A convenient synthesis of z-allylsilanes with good stereoselectivity promoted by samarium diiodide

Article abstract of DOI:10.1055/s-2006-958436

Synthesis of Z-allylsilanes in high or good yields and with good stereoselectivity is achieved from O-acetylated 1-silyl-3-chloro alcohols promoted by SmI₂. The starting compounds were easily prepared from 2-chloroaldehydes and a mechanism is p

Full text of DOI:10.1055/s-2006-958436

LETTER
75
A Convenient Synthesis of Z-Allylsilanes with Good Stereoselectivity
Promoted by Samarium Diiodide
Synthesis
o
of
Z
-Allylsila
s
ne
s
é M. Concellón,* Humberto Rodríguez-Solla, Carmen Simal, Cecilia Gómez
Departamento Química Orgánica e Inorgánica, Universidad de Oviedo, C/ Julián Clavería, 8, 33006, Oviedo, Spain
Fax jmcg@fq.uniovi.es
Received 9 October 2006
treatment of O-acetyl 1-trimethylsilyl-3-chloroalkan-2-
ols with SmI2 and with high Z-stereoselectivity. A mech-
anism to explain the stereoselectivity of this process is
also proposed.
Abstract: Synthesis of Z-allylsilanes in high or good yields and
with good stereoselectivity is achieved from O-acetylated 1-silyl-3-
chloro alcohols promoted by SmI2. The starting compounds were
easily prepared from 2-chloroaldehydes and a mechanism is pro-
posed to explain the stereoselectivity of the b-elimination reaction.
The starting materials 3 were easily prepared by treatment
of a-chloroaldehydes 110 with (trimethylsilyl)methyl-
lithium to obtain the corresponding chlorohydrins 2.
Subsequent acetylation of products 2 afforded the starting
compounds 3, as mixture of diastereoisomers 1:1, with
good yields (65–86% for the overall process;
Scheme 1).11
Key words: Allylsilanes, diastereoselectivity, eliminations, samar-
ium
Allylsilanes are important building blocks and are widely
used in organic synthesis. Consequently, a number of re-
views have been published describing the synthetic appli-
cations of the allylsilanes.1 Parallel with this work and for
the sustained growth of their synthetic applications, many
methods for the synthesis of allylsilanes have been report-
ed. Mainly, the published syntheses afford E-allylsilanes.2
To the best of our knowledge, only two methods can be
used to prepare Z-allylsilanes efficiently with high stereo-
selectivity in which the structure of the former compounds
can be varied. Thus, the Wittig reaction utilizing an un-
usual phosphorane, such as tris(2-methylphenyl)phospho-
rane affords Z-allylsilanes with high stereoselectivity,3
and the preparation of Z-allylsilanes with high stereo-
selectivity can be also achieved by metalation of alk-1-
enes with a mixture of n-BuLi and t-BuOK followed by
subsequent reaction with chlorotrimethylsilane.4 Other re-
ported syntheses of Z-allylsilanes require several steps
and the final yields are low5 or present the drawback of the
utilization of Z-unsaturated compounds as starting materi-
als.6 Finally, other methods give the allylsilane contami-
nated with other by-products.6a For all these reasons, an
alternative synthesis of Z-allylsilanes in which only one
regioisomer is obtained and the double bond is generated
with good stereoselectivity would be desirable.
OH
O
Li
SiMe3
1)
