New copper(I) and iron(II) complexes for atom transfer radical macrocyclisation reactions

Article abstract of DOI:10.1039/a908245j

New Cu(I) and Fe(II) complexes have been synthesized and proved to be efficient catalysts for atom transfer radical addition (ATRA) reactions. The catalytic activity was found to be greater than existing atom transfer systems based upon CuCl(bipyridine) or RuCl₂(PPh₃)₃, for example. The addition of a reducing agent considerably improved the efficiency of the usual procedures. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/a908245j

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New copper(I) and iron(II) complexes for atom transfer radical
macrocyclisation reactions
Floryan De Campo, Dominique Lastécouères and Jean-Baptiste Verlhac*
1
Laboratoire de Chimie Organique et Organométallique (UMR 5802 CNRS),
Université Bordeaux I, 351 cours de la Libération, 33405 Talence Cedex, France.
E-mail: j-b.verlhac@lcoo.u-bordeaux.fr
Received (in Cambridge, UK) 14th October 1999, Accepted 23rd December 1999
New Cu() and Fe() complexes have been synthesized and proved to be efficient catalysts for atom transfer radical
addition (ATRA) reactions. The catalytic activity was found to be greater than existing atom transfer systems based
upon CuCl(bipyridine) or RuCl2(PPh3)3, for example. The addition of a reducing agent considerably improved the
efficiency of the usual procedures.
catalyst are its low solubility in the reaction solvent and the
Introduction
poor conversion in the attempts to prepare higher lactones; in
The synthesis of macrolactones has received considerable atten-
the latter case, oligomerisation of the starting material is gener-
tion during the past ten years due to their presence in natural
ally observed. Recently, more active copper catalysts have been
substances1 and to their biological activity against tumorous
described for the preparation of cyclic lactams and their appli-
disease2 for example.
Synthetic methods allowing the preparation of 8- to 10-
membered or higher lactones are scarce and generally involve
cation in atom transfer polymerisation has been reported.10
Results and discussion
high dilution techniques or the aid of a template structure.
With the exception of esterification reactions, few methods have
been reported for the synthesis of lactones from an acyclic pre-
cursor. Radical methods are powerful tools for carbon–carbon
bond formation by intramolecular addition of a carbon radical
to an unsaturated system; organotin hydride mediated cyclis-
ation of ω-iodoalkyl unsaturated esters has been successfully
reported by Porter et al.3 Radical methods have also been used
for the preparation of macrocyclic ethers using syringe-pump
techniques in order to avoid oligomerisation or direct reduction
of the substrate.4 Atom transfer radical addition (ATRA) reac-
tions, which make use of the redox properties of transition
metal complexes in order to initiate the reaction by homolytic
cleavage of a carbon–halogen bond, could be used as an alter-
native to organotin hydride for the generation of a carbon
centered radical. Moreover, the termination step introduces a
versatile halogen atom into the product which is then useful
for further functionalisation. It can also be expected that the
metal could play a crucial role in the control of the cyclisation
process as the radical is generated in the vicinity of the metal
complex. Thus, a new class of catalysts, which are most often
transition metal complexes such as RuCl2(PPh3)3,5 FeCl2-
(P(OEt)3)3,6 Co(dimethylglyoxime)2,7 CuCl(bpy)5 (bpy = 2,2Ј-
bipyridine) or a mixture of iron metal and copper bromide,8
has been described in ATRA reactions. Speckamp et al. have
reported the synthesis of 5- to 8-membered lactones by cyclis-
ation of unsaturated trichloroacetates using Cu()Cl(bpy) as a
catalyst.9 The major problems associated with the use of this
We recently reported the preparation of copper() or iron()
complexes that could circumvent the problems associated with
poor solubility and conversion.11 Due to their better solubility
and higher catalytic activity, only small amounts of the com-
plex (3 to 10 mol%) are required for completion of the reaction.
We describe herein the results obtained in the cyclisation of
unsaturated trichloroacetates bearing carbon chains of up to
seven carbon atoms. Introduction of a poly(ethyleneglycol)
chain into the unsaturated moiety of these esters allowed us to
obtain 9- to 18-membered macrocyclic lactones.
