Fluorination of α-phenylsulfanyl esters using difluoroiodotoluene

Article abstract of DOI:10.1039/b209079a

Treatment of α-phenylsulfanyl esters 11-14 with one equivalent of difluoroiodotoluene 3a produced the α-fluoro sulfides 17-20 in good overall yield through a Fluoro-Pummerer reaction. A second equivalent of reagent produced α,α-difluoro sulfides and a third led to α,α-difluoro sulfoxides. An identical pattern of reactivity was observed with the α-phenylsulfanyl lactone 26. This sequential fluorination-oxidation behaviour was exploited in the one-pot synthesis of 3-fluoro-2(5H)-furanone 33 starting from α-phenylsulfanylbutyrolactone 32.

Full text of DOI:10.1039/b209079a

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Fluorination of ꢀ-phenylsulfanyl esters using difluoroiodotoluene
William B. Motherwell,* Michael F. Greaney† and Derek A. Tocher
Department of Chemistry, Christopher Ingold Laboratories, University College London,
20 Gordon Street, London, UK WC1H OAJ. E-mail: w.b.motherwell@ucl.ac.uk;
Fax: 44 20 7679 7524; Tel: 44 20 767 97533
1
Received (in Cambridge, UK) 18th September 2002, Accepted 6th November 2002
First published as an Advance Article on the web 22nd November 2002
Treatment of α-phenylsulfanyl esters 11–14 with one equivalent of difluoroiodotoluene 3a produced the α-fluoro
sulfides 17–20 in good overall yield through a Fluoro-Pummerer reaction. A second equivalent of reagent produced
α,α-difluoro sulfides and a third led to α,α-difluoro sulfoxides. An identical pattern of reactivity was observed with
the α-phenylsulfanyl lactone 26. This sequential fluorination–oxidation behaviour was exploited in the one-pot
synthesis of 3-fluoro-2(5H )-furanone 33 starting from α-phenylsulfanylbutyrolactone 32.
solids, consequently these two reagents have subsequently been
used in all of our fluorination work.
Introduction
The importance of selectively fluorinated compounds in
medicinal chemistry has provided a strong incentive for the
discovery of new fluorinating reagents which can operate in an
efficient, safe and mild manner. In consequence, the controlled
introduction of one or more fluorine atoms into organic
molecules continues to present a worthwhile challenge for
modern synthetic methods.1 Within this area, our own interest
has centred around an exploration of fluorinating agents based
on the hypervalent iodoarene difluoride structure 3. These
venerable compounds have seen only sporadic2 use in fluorin-
ation until recently, when we,3–9 and others,10–16 have examined
them in the context of mild and convenient reagents for the
formation of the carbon–fluorine bond.
Hypervalent iodine() difluorides were first synthesised by
Stille in 1901,17 and several procedures have since been
described for their preparation.18 For our own studies, we have
found that the best method is that of Carpenter, involving
halogen exchange of the congeneric iodine() dichloride. This
protocol provides a safe, reproducible and experimentally
convenient procedure for laboratory use and the simple
two-step operation is readily adapted to a multi-gram scale
(Scheme 1).19
Our earlier studies established that the electrophilic hyper-
valent iodine difluorides have a particular affinity for nucleo-
philic sulfur-containing compounds, and this observation has
been exploited in the fluorination of dithioketals,4 arylthio-
glycosides,5 xanthate esters6 and, most recently a variety of
α-acylsulfides.7–9 Two principal mechanisms can be considered
for the introduction of fluorine into sulfides using 3 (Scheme 2).
Firstly, substrates preferably possessing a geminal heteroatom
such as 4 are fluorinated with cleavage of the carbon–sulfur
bond. The electrophilic iodine reagent is first attacked by
nucleophilic sulfur to give an adduct such as 5, the ligand
exchange at iodine resulting in the displacement of fluoride.
The activated sulfur-species is then displaced by nucleophilic
fluoride, often with participation from the neighbouring hetero-
atom, to produce fluorides 6.
By way of contrast, the second pathway which can operate
does not involve cleavage of the carbon–sulfur bond, and is
analogous to the classical Pummerer reaction. In this instance,
sulfides such as 7 containing an electron-withdrawing group in
the α-position are activated by 3 to form adducts 8, which are
sufficiently acidic to undergo deprotonation with basic fluoride.
The resulting sulfonium species 9 may then be trapped with
fluoride to produce the α-substituted products 10. In mech-
anistic terms, the hypervalent iodoarene difluorides do bear
some similarity to the widely used fluorinating agent DAST,20
inasmuch as both are inherently electrophilic in character and
function in the first instance to create both an activated leaving
group and also to provide a source of nucleophilic fluoride for
nucleophilic displacement. The significant difference however is
that whilst DAST is primarily oxophilic, reagents 3 exhibit
thiophilic character.
Scheme 1
In this and the following paper we discuss, in full detail,
the fluorination of a range of sulfides which illustrate both
of the Type 1 and 2 pathways. The present paper focuses on
α-phenylsulfanyl esters, a class of substrates that effectively
undergo Fluoro-Pummerer (Type 2) reaction with DFIT 3a to
give α-fluoro sulfides.
