C. Chatgilialoglu, C. Ferreri / Tetrahedron xxx (2016) 1e6
5
Scheme 12. Proposed mechanistic pathway for the formation of 26.
consecutive radical reactions can be carried out by (Me3Si)3SiH
without the influence of sulfoxide moiety. The reaction with 1,3-
dithiolane derivatives by (Me3Si)3SiH provided some new mecha-
nistic pathways for further investigation.
below. Tetrahydrothiophene-1-oxide 12 afforded the correspond-
ing sulfide 13 in a 25% yield as identified by GC using commercially
available reference. The isolation and identification of compound
10, formed in a 56% yield, is reported below.
4. Experimental section
4.3. Reaction of benzyl-n-butyl sulfide 11 with (Me3Si)3SiH
4.1. Materials and methods
The compound 11 (0.088 g; 0.49 mmol, 0.20 M) was dissolved in
benzene under an inert atmosphere and added with tris(-
trimethylsilyl)silane (2 equiv) and AIBN (0.2 equiv). After 3.5 h, the
TLC and GC monitoring of the reaction showed the consumption of
starting material, therefore the crude mixture was evaporated un-
der vacuum and the residue was flash chromatographed (n-pen-
tane) to afford butylthiotris-trimethylsilylsilane 10 (0.13 g;
Some of the sulfoxides used in this work and sulfides as refer-
ence products are commercially available (2, 12, 13, 15, 16, 17, 18, 19,
20, 21) (SigmaeAldrich, Milan) and were used as received. Pub-
lished synthetic procedures for the benzyl sulfoxide 9 and benzyl n-
butyl sulfide 11 were used.22 2,2-dimethyl-1,3-dithiolane 21, and
the corresponding 1-oxide 25, and 1,1-dioxide 23 were prepared
and identified following published procedures.23 Benzene and
toluene were obtained of HPLC grade (SigmaeAldrich, Milan) and
used as received. Gas chromatography (GC) was carried out to es-
timate the reaction efficiency, using an HP5890 Series II equipment
(Agilent, Milan) using standard references of sulfoxides and sulfides
for calibration, by splitless injection on a 30 mꢃ0.25 mm cross
linked 5% phenylsilicone capillary column (HP5) and hydrogen as
carrier gas at the rate of 2 mL/min with the following oven pro-
gram: 70 ꢂC for 1 min followed by an increase of 15 ꢂC/min up to
280 ꢂC. Calibration procedures were performed by using reference
compounds of all materials, commercially available or isolated and
characterized as herein described. Four different solutions at in-
creasing concentrations were prepared and injected at the same
instrumental conditions, to build-up a calibration curve for the GC
peak area of each compound, and use it as external standard for the
quantitation of the peak areas obtained from each reaction. GC/MS
was carried for the reaction follow-up and product identification
using the above-described equipment and conditions, interfaced
with a mass-selective detector HP5972 (Agilent, Milan). 1H, 13C and
29Si NMR spectra were recorded on a Varian VXR-200 spectrometer
at 200, 50.3 and 39.7 MHz, respectively using CDCl3 or C6D6 as
solvents and solvent residual signals at 7.26 (H)e77.16 (C) ppm and
7.16e128.06 ppm, respectively as reference peaks as well as for 29Si
following reported reference peaks.24 IR spectra were recorded on
a Perkin Elmer Spectrum RX apparatus using CDCl3 solutions.
0.39 mmol; 79% yield) as an oil. 1H NMR (CDCl3)
d 0.20e0.25 (br s,
27 H, CH3), 0.90 (t, 3H, CH3, J¼6.6 Hz), 1.42 (sextet, 2 H, CH2,
J¼6.6 Hz), 1.57 (dt, 2 H, CH2, J¼6.6, 7.1 Hz), 2.52 (t, 2H, CH2,
J¼7.1 Hz); 13C NMR (CDCl3)
d
0.8, 13.6, 22.0, 30.5, 35.3. 29Si NMR
(C6D6)
d
ꢁ56.8 (SieS), ꢁ11.5 (SiMe3) IR (CDCl3) 1246 (SiMe3) cmꢁ1
.
GC/MS m/z: 336 [Mþ], 279 [MꢁC4H9].
4.4. Reduction of aryl sulfoxides
To a magnetically stirred solution of aryl sulfoxide (0.18 M;
50 mg, ca. 2.5 mmol) in toluene (ca. 1.5 mL) kept under inert at-
mosphere, tris(trimethylsilyl)silane (2 equiv) and AIBN (0.2 equiv)
were consecutively added and the reaction mixture was warmed
up at 80 ꢂC. The reaction was monitored by gas chromatography,
after calibration of the equipment using the reference compounds.
The consumption of the starting material was evidenced by GC
together with the formation of the sulfide product, and quantita-
tively evaluated by the calibration curves of commercially available
compounds.
Phenyl methyl sulfoxide 15 gave quantitative yield of its corre-
sponding sulfide 16 using the above described conditions and
4 equiv of the reducing agent. Diaryl sulfoxide 18 and di-p-tolyl
sulfoxide 19 were transformed in 4 h quantitatively in the corre-
sponding sulfides. Di-p-Cl phenyl sulfoxide 20 gave the corre-
sponding sulfide (40% yield), together with the recovery of the
starting material (60% yield).
4.2. Reduction of dialkyl sulfoxides
To a magnetically stirred solution of the dialkyl sulfoxide (0.2 M;
50 mg, 0.25e0.31 mmol) in benzene (1.3e1.5 mL) kept under inert
atmosphere, tris(trimethylsilyl)silane (3 equiv) and AIBN
(0.3 equiv) were consecutively added and the reaction mixture was
heated at 80 ꢂC for 6 h. The reaction was monitored by gas chro-
matography and GC/MS, after calibration of the equipment using
the reference compounds. Flash chromatography of the crude re-
action mixture in the appropriate eluent system was used in order
to separate and identify products.
Di-n-butyl sulfoxide 2 afforded di-n-butyl sulfide in a 41% yield
as determined by GC identification and calibration with commer-
cially available reference. Benzyl-n-butyl sulfoxide 9 afforded the
silyl-sulfide 10 in a 61% yield, as shown in Scheme 5 of the main
text. The isolation and identification of compound 10 is reported
4.5. Reduction of 1,3-dithiolane compounds
4.5.1. Reaction of 1,3-dithiolane 21. The compound 21 (0.2 g;
1.49 mmol, 0.18 M) was stirred in toluene under inert atmosphere
and added with tris(trimethylsilyl)silane (2 equiv) and AIBN
(0.2 equiv). The reaction mixture was left for 1 h at 93 ꢂC, the course
of the reaction being followed by TLC (n-hexane) and GC/MS. The
reaction was evaporated under vacuum, the crude product was
dissolved in n-pentane and flash-chromatographed on silica gel
with n-pentane as the eluent, affording the product, 2-propyl-sul-
fanylethylsulfanyl-tris(trimethylsilyl)silane 22 (0.56 g; 1.46 mmol;
98% yield) as an oil. 1H NMR (CDCl3)
d 0.15e0.25 (s, 27H, CH3), 1.25
(d, 6H, CH3, J¼6.8 Hz), 2.67e2.72 (br m, 4H, CH2), 2.92 (m, 1H,
CHMe2, J¼6.8 Hz); 13C NMR (CDCl3)
d
0.7, 23.5, 30.8, 33.3. 35.2; 29Si