalent of LiCO2Me.9 Metalation of (4) with BuLi in the presence of N,N,N´,N´-Tetramethylethylenediamine gives phenylthiobis(trimethylsilyl)methyllithium (5); subsequent alkylation and electrochemical oxidation achieves chain homologation to form an ester (eq 3). Alternatively, alkylation of (5) with a terminal oxirane followed by cycloelimination in situ generates 1-phenylthio-1-trimethylsilylcyclopropanes.10 Anion (2) itself reacts with oxiranes to give adducts which can also be converted to 1-phenylthio-1-trimethylsilylcyclopropanes, but two intermediary steps are required to accomplish cycloelimination (eq 4).11
Anion (2) adds to aldehydes, ketones, and enones, in the last-named case in either 1,2- or 1,4-manner depending on the reaction conditions.12 In the case of 1,2-addition the b-hydroxysilane adduct usually cannot be isolated owing to rapid elimination (Peterson alkenation) to vinyl sulfides (eq 5), which can be hydrolyzed to the corresponding aldehydes.2 The vinyl sulfides are not formed stereoselectively unless there are proximate bulky substituents.13 Peterson alkenation products have also been observed in the reaction of (2) with amides, ureas, and carbonates.14
The reaction of (2) with esters provides a-phenylthio-a-trimethylsilyl ketones, which can be easily converted to a-phenylthio ketones (eq 6).15 b-Hydroxy sulfides are obtained from the reaction of (1) with carbonyl compounds in the presence of a catalytic amount of fluoride ion (eq 7).16
Lithiated reagent (2) reacts with a-trimethylsilyloxiranes to yield vinylsilanes (eq 8). The reaction involves nucleophilic opening of the oxirane ring by (2), followed by 1,2-elimination of a silyl and a phenylthio group.3
Vinylsilanes are also prepared from (2) as illustrated in eq 9.17 Treatment of (2) with Bis(trimethylsilyl) Peroxide provides (6) which reacts with phosphonium ylides in the presence of Tetra-n-butylammonium Fluoride to give mixtures of vinylsilanes favoring the (Z)-isomer.
In addition to haloalkanes, carbonyl derivatives, and oxiranes, anion (2) reacts with a wide range of other electrophiles including N-Chlorosuccinimide,18 Chlorotrimethylsilane,8 Bu3SnCl,15 Diphenyl Disulfide, and Benzenesulfenyl Chloride,15 and trialkylboranes.19
Methoxy(phenylthio)(trimethylsilyl)methane (7) is prepared by metalation-silylation of phenylthiomethyl methyl ether.20 [Methoxy(phenylthio)(trimethylsilyl)methyl]lithium (8), prepared from (7) by metalation with s-Butyllithium in the presence of TMEDA, undergoes clean and efficient Peterson alkenation with aldehydes to give (E)-ketene-O,S-acetals stereoselectively, which can then be hydrolyzed to thioesters (eq 10).21
The selenium analog of (2) is prepared by deprotonation of (phenylselenomethyl)trimethylsilane with Lithium Diisopropylamide or Lithium 2,2,6,6-Tetramethylpiperidide (eq 11). The anion (9) thus formed can be alkylated in good yields, and the alkylated product can be oxidized to the corresponding selenoxide at low temperature, but selenoxide elimination leading to a vinylsilane competes with the sila-Pummerer rearrangement.22,23
See also 2-Lithio-1,3-dithiane, Phenylthiomethyllithium, and Bis(phenylthio)methane.
Akira Hosomi & Makoto Hojo
University of Tsukuba, Japan
Georges Hareau & Philip Kocienski
Southampton University, UK