Thus, the iodoarene 1 is first treated with chlorine gas to form
the aryliodine dichloride 2, and then transhalogenated with
aqueous hydrofluoric acid in the presence of mercuric oxide to
yield the iodine difluoride 3. We were initially concerned over
the stability of 3, as previous workers had used these com-
pounds as DCM solutions, being concerned about possible
decomposition in the solid state.2e,f,19 However, we have found
that the crystalline p-Me (difluoroiodotoluene, DFIT, 3a) and
p-But (3b) derivatives could be easily manipulated and stored as
Results and discussion
The α-fluorination of sulfoxides or sulfides through the Fluoro-
Pummerer reaction is known as an effective strategy for the
synthesis of α-fluoro sulfides and a number of reagents have
been shown to effect this transformation.21 The α-fluoro sulfides
† Current address: School of Chemistry, University of Edinburgh,
King’s Buildings, West Mains Rd, Edinburgh, UK EH9 3JJ
DOI: 10.1039/b209079a
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This journal is © The Royal Society of Chemistry 2002
2809

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Scheme 2
synthesised in this manner have found application as enzyme
inhibitors,22 as 19F NMR structural probes in proteins23 and as
synthons for vinyl fluorides.24 We were particularly interested in
examining the fluorination of α-phenylsulfanyl esters in light of
a report by Fuchigami on the fluorination of ethyl (arylsulfanyl)-
acetates with electrogenerated difluoroiodoarenes in the
presence of Et3Nؒ3HF.16 In that system reactions were found
to be incomplete, necessitating two equivalents of fluorinating
agent and the product fluorides were isolated in moderate yields
(<50%). Our results using difluoroiodotoluene (DFIT, 3a)
in the Fluoro-Pummerer reaction of some α-phenylsulfanyl-
acetates are shown in Table 1.
Examination of the results (Entries 1–4) shows that the
expected α-fluoro sulfides were formed cleanly and in good
overall yields upon treatment with only one single equivalent of
DFIT in DCM. It was also of interest to note (Entries 2 and 3)
that capture of the Pummerer intermediate by fluoride anion
was faster than cyclisation to give a γ-lactone by π-partici-
pation, even when a tertiary or benzylic carbocation could be
formed. It is therefore interesting to speculate that capture of
fluoride from the Pummerer intermediate might possibly occur
via a “reductive elimination” or SNi sequence as shown in Fig. 1.
α,α-difluorosulfoxide 22 was also worthy of note and suggested
possible applications to the synthesis of vinyl fluorides (vide
infra). The thiochromanyl derivative 16 (Entry 7) was excep-
tional in being unproductive in the Fluoro-Pummerer reaction,
decomposing to a number of unidentified products when
treated with DFIT. The presence of an additional sulfur atom
in the substrate may be important in this regard, offering an
extra coordination site to the reagent.
In order to gain further insight into the nature of the
surrounding environment when ester functionality is used as the
electron withdrawing group we were therefore interested in
extending the Fluoro-Pummerer chemistry of aryl iodine
difluorides to more complex systems. The Pummerer reaction is
of broad scope, especially when applied to sulfoxides having
both α and β hydrogens.25 In such systems the formation of the
α,β-unsaturated sulfide 25, arising from β-elimination in the
acylsulfonium intermediate 23 is frequently competitive with
the α-substitution product 24 (Scheme 3).26
Fig. 1
Most significantly, and in contrast to DAST, a second
fluorination was also possible with the α,α-difluorosulfide 21
(Entry 5) being formed on treatment of the ethyl derivative 15
with two equivalents of DFIT. Two sequential Fluoro-
Pummerer reactions have been found to be problematic with
the widely-employed fluorinating agent DAST.21b The find-
ing that addition of a third equivalent (Entry 6) led to the
Scheme 3
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J. Chem. Soc., Perkin Trans. 1, 2002, 2809–2815

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Table 1 Fluorination of α-phenylsulfanyl acetates with DFITa
Entry
Ester
Product
Yield (%)b
1
11
12
13
14
17
18
19
20c
72
2
3
4
67
64
53
5
15d
21
22
80
6
7
15e
16
38
0
–
a Method: DFIT (1 eq.), DCM, 0 ЊC, stirring overnight. b Isolated yields. c Isolated as a 1:1 mixture of diastereoisomers. d 2 eq. DFIT. e 3 eq. DFIT,
19% of 21 also isolated
The racemic lactone 26 was accordingly prepared with a view
to examining whether the presence of β hydrogens would lead
to alternative products in the Fluoro-Pummerer reaction with
DFIT.
In the event, treatment of 26 with one equivalent of DFIT
gave the α-fluoro sulfide 27 as a single diastereoisomer in 62%
yield as the only isolated product. The X-ray structure of 27
shows the fluoride to have been introduced syn to the bulky
phenyl group in the 5-position. The phenylsulfanyl group
occupies a pseudoaxial position and the phenyl group is
disposed pseudoequatorially, a consequence of the longer C–S
bond relative to the C–C bond (Scheme 4).
classical Pummerer reactions has been reported, and is believed
to be due to a highly concerted transition state involving simul-
taneous deprotonation and nucleophilic attack.28 Although
detailed mechanistic studies have yet to be carried out, a similar
mechanism may be operating here. Scheme 5 shows the Pum-
merer adduct 28, formed from DFIT addition to 27, being
deprotonated by fluoride from the α-face necessitating intra-
molecular delivery of fluoride from the β-face through the
highly synchronous transition state 29.