R
SiMe3
R
H
2) H3O+
Cl
Cl
1
2
1) Ac2O
2) H3O+
OAc
65–86% over
3 steps
R
SiMe3
Cl
3
Scheme 1 Synthesis of starting materials 3
The reaction of various O-acetyl 1-trimethylsilyl-3-chlo-
12
roalkan-2-ols 3 in THF with SmI2 at reflux for eight
hours afforded the corresponding allylsilanes 4 in moder-
ate or quantitative yields and generally with good Z-ste-
reoselectivity (Scheme 2 and Table 1). When this process
was carried out at room temperature, no reaction took
place. It is noteworthy that compounds 4 were obtained
with good stereoselectivity from a mixture of diastereo-
isomers (roughly 1:1) of starting materials 3.13
Previously, we have reported the synthesis of vinyl
halides,7 vinylsilanes8 and non-functionalized alkenes9
with high Z-selectivity, promoted by SmI2. The SmI2-
mediated metalation of non-activated C–Cl bonds9 was
carried out in the presence of light produced by five
100 W household lamps.
OAc
SmI2
R
SiMe3
R
SiMe3
THF, ∆
Cl
3
4
As part of our program concerning the development of
new b-elimination reactions mediated by SmI2, we wish to
report herein a new and easy access to Z-allylsilanes, by
Scheme 2 Synthesis of Z-allylsilanes 4
The best results in terms of stereoselectivity were ob-
tained when linear aliphatic aldehydes 1 were utilized
(Table 1, entries 1, 2, and 4–6). This reaction can also be
performed on cyclic substrates. Thus, when the reaction
SYNLETT 2007, No. 1, pp 0075–0078
0
4.
0
1.
2
0
0
7
Advanced online publication: 20.12.2006
DOI: 10.1055/s-2006-958436; Art ID: G29906ST
© Georg Thieme Verlag Stuttgart · New York

76
J. M. Concellón et al.
LETTER
O
was carried out using a-chlorocyclohexanecarboxalde-
hyde (1c) the exocyclic double bond was obtained in high
yield (Table 1, entry 3). The b-elimination reaction can be
carried out on unsaturated compounds 3 (entries 4 and 5)
with the other double bonds being unaffected.
OAc
1)
Li
SiMe3
SiMe3
H
7
7
2) H3O+
3) Ac2O
4) H3O+
Cl
Cl
1i
3i
3 SmI2
THF, reflux, 8 h
The reaction of compounds 3f or 3g (obtained from 3-
phenylpropanal and 3-phenylbutanal) with SmI2 afforded
the corresponding allylsilanes in quantitative or moderate
yields, respectively. However, the allylsilane 4g was iso-
lated with lower stereoselectivity (Z/E ratio = 70:30,
Table 1, entry 7).
E/Z 50:50
>99% yield
SiMe3
7
4i
Scheme 3 Synthesis of product 4i
When the aryl-substituted O-acetyl chlorohydrin 3h was
used the corresponding E-allylsilane was obtained with
good E-stereoselectivity (Table 1, entry 8).
a six-membered-ring intermediate (depicted as I or II in
Scheme 4) is generated through chelation of the highly
oxophilic SmIII center with the carbonyl oxygen atom of
the acetoxy group.16 This coordination favors the elimina-
tion reaction and could justify the mixture of products
obtained when the elimination was carried out from non-
acetylated chlorohydrins 2. Moreover, we suppose that
silicon plays a crucial role. Surprisingly, the metalation of
the apparently non-activated C–Cl bond in products 3
took place in the absence of visible light. This is in con-
trast to the synthesis of Z-alkenes where a photoinduction
was required to produce the metalation of the C–Cl bond
by SmI2.9 This easier metalation could take place due to
the g-effect produced by the silicon atom.17
Table 1 Synthesis of Allylsilanes 4
Entry
4
R
Z/Ea
Yield (%)b
60
1
2
3
4
5
6
7
8
4a
4b
4c
4d
4e
4f
n-C6H13
85:15
85:15
–
n-C10H20
-(CH2)5-
65
95
CH2=CH(CH2)7
(Z)-EtCH=CH(CH2)4
PhCH2
86:14
81:19
85:15
70:30
14:86
>99
>99
>99
50
In the proposed transition-state model I, the trimethyl-
silylmethyl group (Me3SiCH2-) adopts an equatorial posi-
tion to avoid 1,3-diaxial interactions with the samarium
coordination sphere, and R an axial position to avoid
interactions with the samarium coordination sphere and
taking into account that there are no important 1,3-diaxial
interactions due to the presence of both oxygen atoms in
those positions (Scheme 4).
