Synthesis, metallation and nucleophilic reactivity of 2,6- bis(trialkylsilyl)- 4H -thiopyrans

Article abstract of DOI:10.1080/17415993.2013.789517

We report herein (i) the synthesis of 2,6-bis(trialkylsilyl)-4H-thiopyrans by thionation-cylisation of 1,5-bis(acylsilanes) and (ii) the lithiation of these thiopyrans and reaction of their lithium salt with various electrophiles. Most reaction led to alkylation at carbons in position 4 and 2, the former being generally more regioselective. Partial reaction at sulfur atom occurred in case of n-hexyl bromide. An effective and totally regioselective trimethylsilylation led to a 2,4,6-tris(trialkylsilyl)-4H-thiopyran. Its lithium salt exhibited also interesting properties: Peterson olefination products were formed under reaction with aldehyde, and a stable thiabenzene was effectively obtained with n-hexylbromide. The role of the silyl substituents was decisive to explain the particular aspects of the reactivity of these silyl substituted thiopyrans.

Full text of DOI:10.1080/17415993.2013.789517

Journal of Sulfur Chemistry, 2013
Vol. 34, No. 6, 692–704, http://dx.doi.org/10.1080/17415993.2013.789517
Synthesis, metallation and nucleophilic reactivity of
2,6-bis(trialkylsilyl)-4H-thiopyrans†
Tiziano Nocentini,a,b Jean-Philippe Bouillon,a*,‡ Antonella Capperuccib and Charles Portellaa∗
aInstitut de Chimie Moléculaire de Reims, Université de Reims Champagne-Ardenne, UMR CNRS 7312,
UFR Sciences Exactes et Naturelles, BP 1039, F-51687 Reims Cedex 2, France; bDipartimento di Chimica
“Ugo Schiff”, via della Lastruccia 3-13, I-50019 Sesto Fiorentino (Firenze), Italy
(Received 14 February 2013; final version received 21 March 2013)
We report herein (i) the synthesis of 2,6-bis(trialkylsilyl)-4H-thiopyrans by thionation-cylisation of 1,5-
bis(acylsilanes) and (ii) the lithiation of these thiopyrans and reaction of their lithium salt with various
electrophiles. Most reaction led to alkylation at carbons in position 4 and 2, the former being generally more
regioselective. Partial reaction at sulfur atom occurred in case of n-hexyl bromide. An effective and totally
regioselective trimethylsilylation led to a 2,4,6-tris(trialkylsilyl)-4H-thiopyran. Its lithium salt exhibited
also interesting properties: Peterson olefination products were formed under reaction with aldehyde, and
a stable thiabenzene was effectively obtained with n-hexylbromide. The role of the silyl substituents was
decisive to explain the particular aspects of the reactivity of these silyl substituted thiopyrans.
E
1. n-BuLi
TBS
S
E
TBS
2. "E+"
TBS
S
TBS
TBS
S
TBS
E
TBS
S
TBS
“E+” = RX, TMSCl, RCHO
RX = n-HexBr
Keywords: 4H-thiopyran; thiabenzene; organosilicon; organosulfur; sulfur heterocycles
1. Introduction
Since the first report on the synthesis of 4H-thiopyran in 1962 (1), several papers described the
synthesis and the chemistry of analogues variously substituted, generally on positions 2,6 and/or
4. 4H-Thiopyrans may be considered as both hydride donors and proton donors. Thiopyrilium salts
are produced under oxidative conditions (Cl2, I2, PCl5, Ph3C+ClO4−) (2). Metallation of thiopyrans
gives a conjugated nucleophilic intermediate which can be alkylated, acylated or silylated more or
less regioselectively (3–5). Thiopyrilium salts are themselves good precursors for the preparation
of further substituted derivatives by electrophilic addition (6).
*Corresponding authors. E-mail: charles.portella@wanadoo.fr and jean-philippe.bouillon@univ-rouen.fr
†Dedicated to the memory of our mentor, colleague and friend Professor Alessandro Degl’Innocenti.
‡Present address: Laboratoire Chimie Organique Bioorganique Réactivité et Analyses (COBRA), Université et INSA de
Rouen, UMR CNRS 6014, IRCOF, F-76821 Mont Saint Aignan Cedex, France.
© 2013 Taylor & Francis

Journal of Sulfur Chemistry 693
We reported several years ago preliminary results on the synthesis (7) and some properties
(8) of unprecedented 2,6-bis(trialkysilyl)-4H-thiopyrans. These compounds were obtained from
the corresponding 1,5-bis(trialkylsilyl)pentan-1,5-diones by a two-step one-pot procedure, Co(II)
catalyzed thionation by hexamethyldisilathiane (HMDST) (9) – cyclocondensation, as depicted
in Scheme 1 for the bis(t-butyldimethylsilyl) derivative 1. We report herein the optimization of
the synthesis of 1, its metallation and subsequent nucleophilic reactions.
O
O
HMDST, CoCl2·6H2O
CH3CN
+
TBS
TBS
TBS
S
TBS
TBS
O
TBS
2 (minor)
1
Scheme 1. Synthesis of 2,6-bis(t-butyldimethylsilyl)-4H-thiopyran 1 (7).
2. Results and discussion
2.1. Optimization of the synthesis of 2,6-bis(trialkylsilyl)-4H-thiopyrans
The study of the chemical properties of bis(trialkylsilyl)-4H-pyrans required their synthesis at a
multigram scale. As reported in our preliminary paper (7), a minor amount of bis(trialkyslyl)-
4H-pyran 2 was present as a by-product beside the expected thiopyran analogue. The difficult
separation was a drawback we had to overcome before scaling up the reaction. The occurrence of
4H-pyran may be explained either by the acidic medium due to the presence of Co(II) salt and to
the increasing temperature because of the exothermicity of the reaction. 1,5-Bis(acylsilanes) are
known to give intramolecular reaction in acidic medium or by heating to give 2,6-(trialkylsilyl)-
4H-pyrans (10).
The first attempt to scale up the preparation of 2,6-bis-(t-butyldimethylsilyl)-4H-thiopyran
1 under the preliminary reported conditions allowed the isolation of a considerable amount of
the intermediate dithiolactol type compound 3 (such an intermediate had also been observed in
case of the preparation of the homologous 2,7-bis(trialkylsilyl)-4,5-dihydrothiepine, see (7)). The
intermediate character of 3, which has been isolated and characterized, was corroborated by its
conversion to the corresponding thiopyran by refluxing an acetonitrile solution of 3 under similar
Co(II) salt activation (Scheme 2). The overall synthetic pathway is depicted in Scheme 3, where
compound 3ꢀ, the oxygenated analogue of 3, was also mentioned as a possible intermediate,
although it has not been identified in the crude mixture.
Scheme 2. Transformation of intermediate 3 into 4H-thiopyran 1.
Finally, the synthesis was improved by adding slowly the catalyst to reactants and keeping
the reaction at room temperature for one night. The black material formed during the reaction
was removed by filtration before a further treatment with fresh cobalt catalyst in acetonitrile.
Evaporation and filtration of the residue through a pad of silica using diethyl ether as eluent, gave
compound 1 (yield: 83%) as 97% pure material (contaminated by 3% of 4H-pyran).
Similarly, the bis(trimethylsilyl) derivative 4 was prepared (see Section 4). The yield was lower
(54%) probably because of its higher volatility.