Scheme 5
As expected, the use of a second equivalent of DFIT pro-
duced the fluoro-sulfoxide 30, in analogy to the fluorination of
the acyclic ester 15 (Scheme 6). We recognised this result to have
a significant bearing on our interest in the synthesis of vinyl
fluorides as α-fluoro sulfoxides may be converted to these com-
pounds through pyrolytic elimination of sulfenic acid. Accord-
ingly, heating 30 in toluene for 20 min provided the expected 3-
fluoro-2(5H )-furanone derivative 31 in 72% yield. It was found
that isolation of the intermediate α-fluoro sulfoxide was
Scheme 4
Introduction of fluorine syn to the bulky phenyl group was
unexpected, given that electrophilic addition of methyl iodide
to the lithium enolate of 26 is known to give the anti product.27
Nucleophilic addition of acetate to the more hindered face in
J. Chem. Soc., Perkin Trans. 1, 2002, 2809–2815
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multiplet; br, broad. Low resolution mass spectra were recorded
under either electron impact, atmospheric pressure chemical
ionisation, or fast atom bombardment conditions on a VG 305
or a VG ZAB SE mass spectrometer at the School of Pharmacy,
University of London. Only molecular ions, fragments from
molecular ions and other major peaks are reported. High
resolution mass spectra were recorded using a VG 7070b mass
spectrometer at the School of Pharmacy, University of
London.
Difluoroiodotoluene 3a19
Dry chlorine gas was blown over the surface of a stirred
solution of iodotoluene (7.50 g, 35 mmol) in dry PE 40–60
(65 mL) at 0 ЊC in the dark for 1.5 h. After flushing with nitro-
gen for 1 h the mixture was filtered to give dichloroiodotoluene
Scheme 6
1
(9.64 g, 95%) as a yellow solid; mp 62–65 ЊC (decomp.); H
unnecessary. Thus, treatment of 32 with DFIT followed by
aqueous work-up and thermolysis of the crude product in
refluxing toluene gave the 2-fluorobut-2-en-4-olide 33 directly
in 43% yield.
Previous syntheses of these fluorinated synthons have
required an (E)-selective Wittig–Horner reaction of an
aldehyde with a fluorophosphonate followed by hydrolytic
ring-closure.29 Sulfanylation of an appropriate lactone followed
by DFIT treatment, hydrolysis and syn elimination thus
represents a versatile alternative.
NMR (400 MHz, CDCl3): δH 2.48 (3H, s, CH3), 7.28 (2H,
AAЈBBЈ d J 9 Hz, 3-H, 5-H), 8.05 (2H, AAЈBBЈ d J 9 Hz, 2-H,
6-H); MS (APCI): m/z 255 ([M Ϫ 35Cl]ϩ, 30%), 253 ([M Ϫ
37Cl]ϩ, 100), 218 ([C7H7I]ϩ, 65). Dichloroiodotoluene (9.64 g)
was dissolved in DCM (60 mL) in a polypropylene erlenmeyer
flask. Yellow mercuric oxide (9.50 g, 44 mmol) and 48% aq.
hydrofluoric acid (13 mL, 410 mmol) were then added. The
slurry was vigorously shaken periodically over 2 h, then filtered
and the organic layer separated. After swirling with MgO the
solution was decanted and concentrated in vacuo to yield the
title compound 3a (5.87 g, 66%) as a white solid; mp 110 ЊC
(decomp., DCM); IR (thin film/cmϪ1): νmax 1636m, 1395w,
1278w, 1116w, 800s; 1H NMR (400 MHz, CDCl3): δH 2.48 (3H,
s, CH3), 7.40 (2H, AAЈBB d J 8 Hz, 3-H, 5-H), 7.84 (2H,
AAЈBBЈ d J 8 Hz, 2-H, 6-H); 13C NMR (100 MHz, CDCl3): δC
21.2 (CH3), 130.3, 132.2, 137.3, 142.4; 19F NMR (376 MHz,
Conclusions
We have demonstrated that difluoroiodotoluene 3a is an effective
reagent for the α-fluorination of α-phenylsulfanylesters. The
systems investigated fall squarely within the Type 2 reaction
mechanism manifold we have defined, reliably producing the
simple Fluoro-Pummerer products under mild reaction condi-
tions, without the necessity for any further additions of external
fluoride sources or catalysts.
CDCl3): δF Ϫ177.1; MS (EI): m/z 256 (M ϩ, 15%), 218
ؒ
([C7H7I]ϩ, 80), 127 (Iϩ, 7), 91 ([C7H7]ϩ, 100); HRMS (EI) calcd.
for C7H7F2I: 255.9561. Found: 255.9570. In some runs the
DFIT was contaminated with unreacted iodotoluene. The
extent of reaction could be quantified by 1H NMR, and is
indicated as a percentage where appropriate. No percentage
figure indicates pure (1H NMR) difluoroiodotoluene.
Experimental
Diethyl ether and tetrahydrofuran were distilled from sodium
benzophenone ketyl. DCM and chloroform were distilled from
either phosphorus pentoxide or calcium hydride. Toluene and
benzene were distilled over sodium. Methanol was distilled
from magnesium turnings. Triethylamine, pyridine, isopropyl-
amine and acetonitrile were distilled over calcium hydride.