Ligands L1, L2 and L3 were synthesised according to liter-
ature procedures.12 The catalyst is prepared in situ by reacting
copper() or iron() chloride with one equivalent of the ligand.
Suitable radical precursors 2a–i were readily prepared from the
appropriate alkenyl alcohol or ethylene glycol precursors. In a
typical procedure, treatment of allyl alcohol 1a with trichloro-
acetyl chloride in dichloromethane at 0 ЊC in the presence of
triethylamine furnished the trichloroester 2a in 65% yield
(Scheme 1).
The cyclisation reactions were performed in 1,2-dichloro-
ethane at 80 ЊC for 12–48 h under an argon atmosphere. Work
up was performed by chromatography of the reaction mixture
on silica using petroleum ether–ethyl acetate as eluent. The
nature and the amount of the catalyst, as well as the reaction
yields, are indicated in Table 1. The yields of cyclisation of both
pent-4-enyl trichloroacetate 2c and hex-5-enyl trichloroacetate
2d were subsequently improved by the use of these new catalyst
DOI: 10.1039/a908245j
J. Chem. Soc., Perkin Trans. 1, 2000, 575–580
This journal is © The Royal Society of Chemistry 2000
575

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Table 1 Cyclisations of unsaturated trichloroesters in 1,2-dichloroethane at 80 ЊC (one equivalent of ligand with respect to the metal)
Precursor
Product
Catalyst (ratio)
Yield (%)
CuClؒL3 (10 mol%)
FeCl2ؒL2 (10 mol%)
48
55
CuClؒL1 (10 mol%)
FeCl2ؒL2 (0.3 mol%)
CuClؒL3 (3 mol%)
CuClؒbpy (10 mol%)
99
46
90
47
CuClؒL1 (10 mol%)
FeCl2ؒL2 (3 mol%)
CuClؒL3 (10 mol%)
CuClؒbpy (10 mol%)
53
50
53
4
CuClؒL1 (10 mol%)
CuClؒL3 (10 mol%)
FeCl2ؒL2 (10 mol%)
CuClؒbpy (30 mol%)
51
70
34
5
Scheme 1 Synthetic scheme for the preparation of unsaturated trichloroesters.
systems. The best result was obtained with ligand L1 which
allowed quantitative conversion in the case of 2c. The use of
complexes FeCl2ؒL2 or CuClؒL3, depending on the substrate,
allowed us to decrease considerably the complex–substrate ratio
without significant alteration of the yield. Ligand L2 associated
with copper() gave very poor results, but surprisingly when
used with iron() chloride a very efficient catalyst was obtained
and trichloroester 2c was converted to lactone 3c in 46% yield
even in the presence of 0.3 mol% of catalyst. Moderate yields
of large ring lactones were obtained in the presence of these
new catalysts even though it was nearly impossible to obtain
cyclised products 3d or 3e with the copper()–bipyridine
complex.
The structure of compound 3e was proven by complete
reduction of the racemic mixture to the unsubstituted deriv-
ative 413 with Bu3SnH–AIBN (Scheme 2). When the unsatur-
ated side chain possesses more than three carbon atoms the
cyclisation process proceeds in an endo manner (Scheme 3).
Indeed, the most stable conformation for the ester func-
tion (s-trans) does not impede the cyclisation step if the carbon
chain is long enough (compounds 2c–i).
Scheme 2 Reduction of trichlorolactone 3e by 3 equivalents of
Bu3SnH.
cyclisation product and an exo pathway is observed, as previ-
ously reported by Barth and Yang (Scheme 3).14 However,
whatever the catalyst, while conversions are very high, isolated
yields remain modest due to partial oligomerisation of the
substrates. With the but-3-enyl precursor 2b no cyclisation
products were observed. In this case, only the s-cis conform-
ation could lead to the cyclised products as the chain is not long
enough to allow any significant overlap of the radical and
alkene orbitals in the s-trans conformation and the endo or exo
cyclisation rate constants are probably lower than those for
intermolecular addition, thus only oligomerisation could be
observed.
With an unsaturated shorter chain (e.g. compound 2a) only
the less favourable conformation (s-cis) can give rise to the
In order to lower the catalyst versus substrate ratio, a
576
J. Chem. Soc., Perkin Trans. 1, 2000, 575–580

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either accelerates the halogen transfer from copper() to the
cyclic radical or allows the reduction of the copper(), formed
by the dimerisation reaction, back to the active catalyst.