694 T. Nocentini et al.
S
S
X
X
TBS
H
TBS
TBS
[S]
O
O
TBS
TBS
TBS
X = O, S
–H2X
TBS
XH
TBS
S
TBS
S
TBS
1
X = S
X = O
3
3'
Scheme 3. Overall synthetic pathway of 4H-thiopyran 1.
2.2. Stability of 2,6-bis(trialkysilyl)-4H-thiopyrans
Compound 1 was unstable and turned to brown oil when exposed to air. It was stored at −10◦C,
in the dark and under argon after three vacuum-argon cycles. Nevertheless, the material became
brown in about three weeks. A filtration through a pad of silica gel using hexanes as eluant usually
allows to obtain a colorless or pale yellow oil while the brown material stays on the top of the silica
pad. After filtration, enough amount of this brown material was recovered for analysis (elution
with diethylether). The very main component of this material proved to be the oxidation product
5, which was characterized after a further purification by preparative thin layer chromatography
(TLC). A plausible mechanism explaining this oxidation process is depicted in Scheme 4.
·O–O·
TBS
TBS
S
TBS
TBS
S
TBS
TBS
S
TBS
1
O2
TBS
S
TBS
S
O
O
TBSO.
O
5
Scheme 4. Possible mechanism for the formation of compound 5.
2.3. Lithiation and nucleophilic reactions
Treatment of 2,6-substituted-4H-thiopyran with a strong base was expected to give a conjugated
specieswithseveralreactionsites. UsuallyC2andC4areconcernedbysuchreaction.Accordingto
the literature, the regioselectivity depends on both substituents and electrophilic reactant. Unsub-
stituted lithiated 4H-thiopyran reacted selectively with benzylchloride at C4 position (3) whereas
alkylation with cyclohexylbromide led to a 15/85 mixture of C4 and C2 branched compounds (4).
Similarly, aftertreatmentwithNaNH2 ort-BuLi, 2,4,6-triphenyl-4H-thiopyranand-2H-thiopyran
are methylated, benzylated or acylated selectively at C4, whereas deuteration occurred exclusively

Journal of Sulfur Chemistry 695
at C2. In contrast, lithiated 2,6-diphenyl-4H-thiopyran was deuterated selectively at C4. The same
regioselectivity was observed for trimethylsilylation (5).
Thus, the precise prediction of the alkylation of deprotonated 2,6-bis(trialkylsilyl)-4H-
thiopyrans was not obvious and justified this exploratory study. Moreover, although they have
never been mentioned with this type of reaction, products resulting from alkylation at sulfur
could theoretically be expected, as proved the results we are reporting here (vide supra). Such
a reaction would lead to compound which may be considered as sulfur ylide, even if they are
usually presented as thiabenzenes (11). Thiabenzenes are formed from reaction of thiopyrillium
salts with nucleophiles. They are usually unstable at room temperature, and their observation is
favored when the ylide carbon bears a stabilizing group like aryl or carbonyl one. In our case, the
presence of the trialkylsilyl group could play such a role.
n-Butyllithium was used as a base and a variety of electrophilic reactants were investigated.
The lithium salt 1Li was formed instantaneously at 0◦C, giving a deep red solution, a color which
seems to corroborate the contribution of a carbon–sulfur double bond in the canonical forms of
the intermediate anion. The plausible pathways are depicted in Scheme 5.
E
1. n-BuLi
2. E+
1
+
+
TBS
S
E
TBS
TBS
S
TBS
E
TBS
S
TBS
n-BuLi
E+
4
2
Li+
TBS
S
TBS
TBS
S
TBS
TBS
S
TBS
TBS
S
TBS
1Li
Scheme 5. Tandem lithiation of 4H-thiopyran 1 – nucleophilic substitution.
2.3.1. Reaction of lithium salt 1Li with halogenated reagents
The results obtained by reaction of 1Li with halogenated derivatives are summarized in Table 1.
The regioselectivity of the reaction of the lithium salt 1Li with halogenated derivatives depends on
the reactant structure. Methylation and trimethylsilylation occurred exclusively at the 4 position,
giving almost quantitatively compounds 6 and 7, respectively (Table 1: Entries 1 and 2). Similarly,
protonation of 1Li occurred exclusively at C4 on acidic hydrolysis.A mixture of two isomers were
produced from isopropyl-(8a + 8b), benzyl-(9a + 9b), allyl-(10a + 10b) and prenyl bromide
(11a + 11b) (Entries 3–6). The yields are moderate and the 4-substituted-4H-thiopyran is the
major isomer except for allyl derivative where the reaction was quantitative and led to the 2-allyl
thiopyran 10b as the major isomer. This particular behavior could be due to the contribution of a
sigmatropic rearrangement subsequent to either 4-allyl- or S-allyl substituted derivatives.
The product 12 reported in Entry 7 results from the regioselective reaction of 1Li with a
perfluoroketene dithiocetal. This type of compound reacts with various electrophiles according
to an addition–elimination process leading to the substitution of the β fluorine (12).
The reaction between 1Li and hexyl bromide is of particular interest (Scheme 6). Whereas
a thiabenzene type intermediate was simply mentioned as a hypothesis in the allylation case,
S-alkylation proved to contribute to the hexylation products. In addition to the product alkylated
at position 4 (13a) and 2 (13b), a significant amount of the thiabenzene product 13c was detected.
Compound 13c survived to aqueous work up. It was stable enough to be observed via 1H-NMR but
decomposed in CDCl3 solution. The selected nuclear magnetic resonance (NMR) data reported in