Melting points were determined using a Reichert hot stage
and are uncorrected. Boiling points for Kugelröhr distillations
refer to uncorrected air temperatures. Microanalyses were
performed by Mr Alan Stone and Mrs Jill Maxwell, Christopher
Ingold Building, University College London. Infrared spectra
were recorded as thin films or Nujol mulls on KBr plates, as
KBr discs, or as CCl4 solutions on a Perkin-Elmer FT-IR 1605
instrument. Major features of each spectrum are reported. The
abbreviations used to denote peak intensity are w, weak; m,
medium; s, strong; br, broad. 1H NMR spectra were recorded at
500 MHz on a Bruker Avance 500, at 400 MHz on a Varian
VXR-400 or a Bruker AMX-400 and at 300 MHz on a Bruker
AMX-300 spectrometer. 13C NMR Spectra were recorded at
General procedure for the synthesis of ꢀ-phenylsulfanyl
acetates. Triethylamine or pyridine (1 eq.) was added to a
stirred solution of alcohol (1 eq.) in DCM (ca. 3 mL mmolϪ1).
The mixture was cooled in an ice-salt bath (<0 ЊC) and phenyl-
sulfanylacetyl chloride was added dropwise. Consumption of
starting alcohol was monitored by TLC and the reaction was
quenched with water upon completion. The aqueous phase was
extracted with DCM (×2), the combined extracts dried
(MgSO4) and concentrated in vacuo. Flash chromatography
afforded pure products.
Phenyl (phenylsulfanyl)acetate 11. Colourless oil; Rf 0.65
(SiO2, PE 30–40:ether 80:20); IR (thin film/cmϪ1): νmax 3062m
(CH), 1763s (C᎐O), 1590m, 1488s, 1440w, 1405w, 1252s, 1193s,
᎐
1
1116s, 1024w, 934m, 894m, 742s, 689s; H NMR (500 MHz,
CDCl3): δH 3.88 (2H, s, SCH2), 7.02 (2H, dd J 7, 1 Hz),
7.25–7.54 (6H, m), 7.55 (2H, dd J 7, 1 Hz); 13C NMR (125
MHz, CDCl3): δC 37.4 (SCH2), 121.7, 126.5, 127.8, 129.6, 129.8,
125 MHz, 100 MHz or 75 MHz on the instruments above. 13
C
131.1, 134.8 (SCipso), 151.0 (OCipso), 168.7 (C᎐O); MS (FAB):
NMR spectra assignments are supported by DEPT editing.
Chemical shifts (δ) are quoted in parts per million (ppm) and
are referenced to the residual solvent peak. (2C) Indicates that
the quoted chemical shift refers to two signals separated by less
than 0.05 ppm. 19F NMR Spectra were recorded at 471 MHz,
376 MHz or 282 MHz on the instruments above. Chemical
shifts (δ) are quoted in parts per million (ppm) and are
referenced to CFCl3. Coupling constants are measured in Hertz
and quoted to the nearest Hertz for all spectra. The abbrevi-
ations used to indicate multiplicity are s, singlet; d, doublet; t,
triplet; q, quartet; dd, double doublet; dt, double triplet; m,
᎐
m/z 244 (Mϩ, 100%); HRMS (FAB) calcd. for C14H12O2S:
244.0558. Found 244.0567.
(E )-Cinnamyl (phenylsulfanyl)acetate 12. Green oil; Rf 0.58
(SiO2, PE 30–40:ether 85:15); IR (thin film/cmϪ1): νmax 3058m,
2945m (CH), 1732 (C᎐O), 1583m, 1440s, 1265s, 1141s, 965s,
᎐
742s, 691s; 1H NMR (300 MHz, CDCl3): δH 3.71 (2H, s, SCH2),
trans
4.79 (2H, d J 7 Hz, 1-H), 6.23 (1H, dt
J
16 Hz, 3J2,1 7 Hz
AB
trans
2-H), 6.65 (1H, d
J
16 Hz, 3-H), 7.19–7.47 (10H, m,
AB
Ar–H); 13C NMR (75 MHz, CDCl3): δC 36.7 (SCH2), 66.0
2812
J. Chem. Soc., Perkin Trans. 1, 2002, 2809–2815

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(1-C), 122.5 (2-C), 126.6 (2C), 127.1, 128.1, 128.6, 129.0, 130.1,
1H NMR (300 MHz, CDCl3): δH 6.28 (1H, d 2JHF 51 Hz, 2-H),
134.6, 136.0, 169.5 (C᎐O); MS (FAB): m/z 417 (MCsϩ, 30%),
6.84–7.64 (10H, m, Ar–H); 13C NMR (75 MHz, CDCl3): δC 93.8
᎐
284 (Mϩ, 100); HRMS (FAB) calcd. for C17H16O2S: 284.0871.
Found: 284.0866.
(d JCF 234 Hz, 2-C) 120.9, 126.4, 129.0 (SCipso), 129.3, 129.5,
2
2
129.7, 134.5, 149.8 (OCipso), 163.8 (d JCF 31 Hz, C᎐O); 19F
᎐
NMR (282 MHz, CDCl3): δF Ϫ158.5 (d 2JFH 51 Hz); MS (FAB):
m/z 285 (MNaϩ, 35%), 262 (Mϩ, 100); HRMS (FAB) calcd.
for C14H11FO2S: 262.0464. Found: 262.0459; plus unreacted
starting material (12%).