For substrate 2d, the introduction of the reducing agent did
not exert any significant effect as the yield and the conversion
were not modified to a large extent. When we applied this
methodology to substrate 2e the ratio of catalyst could be
decreased twofold without any modification of the yield and
conversion.
In all the experiments described, no significant amounts of
telomers were detected as observed with the CuClؒbpy complex.
Due to the better solubility and higher activity of our new
complexes, we were able to perform the cyclisation reaction
with less than 10 mol% of catalyst.
Fig. 1 Cyclisation reaction of substrate 2c in the presencea of: (᭜)
CuClؒL2 ratio 1:1; (᭿) CuClؒL2ؒFe(0) ratio 1:1:10; (᭹) Fe(0)ؒL2.
(a The ratios are given in mol% relative to the substrate.)
We also tested the ability of these complexes to catalyse the
cyclisation of larger unsaturated trichloroesters bearing poly-
ether chains. The metal is expected to act as a template and thus
enhance the cyclisation process. We report here that 9- to 18-
membered polyether rings are readily accessible from ω-polyoxy-
alkenols using copper() or iron() complexes. As far as we
know, the use of these types of catalysts for macrocyclis-
ation reactions and especially for polyether synthesis has been
neglected. Pirrung et al. previously described the synthesis of
9- and 10-membered lactones [in the presence of CuClؒbpy
(30 mol%)] using a rigid backbone in the alkenyl chain and
reported that this catalyst failed to mediate cyclisation of higher
lactones.5
In the presence of the CuClؒL3 complex, the cyclisation of
the trichloroacetates 2f and 2g proceeds smoothly with poor
yields. Using the FeCl2ؒL2 complex, the conversion reached
95% and the yield was notably improved, probably due to the
higher solubility of the resulting complex and a possible tem-
plate effect due to the higher acidity of iron() (Table 2). In
these examples competing telomerisation also occurred, princi-
pally with shorter chains, the cyclisation and telomerisation rate
constants being similar. Comparatively, when the chain is long
enough, as in the case of 2h and 2i, the cyclisation process is
more favourable and yields of lactone are reasonable even with
the CuClؒL3 complex. The selectivity of the cyclisation is note-
worthy as the reaction proceeded cleanly and no side-products
were detected. As previously described for the trichloroacetates
2a–e, the introduction of iron(0) (10 mol%) notably improved
the kinetics of the reactions but had no effect on the yield,
however decomposition of the cyclized product occurred
during the reaction and disappearance of the lactone could be
monitored by GC analysis. These side-reactions also occurred
in the absence of the reducing agent and explain the low yields
obtained with the former substrates.
In conclusion, we have reported that the use of new com-
plexes of iron() or copper() successfully mediated atom trans-
fer radical cyclisation reactions of various trichloroacetates in
the presence of very low quantities of catalyst. While previous
systems did not allow the synthesis of large rings, the CuClؒ
TPA(L3) complex [TPA = tris(pyridin-2-ylmethyl)amine] dis-
played a very high catalytic activity and excellent selectivity.
Cyclisation of medium rings is also possible and in the case of
eight- and nine-membered lactones, the use of the CuClؒL2
complex associated with iron(0) proved to be a significant
improvement. The synthesis of five-membered rings was also
described and the selectivity of this process was found to be
greater than that reported with CuClؒbpy.
Scheme 3 Interpretation of radical cyclisation step a) for short chain
(n = 1 or 2) b) for long chain (n = 3, 4 or 5).
reducing agent iron(0) was added to the reaction mixture. The
best results were obtained with a 1:10 ratio of CuCl:Fe(0)
(in mol%) giving a twofold increase in yield within the same
reaction time. Surprisingly, we observed a perfect correlation
between the conversion (95%) and the yield (95%) due to minor
oligomerisation processes and an enhancement of the catalytic
activity (Fig. 1).