696 T. Nocentini et al.
Table 1. Reaction of 1Li with halogenated derivatives.
Entry
R-X
Product(s)
Yield (%)a
98
Me
S
1
Me-I
6
7
TBS
TBS
SiMe3
2
3
Me3Si-Cl
99
50
TBS
S
+
TBS
iPr
TBS
S
S
TBS
TBS
iPr-Br
8a + 8b
9a + 9b
iPr
TBS
TBS
S
TBS
3.7 : 1
Bn
S
+
TBS
4
5
Bn-Br
56
99
Bn
TBS
4.6 : 1
+
TBS
S
S
TBS
TBS
Br
10a + 10b
TBS
TBS
S
S
TBS
1 : 1.8
TBS
SEt
+
Br
TBS
6
7
11a + 11b
39
70
5.8 : 1
F3C
SEt
12
F3C
F
SEt
SEt
TBS
S
TBS
Note: aIsolated yield.
Scheme 6 are consistent with those reported in the literature for thiabenzenes (11h). Separation of
the reaction components over silica gel chromatography gave the C-alkylation products 13a and
13b, whereas 13c was totally converted to the 2H-thiopyran 13d, isomer of the starting material.
This transformation could be explained by a sequential or concerted intramolecular elimination
(Scheme 6).

Journal of Sulfur Chemistry 697
n-Hex
+
+
TBS
S
TBS
TBS
S
TBS
n-Hex
TBS
S
TBS
n-HexBr
13d
47%
13a
13b
1Li
50% (7.3 :1)
5.61 ppm
107.2 ppm
H
H
S
6.68 ppm
H
69.4 ppm
140 ppm
+
n-C4H9
TBS
TBS
H
H
1.96–2.09 ppm
13c
Scheme 6. Reaction of 1Li with n-hexyl bromide.
2.3.2. Reaction of lithium salt 1Li with carbonyl derivatives
Two types of products could be expected from the reaction of the lithium salt 1Li with carbonyl
derivatives. Besides addition via the position 4, reaction at carbon 2 bearing the silyl group could
lead to an addition or a Peterson olefination product. The results obtained from various carbonyl
compounds are summarized in Table 2.
All compounds considered in this study reacted selectively at position 4. Reaction with
pivalaldehyde and benzaldehyde gave the alcohol adducts 14 and 15, respectively, in good to
excellent yields (Entries 1 and 2). With a view to a possible approach to a highly conjugated
compound, terephtalaldehyde was reacted in similar conditions and gave the diol 16 (Entry 3).
Unfortunately, attempts to induce dehydration via mesylation or tosylation failed. A conjugate
addition took place using butenolide as reactant giving the lactone derivative 17 (Entry 4). The
last experiment with benzophenone followed a different pathway (Entry 5). The bis-4H-thiopyran
18 was formed in high yield. The most probable pathway consists in an electron transfer from the
anion to benzophenone, giving a highly stabilized radical which dimerizes (Scheme 7). Similar
coupling was reported for related compounds (13).
2.3.3. Metallation and nucleophilic reactions from tris(trialkylsilyl)-4H-thiopyran 7
Further stabilization of the lithium salt anion by a third trialkysilyl group in the 4 position
prompted us to consider the reactivity of bis(t-butyldimethylsilyl)-4-trimethylsilyl-4H-pyran in
similar conditions. The lithium salt 7Li reacted with benzaldehyde as electrophile, but the reac-
tion did not stop at the addition step. A subsequent Peterson type elimination took place giving
almost quantitative yield of an equimolar mixture of the benzylidene derivatives 19 and 20
(Scheme 8).
As observed with the analogue 1Li, the salt 7Li reacted with n-hexyl bromide according
to a particular pathway, giving the thiabenzene 21 (Scheme 9). The NMR data (reported in
the molecular structure 21) are consistent with reported data for thiabenzene structures with,
in particular, the signal at 64.2 ppm for ylidic carbon 2 (11h). The presence of a third tri-
alkylsilyl group in conjugate position undoubtedly favored the effective formation of 21 and
its stabilization.
It is worth noting that few thiopyran derivatives appeared to be not very stable, turning to black
especially when exposed to the day light at room temperature, leading to unidentified degradation
products.

698 T. Nocentini et al.
Table 2. Reaction of 1Li with carbonyl compounds.
Entry
Carbonyl compound
Product
Yield (%)a
98
HO
t-Bu
1
t-Bu-CHO
14
15
TBS
S
TBS
HO Ph
2
3
Ph-CHO
75
65
TBS
OH
S
TBS
TBS
S
TBS
H
O
O
H
S
TBS
16b
TBS
OH
O
O
O
O
4
5
17
18
53
83
TBS
S
TBS
TBS
TBS
Ph-CO-Ph
S
S
TBS
TBS
Notes: aIsolated yield.
bMixture (1:1) of diastereomers.
O
TBS
1/2
TBS
S
Li+
Ph Ph
S
TBS
S
TBS
TBS
S
TBS
O
Li+
TBS
TBS
1Li
Ph Ph
18
Scheme 7. Possible pathway for the formation of dimer 18.
TMS
Ph
TMS
n-BuLi
TBS
PhCHO
+
7Li
Ph
TBS
S
TBS
S
TBS
99%
1 : 1
S
TBS
7
19
20
Scheme 8. Reaction of 7Li with benzaldehyde.