Prenyl (phenylsulfanyl)acetate 13. Colourless oil; bp 175 ЊC/
0.5 mBar; Rf 0.43 (SiO2, PE 30–40:ether 90:10); IR (thin film/
cmϪ1): νmax 2924m (CH), 1734s (C᎐O), 1440w, 1276m, 1130m,
᎐
959w, 740m, 688m; 1H NMR (300 MHz, CDCl3): δH 1.69 (3H,
s, CH3), 1.76 (3H, s, CH3), 3.66 (2H, s, SCH2), 4.62 (2H, d J 8
Hz, 1-H), 5.30 (1H, m, 2-H), 7.23–7.43 (5H, m, Ar–H); 13C
NMR (100 MHz, CDCl3): δC 18.1 (CH3), 25.8 (CH3), 36.8
(SCH2), 62.4 (1-C), 118.1 (2-C), 126.9, 129.0, 130.0, 135.0,
Cinnamyl (2-fluoro-2-phenylsulfanyl)acetate 18. A solution
of DFIT (80%, 328 mg, 1.1 mmol) and sulfide 12 (300 mg,
1.1 mmol) in DCM (6 mL) was stirred for 2.5 h. Work-up
according to the general procedure followed by flash chroma-
tography (SiO2, PE 30–40:ether 95:5) yielded the fluoride 18
(221 mg, 67%) as a colourless oil; Rf 0.18 (SiO2; PE 30–40:ether
139.9, 169.7 (C᎐O); MS (FAB): m/z 236 (Mϩ, 35%), 123 ([M Ϫ
᎐
PhSCH2]ϩ, 100); Anal. Calcd. for C13H16O2S: C, 66.07; H,
6.82%. Found: C, 65.80; H, 6.58%.
90:10); IR (thin film/cmϪ1): νmax 3028s, 2953s (CH), 1756s
1
(C᎐O), 1441s, 1322s, 1297s, 1175s, 1037s, 967s, 747s, 691s; H
᎐
(3R)-4,5-Dihydro-4,4-dimethyl-3-(phenylsulfanyl)acetoxy-
NMR (300 MHz, CDCl3): δH 4.72–4.76 (2H, m, 1-H), 6.12
2(3H)-furanone 14. Yellow oil; Rf 0.32 (SiO2, PE 30–40:ether
(1H, d 2JHF 52 Hz, SCHF), 6.13 (1H, dt transJ2,3 16 Hz, 3J2,1 7 Hz,
50:50); IR (thin film/cmϪ1): νmax 2967m (CH), 1790s (C᎐O
2-H), 6.63 (1H, d
J
16 Hz, 3-H), 7.27–7.57 (10H, m,
trans
᎐
3,2
lactone), 1747s (C᎐O ester), 1584m, 1470m, 1378m, 1263s,
Ar–H); 13C NMR (100 MHz, CDCl3): δC 66.7 (1-C), 94.11
᎐
1128s, 1079s, 1013m, 743s, 690s; 1H NMR (300 MHz, CDCl3):
δH 1.01 (3H, s, CH3), 1.18 (3H, s, CH3), 3.60–3.77 (2H, m, 5-H),
4.02 (2H, s, SCH2), 5.36 (1H, s, 3-H), 7.26–7.48 (5H, m, Ar–H);
13C NMR (75 MHz, CDCl3): δC 19.6 (CH3), 22.7 (CH3), 36.2,
40.2, 75.7, 76.1, 127.2, 129.1, 130.1, 134.3, 168.8, 171.9; MS
(FAB): m/z 413 (MCsϩ, 100%), 303 (MNaϩ, 25), 281 (MHϩ,
75); HRMS (FAB) calcd. for C14H16O4S (MHϩ): 281.0848.
Found: 281.0830.
(d 1JCF 232 Hz, SCHF), 121.6 (2-C), 126.7, 128.3, 128.6, 129.2,
129.5, 134.3 (2C), 135.6, 135.8, 165.1 (d JCF 29 Hz, C᎐O); 19F
2
᎐
NMR (376 MHz, CDCl3): δF Ϫ158.7 (d 1JHF 52 Hz); MS (FAB):
m/z 302 (Mϩ, 100%); HRMS (FAB) calcd. for C17H15FO2S:
302.0777. Found: 302.0762.
Prenyl (2-fluoro-2-phenylsulfanyl)acetate 19. A solution of
DFIT (87%, 350 mg, 1.2 mmol) and sulfide 13 (257 mg, 1.10
mmol) in DCM (6 mL) was stirred for 2 h. Work-up according
to the general procedure followed by flash chromatography
(SiO2, PE 30–40:ether 90:10) yielded the fluoride 19 (178 mg,
64%) as a colourless oil; Rf 0.40 (SiO2, PE 30–40:ether 90:10);
Ethyl (phenylsulfanyl)acetate 15. Colourless oil; Rf 0.65 (SiO2,
PE 30–40:ether 80:20); IR (thin film/cmϪ1): νmax 2982s (CH),
1736s (C᎐O), 1582m, 1273s, 1135s, 1028s, 743s, 691s; 1H NMR
᎐
(500 MHz, CDCl3): δH 1.20 (3H, t J 9 Hz, CH3), 3.61 (2H, s,
SCH2) 4.14 (2H, q J 9 Hz, OCH2), 7.20–7.40 (5H, m, Ar–H);
13C NMR (75 MHz, CDCl3): δC 14.0 (CH3), 36.8 (SCH2), 61.5
IR (thin film/cmϪ1): νmax 2975m, 2936m (CH), 1752s (C᎐O),
᎐
1275s, 1177s, 1034s, 957s, 748s, 693s; 1H NMR (300 MHz,
CDCl3): δH 1.68 (3H, s, CH3), 1.75 (3H, s, CH3) 4.58 (2H, d J 8
2
(OCH2), 126.9, 129.0, 129.9, 135.0 (Cipso), 169.8 (C᎐O); MS
Hz, 1-H), 5.21–5.25 (1H, m, 2-H), 6.07 (1H, d JHF 52 Hz,
᎐
(FAB): m/z 196 (Mϩ, 65%), 123 (Mϩ, 100); HRMS (FAB) calcd.