If CuCl is omitted from the reaction vessel the cyclisation
still proceeds in the presence of a mixture of only the ligand
and iron powder. However, a latency phase could be observed
before the beginning of the conversion and the reaction rate is
lowered. This latency phase could be due to the slow dissolution
of traces of iron oxides and hydroxides in the presence of the
ligand as iron powder alone failed to mediate the cyclisation of
trichloroesters. The incapacity of iron metal for such catalysis
has been previously observed in apolar solvents.15 As displayed
in Fig. 1, an additional effect is observed when iron powder is
added to a copper complex. We suggest that the use of iron(0)
Experimental
General requirements
All reactions were carried out under an inert atmosphere of dry
nitrogen and argon for intramolecular cyclisation. Proton and
carbon nuclear resonance (1H and 13C NMR) spectra were
recorded in CDCl3, unless indicated otherwise, using either a
J. Chem. Soc., Perkin Trans. 1, 2000, 575–580
577

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Table 2 Cyclisations of polyoxaalkenyl trichloroesters in 1,2-dichloroethane at 80 ЊC (one equivalent of ligand with respect to the metal)
Precursor
Product
Catalysta
Yield (%)
FeCl2ؒL2
CuClؒL3
CuClؒbpy
56
29
11
FeCl2ؒL2
CuClؒL3
CuClؒbpy
60
29
10
FeCl2ؒL2
CuClؒL3
CuClؒbpy
60
70
10
FeCl2ؒL2
CuClؒL3
CuClؒbpy
60
70
10
a Catalyst to substrate ratio was 10 mol% in all the experiments.
Bruker AC200 (200 MHz, 50 MHz) or an AC250 (250 MHz,
63 MHz) spectrometer. Chemical shifts (δ) are given in ppm
downfield from tetramethylsilane. CH2Cl2 and (CH2Cl)2 were
distilled from CaCl2 powder and stored under an atmosphere of
dry nitrogen. Dry THF and Et2O were distilled from sodium
benzophenone prior to use. Petroleum ether and ethyl acetate
were also distilled for chromatographic purposes. Other com-
mercially available starting materials were used without further
purification. Elemental analysis were performed by the Service
Central d’Analyse (CNRS-Vernaison).
CH O), 5.3–5.5 (m, 2H, CH ᎐), 5.8–6.05 (m, 1H, CH᎐); δ (62.9
᎐ ᎐
2 2 C
MHz; CDCl , Me Si) 69.5 (CH O), 100.0 (CCl ), 120.4 (CH ᎐),
᎐
2
3
4
2
3
129.9 (CH᎐), 163.0 (C᎐O); m/z (CI): 202 (1%, M), 167 (1,
᎐
᎐
M Ϫ Cl), 132 (7, M Ϫ 2Cl), 97 (100, M Ϫ 3Cl), 57 (87,
M Ϫ COCCl3).
Trichloroacetic acid but-3-enyl ester 2b. Yield (55%). IR
νmax(film)/cmϪ1 3080, 2960, 1760 (Found: C, 32.05; H, 3.22; O,
15.07; Cl, 48.64. C6H7Cl3O2 requires C, 33.14; H, 3.24; O, 14.71;
Cl, 48.91%); δH(250 MHz; CDCl3, Me4Si) 2.5 (m, 2H, CH2-
CH᎐), 4.4 (m, 2H, CH O), 5.1–5.3 (m, 2H, CH ᎐C), 5.7–5.9
᎐
᎐
2
2
Typical procedure for trichloroacetylation of alkenols
(m, 1H, CH ᎐CH); δ (62.9 MHz; CDCl , Me Si) 32.1 (CH ),
᎐
2
C
3
4
2
67.7 (CH O), 90.0 (CCl ), 117.9 (CH ᎐), 132.1 (CH᎐), 161.5
(C᎐O).
᎐
᎐
2
᎐
2
3
Trichloroacetyl chloride (0.165 mol) was dissolved in dichloro-
methane (450 ml) and cooled down to 0 ЊC. Alkenol (0.15 mol)
was slowly added, then triethylamine (0.3 mol) in dichloro-
methane solution (100 ml) was added dropwise to the reac-
tion mixture. After 2 hours at 0 ЊC, a 2 M solution of hydro-
chloric acid (120 ml) was poured into the reaction flask. The
organic phase was washed with a saturated solution of sodium
hydrogen carbonate and water until the pH reached 7. After
drying over magnesium sulfate, the solvent was removed
under vacuum. The resulting crude product was purified on a
silica gel column (eluent: petroleum ether–ethyl acetate, 90:10
for compounds 2a–e and 50:50 for compounds 2f–i). Com-
pounds 2c and 2d were synthesized according to literature
procedures.5
Trichloroacetic acid hept-6-enyl ester 2e. Yield (82%). IR
νmax(film)/cmϪ1 3010, 2970, 1760 (Found: C, 40.89; H, 4.38.