Journal of Sulfur Chemistry 699
113.3 ppm
6.85 ppm
TMS
H
TMS
H
1. n-BuLi
2.
64.2 ppm
144.0 ppm
n-Hex
TBS
S
TBS
TBS
S
TBS
H
H
7
1.92–2.04 ppm
21
80%
Scheme 9. Reaction of 7Li with n-hexyl bromide.
3. Conclusion
2,6-Bis(trialkylsilyl)-4H-thiopyrans constitute a new and interesting class of sulfur heterocycles.
Their metallation converts them to a nucleophile which behaves most often like classically
substituted 4H-thiopyrans. Thus, simple alkylation reactions proceed at positions 2 and 4 (mainly).
On the other hand, in some cases, the reaction follows a particular way, due to the stabilizing effect
of silicon, as for the easy formation of thiabenzenes, or to its oxophilicity, as for the occurrence
of Peterson process on addition to aldehydes. As expected, this effect is enhanced by the presence
of a third silyl group in position 4. Whereas thiabenzenes are generally the result of addition of a
nucleophile on a pyrilium salt, the 2,6-bis- and 2,4,6-tris(trialkylsilyl) substituted thiopyrans may
be converted into thiabenzene via reaction of their lithium salt with n-hexyl bromide.
4. Experimental section
4.1. General remarks
Reagents and solvents were used without further purification. All reactions were monitored by
TLC with Merck silica gel 60 F254 0.25 mm plates and revealed using ultra violet light. Purifi-
cation of 4H-thiopyran derivatives was carried out using flash silica gel column chromatography
(70–200 μm). The purity of synthetic products was established by NMR spectroscopic data and
mass spectra (MS) analysis. 1H and 13C NMR spectra were recorded with a Bruker AC-250 spec-
trometer, in deuteriochloroform if not mentioned. Chemical shifts are reported as δ in units of
parts per million (ppm) relative to internal standards: tetramethylsilane (δ 0.00 ppm) or chloro-
form (δ 7.27 ppm) for 1H, 77.0 ppm (central line) for 13C NMR spectra. Coupling constants are
reported in Hertz (Hz), multiplicities are as follows: s, singlet; d, doublet; t, triplet; q, quartet;
m, multiplet; br, broaded. Low resolution MS were obtained with a mass spectrometer coupled
with gas chromatography (GC-MS) Thermoquest Trace GC 2000 series, in electronic impact (EI)
mode. High resolution mass spectra (HRMS) were recorded on a Q-TOF Micromass spectrometer
in positive electrospray mode (ES+, EC 30V).
4.2. Typical procedure for the synthesis of 2,6-bis(t-butyldimethylsilyl)-4H-thiopyran (1)
To a solution of 1,5-bis(t-butyldimethylsilyl)pentan-1,5-dione (4.34 g, 13.2 mmol) in CH3CN
(35 mL) cooled at 0◦C, were added HMDST (11.2 mL, 52.8 mmol) and a solution of CoCl2·6H2O
(6.3 g, 26.4 mmol) in CH3CN (97 mL), under a N2 atmosphere. The reaction mixture was stirred
overnight at room temperature, then the solvent was evaporated and the residual material was
filtered through a pad of silica gel using diethyl ether as eluant. The filtrate was evaporated,
giving a pale yellow oil which was dissolved in CH3CN (14 mL). After addition of CoCl2·6H2O

700 T. Nocentini et al.
(1.4 g, 5.8 mmol), the solution was heated at reflux for 3 h. The solvent was evaporated and the
resulting mixture was filtered through a pad of silica gel using diethyl ether as eluent. The filtrate
was evaporated and the residue was purified by flash chromatography (eluent: hexanes) affording
4H-thiopyran 1 (3.58 g, 83%, 97% pure) as a colorless oil which slowly crystallized at 20◦C.
2,6-Bis(t-butyldimethylsilyl)-4H-thiopyran (1): this compound has been described in Ref (7).
4.2.1. 2,6-Bis-(t-butyldimethylsilyl)-3,4-dihydro-2H-thiopyran-2-thiol (3)
This compound was isolated (flash chromatography, hexanes, Rf: 0.5) as a colorless oil in 20%
1
yield from a preliminary experiment stopped before the additional CoCl2 treatment. H-NMR
(CDCl3): δ = 0.08 (3H, s), 0.09 (3H, s), 0.17 (3H, s), 0.20 (3H, s), 0.90 (9H, s), 1.06 (9H, s),
1.94–2.26 (3H, m), 2.29 (1H, s), 2.63 (1H, dddd, J = 18.3, 11.4, 5.9, 2.5 Hz), 6.07 (1H, dd,
J = 8.5, 2.7 Hz). 13C-NMR (CDCl3): δ = −7.3 (CH3), −7.2 (CH3), −6.6 (CH3), −6.2 (CH3),
17.2 (Cq), 19.5 (Cq), 20.2 (CH2), 26.8 (CH3), 28.5 (CH3), 32.0 (CH2), 39.5 (Cq), 128.4 (CH),
129.2 (Cq). MS (EI): m/z 360 (M+, 1), 326 (M+-H2S, 13), 269 (M+-(t-Bu), 51), 73 (100). HRMS
(ES+): calcd for C17H37S2Si2 (M+ + H) m/z 361.1875, found: 361.1868.
4.3. Typical optimized procedure for the synthesis of 2,6-bis(trimethylsilyl)-4H-thiopyran (4)
To a solution of 1,5-bis(trimethylsilyl)pentan-1,5-dione (1.00 g, 4.1 mmol) in CH3CN (11 mL)
cooled at 0◦C, were added under a N2 atmosphere HMDST (3.5 mL, 16.5 mmol) and a solution of
CoCl2·6H2O (2.00 g, 8.2 mmol) in CH3CN (30 mL). The reaction mixture was stirred overnight at
room temperature, then the solvent was evaporated and the residual material was filtered through
a pad of silica gel using diethyl ether as eluant. The filtrate was evaporated to give a yellow pale
oil. Flash chromatography (hexanes, Rf: 0.85) afforded 536 mg (54%) of 4 as a colorless oil. 1H-
NMR (CDCl3): δ = 0.15 (18H, s), 2.68 (2H, t, J = 4.5 Hz), 6.01 (2H, t, J = 4.5 Hz). 13C-NMR
(CDCl3): δ = −1.7 (CH3), 29 (CH2), 128 (CH), 137 (Cq). MS (EI): m/z 241 (M+ − 1, 85), 227
(M+ − 15, 49), 169 (M+-SiMe3, 34), 154 (M+-SiMe3-15, 76), 73 (100). HRMS (ES+): calcd for
C11H23SSi2 (M+ + H) m/z 243.1059, found 243.1048.
4.4. 6-(t-Butyldimethylsilyl)-thiopyran-2-one (5)
Filtration on silica gel (eluent: diethylether). 1H-NMR (CDCl3): δ = 0.28 (6H, s), 0.92 (9H, s),
6.47 (1H, d, J = 10.4 Hz), 6.96 (1H, d, J = 7.1 Hz), 7.35 (1H, dd, J = 10.4, 7.1 Hz). 13C-NMR
(CDCl3): δ = −6.3 (CH3), 17.0 (Cq), 26.3 (CH3), 124.5 (CH), 125.2 (CH), 139.9 (CH), 155.9
(Cq), 186.5 (Cq). IR (neat): 1731, 1644 cm−1. MS (EI): m/z 226 (M+, 24), 169 (M+-(t-Bu), 99),
141 (100). HRMS (ES+): calcd for C11H19OSSi (M++H) m/z 227.0926, found 227.0925.
4.5. Typical procedure for the reaction of lithium salt 1Li with electrophilic reagent
To a 0◦C cooled solution of 4H-thiopyran 1 (102 mg, 0.31 mmol) in tetrahydrofuran (THF) (2 mL)
was added n-BuLi (0.37 mmol), 1.2 equivalent of a 2.5 M solution in hexane). The deeply red
colored solution was stirred for 0.5 h at 0◦C then a solution (53 mg, 0.37 mmol) of MeI in THF
(1 mL) was added. The deep red color disappeared at the end of the addition, and the resulting
yellow solution was stirred for 10 min. at 0◦C and for 0.5 h at room temperature. Water (2 mL)
was then added. The solution was extracted three times with diethyl ether (3 × 10 mL) and the
organic layers were dried over MgSO4 and evaporated. The residue was purified by silica gel
column chromatography or preparative TLC.