SCHF), 7.33–7.57 (5H, m, Ar–H); 13C NMR (75 MHz, CDCl3):
1
for C10H12O2S: 196.0558. Found: 196.0550.
δC 17.9 (CH3), 25.7 (CH3), 63.0 (1-C), 94.2 (d JCF 234 Hz,
SCHF), 117.3 (2-C), 128.9, 129.0, 129.3, 134.0, 140.4, 165.3
2
4-Thiochromanyl (phenylsulfanyl)acetate 16. Yellow oil; Rf
0.55 (SiO2, PE 30–40:ether 85:15); IR (thin film/cmϪ1): νmax
(d JCF 29 Hz, C᎐O); 19F NMR (470 MHz, CDCl3): δF Ϫ158.6
᎐
(d, 2JFH 53 Hz); MS (FAB): m/z 387 (MCsϩ, 100%), 293 (MKϩ,
60), 277 (MNaϩ, 80), 255 (MHϩ, 85); HRMS (FAB) calcd. for
C13H15FO2S: 255.0855. Found: 255.0861.
3058w, 2925w (CH), 1725s (C᎐O), 1586m, 1477m, 1438m,
᎐
1
1264s, 1126s, 1002m, 962m, 746s, 691s; H NMR (300 MHz,
CDCl3): δH 2.03–2.13 (1H, m, 3-H), 2.29–2.35 (1H, m, 3-H),
2.75–2.82 (1H, m, 2-H), 3.09–3.19 (1H, m, 2-H), 3.67 (2H, s,
(3R,2ЈR/2ЈS )-4,5-Dihydro-3-(2Ј-fluoro-2Ј-phenylsulfanyl)-
acetoxy-4,4-dimethyl-2(3H)-furanone 20. A solution of DFIT
(83%, 219 mg, 0.71 mmol) and sulfide 14 (186 mg, 0.62 mmol)
in DCM (5 mL) was stirred overnight. Work-up according to
the general procedure followed by flash chromatography (SiO2,
PE 30–40:ether 60:40) afforded the fluoride 20 (103 mg, 53%) as
a colourless oil (3R,2ЈR:3R,2ЈS 1:1); Rf 0.37 (SiO2, PE 30–40:
ether 60:40); IR (thin film/cmϪ1): νmax 2969s (CH), 1770s
SCH2), 6.05 (1H, t J 3 Hz, 4-H), 7.01–7.54 (9H, m, Ar–H); 13
C
NMR (75 MHz, CDCl3): δC 22.4, 28.7, 37.8, 70.1 (4-C), 125.1,
127.6, 128.0, 130.0, 130.8, 131.1, 132.7, 135.0, 135.5, 169.9
(C᎐O); MS (FAB): m/z 316 (Mϩ, 75%), 219 (35); HRMS (FAB)
᎐
calcd. for C17H16O2S2 (MHϩ): 316.0598. Found: 316.0592.
General procedure for the fluorination of substrates using
DFIT. A solution of DFIT in DCM was prepared in a 25 mL
polypropylene flask protected from light by aluminium foil. The
solution was cooled to 0 ЊC in an ice–salt bath and a solution of
the substrate in DCM was then added via cannula. The mixture
was left to stir at this temperature. Upon completion (TLC) the
reaction was quenched with water and extracted with DCM.
The combined extracts were dried (MgSO4) and concentrated
in vacuo. Flash chromatography yielded pure materials.
(C᎐O), 1476m, 1378m, 1260s, 1157s, 1077s, 1013s, 754s, 692s;
᎐
1H NMR (300 MHz, CDCl3): δH 1.02, 1.06, 1.07, 1.10 (12H, 4 ×
s, 4 × CH3), 3.97–4.04 (4H, m, 5-H), 5.25 (1H, s, 3-H), 5.32 (1H,
s, 3-H), 6.18 (1H, d 2JHF 51 Hz, 2Ј-H), 6.23 (1H, d 2JHF 51 Hz,
2Ј-H), 7.49–7.67 (5H, m, Ar–H); 13C NMR (100 MHz, CDCl3):
δC 19.7 (CH3), 19.8 (CH3), 22.6 (CH3), 22.8 (CH3), 40.3 (4-C),
40.4 (4-C), 76.1 (3-H), 76.1 (3-H), 76.4 (4-H), 76.5 (4-H), 93.4 (d
1
1JCF 230 Hz, 2Ј-H), 94.1 (d JCF 233 Hz, 2Ј-H), 129.4, 129.4,
2
129.9, 130.2, 133.2, 133.2, 135.0, 135.0, 164.4 (d JCF 13 Hz,
Phenyl (2-fluoro-2-phenylsulfanyl)acetate 17. A solution of
DFIT (185 mg, 0.73 mmol) and sulfide 11 (163 mg, 0.67 mmol)
in DCM (5 mL) was stirred overnight. Work-up according to
the general procedure followed by flash chromatography (SiO2,
PE 30–40:ether 95:5) gave the fluoride 17 (126 mg, 72%) as a
white solid; Rf 0.52 (SiO2, PE 30–40:ether 85:15); IR (thin
1Ј-C), 164.7 (d 2JCF 13 Hz, 1Ј-C); 19F NMR (376 MHz, CDCl3):
2
2
δF Ϫ160.2 (d JFH 51 Hz), Ϫ156.3 (d JFH 51 Hz); MS (FAB):
m/z 298 (Mϩ 55%), 279 ([M Ϫ F]ϩ, 100); HRMS (FAB) calcd.