C9H13Cl3O2 requires C, 41.62; H, 4.51%); δH(250 MHz; CDCl3,
Me Si) 1.35–1.5 (m, 4H, CH CH ), 1.8 (m, 2H, CH CH᎐), 2.1
᎐
4
2
2
2
(m, 2H, CH CH O), 4.36 (m, 2H, CH O), 4.95 (m, 2H, CH ᎐),
᎐
2
2
2
2
5.79 (m, 1H, CH᎐); δ (62.9 MHz; CDCl , Me Si) 24.8
᎐
C
3
4
(CH CH CH᎐), 27.8 (CH CH O), 28.0 (CH ), 33.2 (CH CH᎐),
᎐
᎐
2
2
2
2
2
2
69.2 (CH O), 89.9 (CCl ), 114.5 (CH ᎐), 138.2 (CH᎐), 161.8
᎐
2
᎐
2
3
(C᎐O).
᎐
Trichloroacetic acid 3-oxahex-5-enyl ester 2f. Yield (82%)
(Found: C, 34.45; H, 3.56. C7H9Cl3O3 requires C, 33.94; H,
3.64%); δH(250 MHz; CDCl3, Me4Si) 3.3 (m, 2H, CH2-
OCOCCl3), 3.55 (m, 2H, CH2CH2OCOCCl3), 4.0 (m, 2H,
Trichloroacetic acid prop-2-enyl ester 2a. Yield (65%). IR
νmax(film)/cmϪ1 3070, 2940, 1760 (Found: C, 29.21; H, 2.53; O,
16.04; Cl, 51.51. C5H5Cl3O2 requires C, 29.52; H, 2.48; O,
15.73; Cl, 52.28%); δH(250 MHz; CDCl3, Me4Si) 4.8 (m, 2H,
᎐CHCH O), 4.7 (m, 2H, CH ᎐), 5.35 (m, 1H, CH᎐); δ (62.9
᎐
᎐
᎐
2
2
C
MHz; CDCl3, Me4Si) 65.4 (CH2OCOCCl3), 66.8 (CH2CH2-
578
J. Chem. Soc., Perkin Trans. 1, 2000, 575–580

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OCOCCl ), 71.86 (᎐CHCH O), 89.53 (CCl ), 117.11 (CH ᎐),
Me4Si) 2.90–3.15 (m, 2H, CH2CCl2), 3.41–3.67 (m, 6H, other
᎐
᎐
2
3
2
3
134.00 (CH᎐), 161.69 (C᎐O).
CH2O), 3.7 (m, 2H, CO2CH2CH2), 4.05 (m, 1H, CHCl), 4.42
(m, 2H, CO2CH2); δC(62.9 MHz; CDCl3, Me4Si) 51.3
(CH2CCl2), 53.4 (CHCl), 66.5 (CO2CH2), 68.5 (CO2CH2CH2),
᎐
᎐
Trichloroacetic acid 3,6-dioxanon-8-enyl ester 2g. Yield (99%)
(Found: C, 37.78; H, 4.36. C9H13Cl3O4 requires C, 37.05; H,
4.46%); δH(250 MHz; CDCl3, Me4Si) 3.52 (m, 2H, CH2O), 3.61
70.7 (CH O), 70.8, 74.1, 82.5 (CCl ), 165.3 (C᎐O).