Journal of Sulfur Chemistry 701
4.5.1. 2,6-Bis-(t-butyldimethylsilyl)-4-methyl-4H-thiopyran (6)
1
Filtration on silica gel (eluent: hexanes, Rf: 0.85). Yield: 98% (122 mg). H-NMR (CDCl3):
δ = 0.13 (6H, s), 0.14 (6H, s), 0.90 (18H, s), 1.30 (3H, d, J = 7.2 Hz), 2.35–2.41 (1H, m), 5.81
(2H, d, J = 3.3 Hz). 13C-NMR (CDCl3): δ = −6.1 (CH3), −5.8 (CH3), 17.0 (Cq), 19.2 (CH3),
26.8 (CH3), 33.5 (CH), 133.3 (Cq), 135.4 (CH). MS (EI): m/z 340 (M+, 4), 325 (100), 73 (64).
HRMS (ES+): calcd for C18H37SSi2 (M+ + H) m/z 341.2154, found: 341.2152.
4.5.2. 2,6-Bis-(t-butyldimethylsilyl)-4-trimethylsilyl-4H-thiopyran (7)
1
Filtration on silica gel (eluent: hexanes, Rf: 0.90). Yield: 99% (198 mg). H-NMR (CDCl3):
δ = 0.11 (12H, s), 0.92 (18H, s), 2.63 (1H, t, J = 6.6 Hz), 5.84 (2H, d, J = 6.6 Hz). 13C-NMR
(CDCl3): δ = −6.01 (CH3), −6.0 (CH3), 17.1 (Cq), 26.8 (CH3), 36.7 (CH), 127.2 (Cq), 131.3
(CH). MS (EI): m/z 398 (M+, 33), 325 (M+-SiMe3, 97), 283 (M+-(t-Bu)Me2, 100), 73 (98).
HRMS (ES+): calcd for C20H43SSi3 (M+ + H) m/z: 399.2393, found 399.2391.
4.5.3. 2,6-Bis-(t-butyldimethylsilyl)-4-isopropyl-4H-thiopyran (8a) and
2,6-bis-(t-butyldimethylsilyl)-2-isopropyl-2H-thiopyran (8b)
Filtration on silica gel (eluent: hexanes, Rf: 0.80). Yield: 50% (45 mg). Mixture (3.7:1) of 8a
1
and 8b. Yellow oil. Compound 8a: H-NMR (CDCl3): δ = 0.10 (12H, s), 0.91 (18H, s), 0.97
(6H, d, J = 6.7 Hz), 1.82–1.98 (1H, m), 2.44 (1H, dt, J = 5.7, 4.4 Hz), 5.90 (2H, d, J = 4.4 Hz).
13C-NMR (CDCl3): δ = −6.0 (CH3), −5.9 (CH3), 17.1 (Cq), 19.9 (CH3), 26.9 (CH3), 31.6 (CH),
44.5 (CH), 132.0 (CH), 132.9 (Cq). MS (EI): m/z 366 (M+-2, 7), 325 (M+-(i-Pr), 100), 73 (31).
Compound 8b: selected data: HRMS (ES+): calcd for C20H41SSi2 (M+ + H) m/z 369.2467,
found: 369.2474.
4.5.4. 4-Benzyl-2,6-bis-(t-butyldimethysilyl)-4H-thiopyran (9a) and
2-Benzyl-2,6-bis-(t-butyldimethysilyl)-2H-thiopyran (9b)
Filtration on silica gel (eluent: hexanes, Rf: 0.8–0.9). Yield: 56% (57 mg). Mixture (4.6:1) of 9a
1
and 9b. Oil. Compound 9a: H-NMR (CDCl3): δ = 0.09 (6H, s), 0.10 (6H, s), 0.88 (18H, s),
2.75–2.82 (2H, m), 2.89–3.00 (1H, m), 5.86 (2H, d, J = 4.3 Hz), 7.12–7.32 (5H, m). 13C-NMR
(CDCl3): δ = −6.0 (CH3), 17.0 (Cq), 26.8 (CH3), 38.7 (CH2), 39.6 (CH), 125.9 (CH), 127.1 (CH),
128.1 (CH), 132.7 (CH), 133.3 (Cq), 139.7 (Cq). MS (EI): m/z 414 (M+-2, 11), 325 (M+-PhCH2,
100), 267 (24), 91 (11), 73 (32). HRMS (ES+) calcd for C24H41SSi2 (M+ + H) m/z 417.2467,
found: 417.2471. Compound 9b: 1H-NMR (CDCl3): δ = −0.01 (6H, s), 0.26 (6H, s), 0.73 (9H,
s), 0.96 (9H, s), 2.76–2.91 (2H, m), 5.24 (1H, d, J = 10.0 Hz), 5.39 (1H, d, J = 5.0 Hz), 5.61
(1H, dd, J = 10.0, 5.0 Hz), 7.00–7.25 (5H, m).
4.5.5. 4-Allyl-2,6-bis-(t-butyldimethylsilyl)-4H-thiopyran (10a) and
2-allyl-2,6-bis-(t-butyldimethylsilyl)-2H-thiopyran (10b)
Filtration on silica gel (eluent: hexanes, Rf: 0.8–0.9).Yield: 99% (89 mg). Mixture (1:1.8) of 10a
1
and 10b. Oil. Compound 10a: H-NMR (CDCl3): δ = 0.12 (12H, s), 0.89 (18H, s), 2.35–2.40
(2H, m), 2.50–2.59 (1H, m), 5.05 (1H, d, J = 9.6 Hz), 5.07 (1H, d, J = 18.3 Hz), 5.77–5.91 (1H,
m), 5.86 (2H, J = 3.6 Hz). 13C-NMR (CDCl3): δ = −6.0 (CH3), −5.9 (CH3), 17.0 (Cq), 26.7
(CH3), 37.7 (CH2), 37.9 (CH), 116.4 (CH2), 133.1 (CH), 133.6 (Cq), 136.2 (CH). MS (EI): m/z
366 (M+, 2), 351 (M+-Me, 3), 325 (100), 73 (48). Compound 10b: 1H-NMR (CDCl3): δ = 0.09