for C14H15O4FS: 298.0675. Found 298.0670.
Ethyl (2,2-difluoro-2-phenylsulfanyl)acetate 21. A solution of
DFIT (75%, 671 mg, 2 mmol) and sulfide 15 (200 mg, 1.00
mmol) in DCM (7 mL) was stirred overnight. The crude
film/cmϪ1): νmax 3049w, 2951w, 1742s (C᎐O), 1588m, 1483m,
᎐
1434m, 1309w, 1246s, 1190s, 1015s, 931m, 840w, 742w, 686m;
J. Chem. Soc., Perkin Trans. 1, 2002, 2809–2815
2813

View Article Online
material was absorbed onto silica gel and washed with PE
30–40. A second wash with PE 30–40:ether 80:20 afforded the
difluoride 21 (188 mg, 80%) as a colourless oil; Rf 0.48 (SiO2,
PE 30–40:ether 90:10); IR (thin film/cmϪ1): νmax 3063m, 2986s,
3-Fluoro-5-phenyl-2(5H)-furanone 31. A solution of fluoro-
sulfoxide 30 (94 mg, 0.31 mmol) in toluene (5 mL) was refluxed
for 20 min. Concentration in vacuo followed by flash chroma-
tography (SiO2, PE 30–40:ether 95:5) afforded the fluoride 31
(43 mg, 72%) as a colourless oil; Rf 0.16 (SiO2, PE 30–40:ether
2940m (CH), 1767 (C᎐O), 1476s, 1442s, 1371s, 1234s, 1106s,
᎐
1
1017s, 978s, 753s, 691s; H NMR (300 MHz, CDCl3): δH 1.24
85:15); IR (thin film/cmϪ1): νmax 3108w (CH), 1783s (C᎐O),
᎐
1
(3H, t J 4 Hz, CH3), 4.23 (2H, q J 4 Hz, CH2), 7.36–7.61 (5H,
1678m, 1288w, 1108m; H NMR (300 MHz, CDCl3): δH 5.88
m, Ar–H); 13C NMR (100 MHz, CDCl3): δC 13.76 (CH3), 63.5
(1H, dd 3JHF 6 Hz, 3JHH 2 Hz, 4-H), 6.76 (1H, t 3JHH 2 Hz, 4JHF
2
1
(CH2), 120.0 (t JCF 287 Hz), 124.9 (Cipso), 129.3, 130.6, 136.7,
Hz, 5-H), 7.18–7.38 (5H, m, Ar–H); 13C NMR (100 MHz,
3 2
2
161.6 (t JCF 32 Hz, C᎐O); 19F NMR (282 MHz, CDCl3): δF
CDCl3): δC 79.0 (d JCF 8 Hz, 5-C), 126.1 (d JCF 6 Hz, 4-C),
᎐
Ϫ82.7; MS (FAB): m/z 232 (Mϩ 100%), 213 ([M Ϫ F]ϩ, 20), 159
(90); HRMS (FAB) calcd. for C10H10F2O2S: 232.0370. Found:
232.0362.
127.2, 129.6, 130.3, 134.0 (d 4JCF 2 Hz, Cipso), 148.6 (d 1JCF 281
Hz, 3-C), 165.0 (d JCF 32 Hz, C᎐O); 19F NMR (282 MHz,
2
᎐
CDCl3): δF Ϫ142.1 (d JFH 6 Hz); MS (FAB): m/z 179 (MHϩ,
3
65%), 159 ([M Ϫ F]ϩ, 100); HRMS (FAB) calcd. for C10H8FO2
(MHϩ): 179.0508. Found: 179.0502.