4g
4h
PhCH(Me)
Ph
83
a Z/E ratio was determined by GC-MS, and/or 1H NMR (300 MHz)
analysis of the crude products 4.
b Isolated yield of pure compounds 4 after column chromatography
based on compounds 3.
A 1,2-elimination reaction from I such as that shown in II,
affords Z-alkenes. The isolation of 4 with high levels of Z-
stereoselectivity from the mixture of diastereoisomers 1
can be explained by assuming that the diastereoisomer
with a more suitable conformation for coordination of the
Sm(III) center with the carbonyl oxygen of the acetoxy
group reacts more readily, while the other diastereoisomer
epimerizes before the elimination takes place.7,9 An alter-
native explanation could be given taking into account that
The Z/E ratio was determined on the crude reaction prod-
ucts by GC-MS and H NMR (300 MHz) spectroscopy.
1
The Z- or E-relative configuration of the C–C double bond
generated in allylsilanes 4 was assigned on the basis of the
1
value of the H NMR coupling constants between the
olefinic protons of compounds 4a, 4b, 4d–h, and/or by
comparison with the NMR data previously reported in the
literature for 4a,4 4b,2i 4c,14 4f,6a and 4h.15
The acetyl group in compounds 3 is believed to play a key the chelate intermediate I may also be formed from the
role in the observed reaction outcome. Accordingly, when radical intermediate 5 with preference due to its higher
the reaction was carried out on non-acetylated chloro- stability (less steric interactions).
hydrins (compounds 2), a complex mixture of products
was obtained.
O
OAc
SmI2
D
I2Sm
R
SmI2
D
3a–g
SiMe3
4a–g
R
O
Taking into account the results obtained in the synthesis
of disubstituted allylsilanes 4a–h, we also performed this
process on substrate 3i (derived from an a-chloro-a-alky-
lated aldehyde10b 1i). However, in this case a 1:1 Z/E mix-
ture of the trisubstituted allylsilane was obtained
(Scheme 3).
5
SiMe3
O
H
I2Sm
SmI2
H
O
O
R
O
The observed stereochemistry of alkenes 4a–g might be
explained assuming a chelation-control model. In this
sense, after metalation of the C–Cl bond of compounds 3,
R
SiMe3
SiMe3
I
II
Scheme 4 Mechanistic proposal for the conversion of 3a–g to 4a–g
Synlett 2007, No. 1, 75–78 © Thieme Stuttgart · New York

LETTER
Synthesis of Z-Allylsilanes
77
37, 57. (j) Fleming, I. In Comprehensive Organic Synthesis,
Vol. 2; Trost, B. M.; Fleming, I.; Paquette, L. A., Eds.;
Pergamon: Oxford, 1991, 563. (k) Langkopf, E.; Schinzer,
D. Chem. Rev. 1995, 95, 1375. (l) Brook, M. A. Silicon in
Organic, Organometallic and Polymer Chemistry; Wiley:
New York, 2000. (m) Chabaud, L.; James, P.; Landais, Y.
Eur. J. Org. Chem. 2004, 3173.
In general it could be indicated that Z/E ratios are lower
than those cases previously observed for the synthesis of
the simple Z-olefins.9 This loss of stereoselectivity could
be explained as a consequence of the high steric require-
ment of the -CH2SiMe3 group. This fact is in accordance
with the previous results.9 So, when the size of the R sub-
stituents that occupied the same equatorial position in the
transition state than the -CH2SiMe3 group was increased
the diastereoselection was also decreased.
(2) (a) For reviews concerning the synthesis of allylsilanes, see:
Sarkar, T. K. Synthesis 1990, 969. (b) Sarkar, T. K.
Synthesis 1990, 1101. (c) To see some examples of the
synthesis of E-allylsilanes: Tanigawa, Y.; Fuse, Y.;
Murahashi, S.-I. Tetrahedron Lett. 1982, 23, 557.
(d) Bhushan, V.; Lohray, B. B.; Enders, D. Tetrahedron Lett.
1993, 34, 5067. (e) Marumoto, S.; Kuwajima, I. J. Am.
Chem. Soc. 1993, 115, 9021. (f) Suginome, M.; Matsumoto,
A.; Ito, Y. J. Am. Chem. Soc. 1996, 118, 3061.