702 T. Nocentini et al.
(6H, s), 0.11 (3H, s), 0.15 (3H, s), 0.93 (9H, s), 1.02 (9H, s), 2.26–2.46 (2H, m), 5.04–5.07 (2H,
m), 5.32 (1H, d, J = 10.3 Hz), 5.80–5.86 (1H, m), 5.96–5.99 (1H, m), 6.06–6.23 (1H, m). 13C-
NMR (CDCl3): δ = −6.9 (CH3), −6.7 (CH3), −6.6 (CH3), −6.1 (CH3), 17.3 (Cq), 19.3 (Cq),
26.8 (CH3), 28.5 (CH3), 34.9 (Cq), 43.5 (CH2), 116.6 (CH2), 123.3 (CH), 123.7 (CH), 126.5 (CH),
133.1 (Cq), 135.6 (CH). MS (EI): m/z 366 (M+, 2), 351 (M+-Me, 3), 325 (100), 73 (48). HRMS
(ES+) calcd for C20H39SSi2 (M+ + H) m/z 367.2311, found 367.2310.
4.5.6. 2,6-Bis-(t-butyldimethylsilyl)-4-(3-methyl-but-2-enyl)-4H-thiopyran (11a) and
2,6-bis-(t-butyldimethylsilyl)-2-(3-methyl-but-2-enyl)-2H-thiopyran (11b)
Filtration on silica gel (eluent: hexanes, Rf: 0.8–0.9).Yield: 39% (22 mg). Mixture (5.8:1) of 11a
and 11b. Oil. Compound 11a: 1H-NMR (CDCl3): δ = 0.12 (12H, s), 0.90 (18H, s), 1.63 (3H, s),
1.71 (3H, s), 2.27–2.32 (2H, m), 2.48–2.54 (1H, m), 5.15–5.25 (1H, m), 5.85 (2H, d, J = 3.7 Hz).
13C-NMR (CDCl3): δ = −6.1 (CH3), −5.9 (CH3), 17.0 (Cq), 18.0 (CH3), 25.8 (CH3), 26.7 (CH3),
32.0 (CH2), 38.6 (CH), 122.1 (CH), 133.1 (Cq), 133.6 (CH), 133.6 (Cq). MS (EI): m/z 392 (M+-2,
6), 325 (100), 73 (43). Compound 11b: 1H-NMR (CDCl3): δ = 0.02 (6H, s), 0.22 (6H, s), 0.70
(9H, s), 0.95 (9H, s), 1.46 (3H, s), 1.48 (3H, s), 2.10–2.40 (2H, m), 5.20 (1H, d, J = 10 Hz), 5.41
(1H, m), 5.68 (1H, dd, J = 10, 5 Hz), 5.86 (1H, d, J = 5 Hz). HRMS (ES+) calcd for C22H43SSi2
(M+ + H) m/z 395.2624, found 395.2619.
4.5.7. 4-(2,2-Bis-ethylsulfanyl-1-trifluoromethyl-vinyl)-2,6-bis-(t-butyldimethyl-silyl)-4H-
thiopyran (12)
Filtration on silica gel (eluent: hexanes). Yield: 70% (38 mg). Oil. 1H-NMR (CDCl3): δ = 0.13
(6H, s), 0.16 (6H, s), 0.91 (18H, s), 1.21 (3H, t, J = 7.4 Hz), 1.29 (3H, t, J = 7.3 Hz), 2.79–2.94
(4H, m), 4.18 (1H, brs), 5.72 (2H, brs). 13C-NMR (CDCl3): δ = −6.2 (CH3), −5.6 (CH3), 14.6
(CH3), 14.8 (CH3), 17.1, (Cq), 26.7 (CH3), 28.2 (CH2), 28.7 (CH2), 45.1 (CH), 123.5 (CF3, q,
1J = 276 Hz), 131.3 (CH), 131.9 (Cq), 137.7 (Cq, q, 2J = 26 Hz), 144.1 (Cq). 19F-NMR (CDCl3):
δ = −53.0 (s). MS (EI): m/z 539 (M+-1, 1), 511 (M+-Et, 3), 449 (100). HRMS (ES+) calcd for
C24H44F3S3Si2 (M+ + H) m/z 541.2096, found 541.2090.
4.5.8. 2,6-Bis-(t-butyldimethylsilyl)-4-hexyl-4H-thiopyran (13a),
2,6-bis-(t-butyldimethyl-silyl)-2-hexyl-2H-thiopyran (13b), and
2,6-bis-(t-butyldimethylsilyl)-2H-thiopyran (13d)
Filtration on silica gel (eluent: hexanes, Rf: 0.85) leading to 50% (31 mg) of a mixture (7.3:1) of
1
13a and 13b (oil) and 47% (23 mg) of 2H-thiopyran 13d. Compound 13a: H-NMR (CDCl3):
δ = 0.13 (12H, s), 0.83–0.91 (3H, m), 0.90 (18H, s), 1.06–1.62 (10H, m), 2.39–2.48 (1H, m), 5.87
(2H, d, J = 3.9 Hz). 13C-NMR (CDCl3): δ = −6.0 (CH3), −5.8 (CH3), 14.1 (CH3), 17.0 (Cq),
22.6 (CH2), 26.8 (CH3), 26.9 (CH2), 29.5 (CH2), 31.8 (CH2), 33.4 (CH2), 38.6 (CH), 133.0 (Cq),
134.0 (CH). MS (EI): m/z 409 (M+-1, 4), 351, (8), 325 (100), 73 (39). Compound 13b: 1H-NMR
(CDCl3): δ = 0.11 (6H, s), 0.16 (6H, s), 0.88 (9H, s), 0.92 (9H, s), 0.85–0.90 (3H, m), 1.21–
2.04 (10H, m), 5.36 (1H, dd, J = 7.5, 5.0 Hz), 5.87 (1H, d, J = 7.5 Hz), 6.14 (1H, d, J = 5.0 Hz).
HRMS (ES+) calcd for C23H47SSi2 (M++H) m/z 411.2937, found 411.2942. Compound 13d: oil.
1H-NMR (CDCl3): δ = 0.10 (6H, s), 0.14 (6H, s), 0.95 (18H, s), 2.72 (1H, dd, J = 5.3, 2.0 Hz),
5.50 (1H, dd, J = 9.7, 5.3 Hz), 5.93 (1H, ddd, J = 9.7, 5.6, 2.0 Hz), 6.26 (1H, d, J = 5.6 Hz).
13C-NMR (CDCl3): δ = −7.2 (CH3), −7.0 (CH3), −6.2 (CH3), −5.9 (CH3), 17.0 (Cq), 17.5 (Cq),
26.8 (CH3), 27.1 (CH3), 41.4 (CH), 118.8 (CH), 125.8 (CH), 130.5 (CH), 134.0 (Cq), 136.1 (Cq).
MS (EI): m/z 326 (M+, 22), 269 (M+-(t-Bu), 7), 211 (100), 73 (75).