Ethyl (2,2-difluoro-2-phenylsulfinyl)acetate 22. A solution of
DFIT (75%, 754 mg, 2.28 mmol) and sulfide 15 (150 mg, 0.76
mmol) in DCM (10 mL) was stirred overnight. Work-up
according to the general procedure followed by flash chroma-
tography (SiO2, PE 30–40:ether 95:5) afforded the difluoro-
sulfoxide 22 (71 mg, 38%) as a colourless oil; Rf 0.11 (PE
30–40:ether 90:10); IR (thin film/cmϪ1): νmax 3064m, 2988s,
3-Fluoro-2(5H)-furanone 3329b. A solution of DFIT (91%,
1.25 g, 4.2 mmol) and sulfide 3230 (400 mg, 2.1 mmol) in DCM
(15 mL) was stirred overnight. The reaction was worked-up as
usual and the crude product taken into toluene (10 mL) and
stirred at reflux for 30 min. After cooling to room temperature
the solution was concentrated in vacuo then chromatographed
(SiO2, PE 30–40:ether 70:30) to afford the fluoride 33 (92 mg,
43%) as a yellow oil; Rf 0.27 (SiO2, DCM); IR (thin film/cmϪ1):
2942m (CH), 1760s (C᎐O), 1475s, 1447s, 1373s, 1306s, 1132s,
᎐
1062s, 1031s, 964s, 854m, 833m, 752m, 689s; 1H NMR
(300 MHz, CDCl3): δH 1.18 (3H, t J 7 Hz, CH3), 4.19 (2H, q J 7
Hz, CH2), 7.49–7.67 (5H, m, Ar–H); 13C NMR (75 MHz,
νmax 2929m (CH), 1777s (C᎐O), 1680s, 1450s, 1332m, 1107s,
᎐
1
1
CDCl3): δC 14.2 (CH3), 64.6 (CH2), 118.4 (t JCF 302 Hz, 2-C),
1040s, 824m, 760s; H NMR (300 MHz, CDCl3): δH 4.81 (2H,
126.4, 129.8, 133.6, 136.44 (Cipso), 159.7 (t 2JCF 28 Hz, C᎐O); 19
F
2
3
3
3
dd JHH 6 Hz, JHH 2 Hz, 5-H), 6.79 (1H, dd JHF 4 Hz, JHH
2
᎐
2
Hz, 4-H); 13C NMR (75 MHz, CDCl3): δC 66.6 (d JCF 8 Hz,
3
NMR (282 MHz, CDCl3): δF Ϫ110.3 (ABq JFH 578, 228 Hz);
MS (FAB): m/z 271 (MNaϩ 10%), 249 (MHϩ, 100); HRMS
(FAB) calcd. for C10H11F2O3S (MHϩ): 249.0397. Found:
249.0388; plus 21 (34 mg, 19%).
5-C), 123.3 (d 2JCF 8 Hz, 4-C), 148.5 (d 1JCF 275 Hz, 3-C), 165.5
2
(d JCF 32 Hz, C᎐O); 19F NMR (282 MHz, CDCl3): δF Ϫ146.8
᎐
(t J 6 Hz).
3-Fluoro-4,5-dihydro-3-phenylsulfanyl-anti-5-phenyl-2(3H)-
furanone 27. A solution of DFIT (75%, 365 mg, 1.1 mmol) and
lactone 2627 (300 mg, 1.1 mmol) in DCM (5 mL) was stirred for
7 h. Work-up according to the general procedure followed by
flash chromatography (SiO2, PE 30–40:ether 90:10) afforded the
fluoride 27 (197 mg, 62%) as colourless crystals; mp 98–100 ЊC
(PE 30–40:ether); Rf 0.29 (SiO2, PE 30–40:ether 80:20); IR (thin
Crystal data for 27. C16H13FO2S, M = 288.32, monoclinic,
a = 6.2010(10), b = 7.933(2), c = 14.948(3) Å, β = 92.11(3)Њ,
U = 734.8(3) Å3, T = 293(2) K, space group Pc, Z = 2, µ(Mo-Kα)
= 0.229 mmϪ1, 1367 reflections measured, 1367 unique (Rint
=
0.0000) which were used in all calculations. The final wR(F 2)
was 0.1842 (all data). Absolute configuration not determined
by X-ray determination, Flack parameter 0.26(25). CCDC
193940. See http://www.rsc.org/suppdata/p1/b2/b209079a/ for
crystallographic files in CIF or other electronic format.
film/cmϪ1): νmax 3062w, 1789s (C᎐O), 1598w, 1474w, 1442w,
᎐
1328w, 1279w, 1203m, 1180m, 1041m, 1014m, 938w, 847w,
749m, 697s; 1H NMR (400 MHz, CDCl3): δH 2.66–2.74 (1H, m,
4-H), 2.89 (1H, dd J 11, 4 Hz, 4-H), 5.51 (1H, dd J 8, 4 Hz,
5-H), 7.33–7.65 (10H, m, Ar–H); 13C NMR (75 MHz, CDCl3):
δC 43.7 (d 2JCF 21 Hz, 4-C), 77.1 (d 3JCF 4 Hz, 5-C), 99.8 (d 1JCF
246 Hz, 3-C), 125.8, 127.3, 128.9, 129.1, 129.3, 130.4, 135.7,
Acknowledgements
We are grateful to the EPSRC for the award of a studentship to
M.F.G.
136.6, 167.3 (d 2JCF 31 Hz, C᎐O); 19F NMR (471 MHz, CDCl3):
᎐
3
δF Ϫ132.4 (d JFH 16 Hz); MS (FAB): m/z 288 (Mϩ, 23%), 269
([M Ϫ F]ϩ, 100), 223 (100); Anal: calcd. for C16H13FO2S: C,
References
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᎐
940w, 750m, 697m; 1H NMR (400 MHz, CDCl3): δH 2.23–2.40
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2814
J. Chem. Soc., Perkin Trans. 1, 2002, 2809–2815

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J. Chem. Soc., Perkin Trans. 1, 2002, 2809–2815
2815