(g) Hanamoto, T.; Sugino, A.; Kikukawa, T.; Inanaga, J.
Bull. Soc. Chim. Fr. 1997, 134, 391. (h) Kamachi, T.;
Kuno, A.; Matsuno, C.; Okamoto, S. Tetrahedron Lett.
2004, 45, 4677. (i) Hodgson, D. M.; Fleming, M. J.;
Stanway, S. J. J. Am. Chem. Soc. 2004, 126, 12250.
(3) Ilio, H.; Ishii, M.; Tsukamoto, T. Tetrahedron Lett. 1988, 29,
5965.
(4) Desponds, O.; Franzini, L.; Schlosser, M. Synthesis 1997,
150.
(5) (a) Fleming, I.; Sarkar, A. K. J. Chem. Soc., Chem. Commun.
1986, 1199. (b) Fleming, I.; Gil, S.; Sarkar, A. K. J. Chem.
Soc., Perkin Trans. 1 1992, 3351.
(6) (a) Obora, Y.; Tsuji, Y.; Kobayashi, M.; Kawamura, T. J.
Org. Chem. 1995, 60, 4647. (b) Landais, Y.; Planchenault,
D.; Weber, V. Tetrahedron Lett. 1994, 35, 9549.
(7) Concellón, J. M.; Bernad, P. L.; Pérez-Andrés, J. A. Angew.
Chem. Int. Ed. 1999, 38, 2384.
On the other hand, the reaction of SmI2 with aromatic O-
acetylchlorohydrin 3h took place with high E-selectivity
instead of Z-selectivity (Scheme 5). One possible mecha-
nism accounting for this elimination selectivity could
involve a non-concerted elimination reaction.18 So, the
successive generation of a benzylic radical and a benzylic
anion intermediate would undergo a b-elimination pro-
cess without the formation of the cyclic chelate I due to its
higher stability when compare with an aliphatic anion. In
addition, in this case, the b-elimination reaction is more
favored due to the C–C double bond formed being conju-
gated with the phenyl ring.19 Thus a 1,2-elimination pro-
cess takes place to afford the thermodynamically more
stable E-alkene rather than the chelation-controlled prod-
uct with Z-configuration. This modification in the relative
configuration is in accordance with other previously
described b-elimination reactions promoted by SmI2 in
which a C–C double bond conjugated with a phenyl group
is obtained.9,20
(8) Concellón, J. M.; Bernad, P. L.; Bardales, E. Org. Lett. 2001,
3, 937.
(9) Concellón, J. M.; Rodríguez-Solla, H.; Simal, C.; Huerta, M.
Org. Lett. 2005, 7, 5833.
(10) (a) a-Chloroaldehydes can be easily obtained, see: Halland,
N.; Braunton, A.; Bachmann, S.; Marigo, M.; Jørgensen, K.
A. J. Am. Chem. Soc. 2004, 126, 4790. (b) a-Chlorination
of a-alkylated aldehydes was carried out using sulfuryl
chloride: Stevens, C. L.; Farkas, E.; Gillis, B. J. Am. Chem.
Soc. 1954, 76, 2695.
(11) General Procedure for the Synthesis of Compounds 3.
Trimethylsilylmethyllithium (12 mL, 1.0 M solution in
pentane) was added at –85 °C to a solution of the
corresponding a-chloroaldehyde 1 (10 mmol) in THF (10
mL). After stirring for 2 h, the reaction mixture was
quenched by addition of sat. aq NH4Cl (10 mL). Standard
work-up provided crude 3-chloro-1-(trimethylsilyl)alkan-2-
ols 2. The O-acetylation reaction was carried out by
treatment of the corresponding crude 3-chloro-1-
(trimethylsilyl)alkan-2-ols 2 (1 mmol) with Et3N (10 mL),
Ac2O (10 mL) and a catalytic amount of DMAP (5 mg). The
reaction mixture was stirred for 12 h at r.t., then the reaction
was quenched with ice-cold H2O (30 mL). The organic
material was extracted with CH2Cl2. The combined extracts
were dried over Na2SO4 and the solvent was removed under
reduced pressure affording compounds 3 which were
utilized without further purification. Compounds 3 were
obtained as a mixture of diastereoisomers (roughly 1:1),
after column chromatography (hexane–EtOAc, 5:1).