Journal of Sulfur Chemistry 703
4.5.9. [2,6-Bis-(t-butyldimethylsilyl)-4H-thiopyran-4-yl]-phenylmethanol (14)
Filtration on silica gel (eluent: hexanes). Yield: 98%. Oil. 1H-NMR (CDCl3): δ = 0.06 (3H, s),
0.10 (3H, s), 0.15 (6H, s), 0.88 (9H, s), 0.92 (9H, s), 2.13 (1H, brs), 3.20–3.26 (1H, m), 4.74 (1H,
d, J = 7.3 Hz), 5.64 (1H, d, J = 5.2 Hz), 6.02 (1H, d, J = 5.2 Hz), 7.27–7.37 (5H, m). 13C-NMR
(CDCl3): δ = −6.1 (CH3), −6.0 (CH3), −5.9 (CH3), 17.0 (Cq), 26.8 (CH3), 45.7 (CH), 74.7 (CH),
126.6 (CH), 127.5 (CH), 128.1 (CH), 128.8 (CH), 129.3 (CH), 134.7 (Cq), 135.0 (Cq), 142.2 (Cq).
HRMS (ES+) calcd for C42H75O2S2Si4 (M+ + H) m/z 787.4286, found: 787.4276.
4.5.10. 1-[2,6-Bis-(t-butyldimethylsilyl)-4H-thiopyran-4-yl]-2,2-dimethyl-propan-
1-ol (15)
Filtration on silica gel (eluent: hexanes). Yield: 75%. Oil. H-NMR (CDCl3): δ = 0.14 (12H, s),
0.90 (9H, s), 0.91 (9H, s), 0.98 (9H, s), 1.79 (1H, brs), 2.88–2.93 (1H, m), 3.4–3.49 (1H, brs), 5.93
(1H, d, J = 5.0 Hz), 6.05 (1H, d, J = 5.0 Hz). 13C-NMR (CDCl3): δ = −5.9 (CH3), −5.8(CH3),
17.0 (Cq), 26.8 (CH3), 26.9 (CH3), 35.7 (Cq), 41.4 (CH), 81.7 (CH), 129.7 (CH), 133.0 (CH),
134.5 (Cq), 135.8 (Cq). HRMS (ES+) calcd for C22H45OSSi2 (M+ + H) m/z 413.2730, found
413.2733.
4.5.11. [2,6-Bis-(t-butyldimethylsilyl)-4H-thiopyran-4-yl]-(4-{[2,6-bis-(t-butyldimethylsilyl)-
4H-thiopyran-4-yl]-hydroxymethyl}-phenyl)-methanol (16)
1
Filtration on silica gel (eluent: hexanes). Yield: 65%. Mixture (1:1) of diastereomers. Oil. H-
NMR (CDCl3): δ = 0.05 (6H, s), 0.06 (6H, s), 0.09 (6H, s), 0.10 (6H, s), 0.14 (12H, s), 0.15 (12H,
s), 0.87 (18H, s), 0.88 (18H, s), 0.91 (18H, s), 0.92 (18H, s), 2.17 (4H, brs), 3.18–3.27 (4H, m),
4.71–4.77 (4H, m), 5.60 (2H, d, J = 5.4 Hz), 5.68 (2H, d, J = 5.1 Hz), 5.97 (2H, d, J = 5.1 Hz),
6.04 (2H, d, J = 5.4 Hz), 7.30 (4H, s), 7.31 (4H, s). 13C-NMR (CDCl3): δ = −6.1 (CH3), −5.9
(CH3), 17.0 (Cq), 26.7 (CH3), 45.7 (CH), 45.8 (CH), 74.2 (CH), 74.6 (CH), 126.3 (CH), 126.4
(CH), 128.5 (CH), 128.7 (CH), 129.3, (CH), 129.3 (CH), 134.6 (Cq), 134.8 (Cq), 135.1 (Cq), 135.1
(Cq), 141.5 (Cq), 141.6 (Cq). HRMS (ES+) calcd for C42H75O2S2Si4 (M+ + H) m/z 787.4286,
found: 787.4276.
4.5.12. [4-[2,6-Bis-(t-butyldimethylsilyl)-4H-thiopyran-4-yl]-dihydrofuran-2-one (17)
Filtration on silica gel (eluent: hexanes). Yield: 53%. Oil. 1H-NMR (CDCl3): δ = 0.13 (6H, s),
0.14 (6H, s), 0.89 (18H, s), 2.42 (1H, dd, J = 17.5, 7.6 Hz), 2.54 (1H, dd, J = 17.5, 8.2 Hz),
2.75–2.90 (1H, m), 2.96 (1H, dt, J = 7.9, 5.4 Hz), 4.19 (1H, dd, J = 9.2, 6.6 Hz), 4.34 (1H, dd,
J = 9.2, 7.3 Hz), 5.85 (2H, d, J = 5.4 Hz). 13C-NMR (CDCl3): δ = −6.2 (CH3), −6.0 (CH3),
16.9 (Cq), 26.7 (CH3), 32.0 (CH2), 38.1 (CH), 39.5 (CH), 71.3 (CH2), 127.9 (CH), 128.0 (CH),
136.2 (Cq), 136.4 (Cq), 176.9 (Cq). MS (EI): m/z 325 (100), 269 (40), 211 (23), 73 (89).
4.5.13. 2,6,2ꢀ,6ꢀ-Tetrakis-(t-butyldimethylsilyl)-4H,4ꢀH-[4,4ꢀ]bithiopyranyl (18)
1
Filtration on silica gel (eluent: hexanes). Yield: 83%. Oil. H-NMR (CDCl3): δ = 0.11 (12H,
s), 0.12 (12H, s), 0.89 (36H, s), 3.03 (2H, t, J = 2.5 Hz), 5.92 (4H, d, J = 2.5 Hz). 13C-NMR
(CDCl3): δ = −6.2 (CH3), −5.9 (CH3), 17.0 (Cq), 26.7 (CH3), 41.4 (CH), 131.5 (CH), 134.0
(Cq). HRMS (ES+) calcd for C34H67S2Si4 (M+ + H) m/z 651.3761, found 651.3741.