᎐
2
2
(m, 2H, CH O), 3.7 (m, 2H, CH O), 3.97 (m, 2H, CH CH᎐), 4.2
12,12,14-Trichloro-1,4,7,10-tetraoxacyclopentadecan-11-one
3h. (Found: C, 39.75; H, 4.62; O, 23.93; Cl, 31.98. C11H17Cl3O5
requires C, 39.60; H, 4.53; O, 23.98; Cl, 31.88%); δH(250 MHz;
CDCl3, Me4Si) 2.84–3.11 (m, 2H, CH2CCl2), 3.33–3.81 (m,
12H, CH2O), 4.01 (m, 1H, CHCl), 4.38 (m, 2H, CO2CH2);
δC(62.9 MHz; CDCl3, Me4Si), 48.9 (CH2CCl2), 55.1 (CHCl),
66.3 (CO2CH2), 67.7 (CO2CH2CH2), 69.6 (CH2O), 69.9, 70.2,
᎐
2
2
2
(m, 2H, CH O), 5.15 (m, 2H, CH ᎐), 5.8 (m, 1H, CH᎐); δ (62.9
᎐
᎐
2
2
C
MHz; CDCl3, Me4Si) 68.06 (CH2OCOCCl3), 68.09, 69.17,
70.61, 71.95 (other CH ), 89 (CCl ), 116.83 (CH ᎐), 134.36
᎐
2
2
3
(CH᎐), 161.67 (C᎐O).
᎐
᎐
Trichloroacetic acid 3,6,9-trioxadodec-11-enyl ester 2h.
Yield (69%) (Found: C, 38.92; H, 4.89. C11H17Cl3O5 requires C,
39.34; H, 5.07%); δH(250 MHz; CDCl3, Me4Si) 3.41 (m, 8H,
70.5, 74.1, 82.2 (CCl ), 164.9 (C᎐O).
᎐
2
CH O), 3.55 (m, 2H, CH ), 3.81 (m, 2H, CH CH᎐), 4.25 (m,
15,15,17-Trichloro-1,4,7,10,13-pentaoxacyclooctadecan-14-
one 3i. (Found: C, 41.14; H, 5.61; O, 24.32; Cl, 29.58. C13H21-
Cl3O6 requires C, 41.13; H, 5.58; O, 25.28; Cl, 28.01%); δH(250
MHz; CDCl3, Me4Si) 2.76–3.08 (m, 2H, CH2CCl2), 3.49–3.65
(m, 14H, other CH2O), 3.78 (m, 2H, CO2CH2CH2), 4.11 (m,
1H, CHCl), 4.40 (m, 2H, CO2CH2); δC(62.9 MHz; CDCl3,
Me4Si) 48.81 (CH2CCl2), 55.1 (CHCl), 66.6 (CO2CH2), 68.1
(CO2CH2CH2), 69.2 (CH2O), 70.4, 70.5, 70.7, 70.8, 72.0, 74.4,
᎐
2
2
2
2H, CH OCO), 5.05 (m, 2H, CH ᎐), 5.82 (m, 1H, CH᎐); δ (62.9
᎐
᎐
2
2
C
MHz; CDCl3; Me4Si) 70.35, 70.26, 70.15, 70.07, 68.81 (other
CH ), 67.75 (CH OCOCCl ), 71.56 (᎐CHCH O), 89.4 (CCl ),
᎐
2
2
3
2
3
116.39 (CH ᎐), 134.16 (CH᎐), 161.29 (C᎐O).
᎐
᎐
᎐
2
Trichloroacetic acid 3,6,9,12-tetraoxapentadec-14-enyl ester
2i. Yield (79%) (Found: C, 40.89; H, 5.36. C13H21Cl3O6 requires
C, 41.11; H, 5.53%); δH(250 MHz; CDCl3, Me4Si) 3.37 (m, 12H,
83.1 (CCl ), 165.1 (C᎐O).
᎐
2
CH O), 3.54 (m, 2H, CH CH OCO), 3.78 (2H, m, CH CH᎐)
᎐
2
2
2
2
4.26 (m, 2H, CH OCO), 5.35 (m, 1H, CH᎐); δ (62.9 MHz;
CDCl3, Me4Si) 67.88 (CH2OCOCCl3), 67.95, 69.00, 70.19,
70.21, 70.25, 70.39, 70.42, 71.7 (other CH2), 89.35 (CCl3),
᎐
2
C
Procedure for the reduction of compound 3e to 1-oxacyclodecan-2-
one 4
To a solution of tributyltin hydride (403 mg, 1.39 mmol) in
cyclohexane (2.2 ml) was slowly added a cyclohexane (5 ml)
solution of 3e (110 mg, 0.42 mmol) and AIBN (1.38 mg, 0.008
mmol). After 3 hours at 80 ЊC, the reaction mixture was diluted
with cyclohexane (30 ml) and a saturated solution of potassium
chloride (15 ml) was added. The aqueous layer was extracted
three times with 10 ml of cyclohexane. The organic phases were
evaporated to dryness and the resulting brown oil dissolved in
acetonitrile. The resulting solution was washed three times with
petroleum ether and evaporation provided 60 mg (yield, 92%)
of a yellowish oil. δH(250 MHz; CDCl3, Me4Si) 0.9–1.4 (m,
116.44 (CH ᎐), 134.41 (CH᎐), 161.39 (C᎐O); m/z (FAB, 70 eV):
379 (M ϩ 1), 235 (M Ϫ COCCl3).
᎐
᎐
᎐
2
Typical procedure for cyclisation of alkenyl trichloroacetates
All the reactions were carried out under an argon atmosphere in
1,2-dichloroethane (0.2 M). The ligand (10 to 100 µmol), the
reaction mixture containing the substrate (1 mmol) and the
metal salt (10 to 100 µmol) were degassed separately using the
freeze–pump–thaw procedure (three cycles). The ligand was
then added in order to generate the active catalyst.
12H, CH cyclic), 1.8–2.1 (m, 2H, CH C᎐O), 3.6–3.8 (m, 2H,
᎐
2
2
CH O); δ (62.9 MHz; CDCl , Me Si) 24.7 (CH CH C᎐O), 25.4
᎐
2
2
C
3
4
2
3,3-Dichloro-4-chloromethyltetrahydrofuran-2-one 3a. IR
νmax(film)/cmϪ1 2960, 1760; δH(250 MHz; CDCl3, Me4Si) 3.3–
3.4 (m, 1H, CHCl), 3.8 (dd, J 9.5, 11.5 Hz, 1H) and 4.0 (dd,
J 4.6, 11.5 Hz, 1H) (CH2Cl), 4.2 (dd, J 8.8, 9.3 Hz, 1H) and 4.7
(dd, J 7.1, 9.3 Hz, 1H) (CH2O); δC(62.9 MHz; CDCl3, Me4Si)
(CH CH CH O), 25.5 (CH CH CH C᎐O), 28.2 (CH CH O),
᎐
2
2
2
2
2
2
2
2
28.5 (CH CH CH CH O), 28.7 (CH CH CH CH C᎐O), 33.9
᎐
2
2
2
2
2
2
2
2
(CH C᎐O), 63.6 (CH O), 164.2 (C᎐O).
᎐
᎐
2
2
39.2 (CH2Cl), 52.9 (CHCl), 68.2 (CH2O), 78.2 (CCl2), 166.7
Acknowledgements
ϩ
(C᎐O); m/z (CI, NH ): 167 (1, M Ϫ Cl), 132 (32, M Ϫ 2Cl),
᎐
4
97 (100, M Ϫ 3Cl).
We are indebted to Dr B. Maillard for fruitful discussion and
to the Région Aquitaine for financial support.
Compounds 3c, 3d: See reference 5. 3,3,5-Trichlorooxecan-2-
one 3e. IR νmax(film)/cmϪ1 2970, 1770; δH(250 MHz; CDCl3,
Me4Si) 1.5–2.2 (m, 8H), 2.9 (dd, J 3.7, 15.4 Hz, 1H) and 3.2 (dd,
J 8.4, 15.4 Hz, 1H) (CH2CCl2), 3.83 (m, 2H, CH2O), 4.22–4.30
(m, 1H, CHCl); δC(62.9 MHz; CDCl3, Me4Si) 20.3, 23.5, 24.7,
29.2 (CH2), 49.3 (CH2CCl2), 56.4 (CHCl), 69.6 (CH2O), 82.4
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᎐
2
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(CO CH CH ), 77.9 (CH O), 82.1 (CCl ), 165 (C᎐O).
᎐
2
2
2
2
2
9,9,11-Trichloro-1,4,7-trioxacyclododecan-8-one 3g. (Found:
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