704 T. Nocentini et al.
4.5.14. 2-Benzylidene-6-(t-butyldimethylsilyl)-4-trimethylsilyl-2H-thiopyran (19) and
4-Benzylidene-2,6-bis-(t-butyldimethylsilyl)-4H-thiopyran (20)
Purification by preparative TLC on silica gel (eluent: hexanes, Rf: 0.4). Yield: 99% (71 mg).
Mixture (1:1) of 19 and 20. Oil. GC-MS (EI): compound 19 m/z 372 (M+, 36), 73 (100);
compound 20 m/z 414 (M+, 48), 73 (100). 13C-NMR (CDCl3) of 19 + 20: δ = −6.5 (CH3),
−6.4 (CH3), −2.2 (CH3), 17.2 (Cq), 17.3 (Cq), 26.6 (CH3), 26.7 (CH3), 119.4 (CH), 120.6 (CH),
125.4 (CH), 125.8 (CH), 127.6 (CH), 127.7 (CH), 128.1 (CH), 128.2 (CH), 128.7 (CH), 129.2
(CH), 129.4 (Cq), 130.8 (Cq), 131.3 (CH), 133.3 (Cq), 133.5 (Cq), 135.6 (CH), 136.5 (Cq), 137.2
(Cq), 138.0 (Cq).
4.5.15. 2,6-Bis-(t-butyldimethylsilyl)-1-hexyl-4-trimethylsilyl-4H-thiopyran (21)
1
Purification by preparative TLC on silica gel (eluent: hexanes, Rf: 0.54).Yield: 80%. Oil. H-
NMR (CDCl3): δ = −0.04 (9H, s), 0.00 (6H, s), 0.10 (6H, s), 0.75 (18H, s), 0.85–0.90 (3H, m),
1.15–1.50 (10H, m), 1.92–2.03 (2H, m), 6.85 (2H, s). 13C-NMR (CDCl3): δ = −5.0 (CH3), −4.9
(CH3), −0.6 (CH3), 14.0 (CH3), 17.8 (Cq), 22.4 (CH2), 26.7 (CH2), 28.1 (CH2), 31.3 (CH2), 37.6
(CH2), 64.2 (Cq), 113.3 (Cq), 144.0. MS (EI): m/z 483 (M+, 18), 73 (100).
Acknowledgements
A particular and sincere recognition to Prof. Alessandro Degl’Innocenti for his scientific contribution to this research. We
also thank the European commission for financial support (Marie-Curie Training Site (CP group) and a fellowship (TN)).
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