(12) The solution of SmI2 in THF was rapidly obtained by
reaction of diiodomethane with samarium powder in the
presence of sonic waves: Concellón, J. M.; Rodríguez-Solla,
H.; Bardales, E.; Huerta, M. Eur. J. Org. Chem. 2003, 1775.
OAc
OAc
SmI2
SmI2
Ph
SiMe3
Ph
SiMe3
4 h
3h
∆
∆
SmI2
5 h
Scheme 5 Mechanistic proposal for the conversion of 3h to 4h
In conclusion, we have described a general synthesis of
Z-allylsilanes with good stereoselectivity through a SmI2-
promoted 1,2-elimination process on easily available O-
acetyl chlorohydrins.
Acknowledgment
We thank the Ministerio de Educación y Ciencia (CTQ2004-1191/
BQU) for financial support. J.M.C. thanks Carmen Fernández-
Flórez for her time. H.R.S. and C.S. thank the Ministerio de
Educación y Ciencia for a Ramón y Cajal Contract (Fondo Social
Europeo) and a predoctoral FPI fellowship, respectively. Our
thanks to Euan C. Goddard for his revision of the English.
References and Notes
(1) (a) Chan, T. H.; Fleming, I. Synthesis 1979, 761.
(b) Magnus, P. Aldrichimica Acta 1980, 13, 43.
(c) Fleming, I. Chem. Soc. Rev. 1981, 10, 83. (d) Sakurai,
H. Pure Appl. Chem. 1982, 54, 1. (e) Schinzer, D. Synthesis
1988, 263. (f) Hosomi, A. Acc. Chem. Res. 1988, 21, 200.
(g) Colvin, E. W. Silicon Reagents in Organic Synthesis;
Springer: Berlin, 1988. (h) Sakurai, H. Synlett 1989, 1.
(i) Fleming, I.; Dunogues, J.; Smithers, R. Org. React. 1989,
Synlett 2007, No. 1, 75–78 © Thieme Stuttgart · New York

78
J. M. Concellón et al.
LETTER
(13) General Procedure for the Synthesis of Allylsilanes 4.
A solution of SmI2 (1.2 mmol) in THF (12 mL) was added
dropwise, under a nitrogen atmosphere, to a stirred solution
of the corresponding starting material 3 (0.4 mmol) at r.t.
The reaction mixture was then refluxed for 8 h. After this
time, it was quenched with aq HCl (0.1 M, 10 mL). The
organic material was extracted with Et2O. The combined
extracts were dried over Na2SO4 and the solvent was
removed under reduced pressure affording crude compounds
4 which were purified by short-column chromatography
(silica gel, pentane as eluent). Spectroscopical data for the
compounds 4 which are not described in the literature are
given here.
for C14H22Si [M+]: 218.1491; found: 218.1487. IR (neat):
3004, 2957, 1248, 856, 698 cm–1.
Trimethyl[(E/Z)-3-methyldodec-2-enyl]silane (4i):
Rf = 0.90 (pentane). 1H NMR (300 MHz, CDCl3): d = 5.17–
5.08 (m, 2 H), 2.06–2.03 (m, 2 H), 1.99–1.86 (m, 4 H), 1.84–
1.82 (m, 2 H), 1.67 (s, 3 H), 1.52 (s, 3 H), 1.39–1.12 (m, 28
H), 0.89–0.85 (m, 6 H), –0.02 (s, 9 H). 13C NMR (75 MHz,
CDCl3): d = 133.1 (C), 132.6 (C), 119.9 (CH), 119.8 (CH),
39.8 (CH2), 31.9 (2 ꢀ CH), 31.4 (CH2), 29.6 (2 ꢀ CH2), 29.5
(2 ꢀ CH2), 29.3 (2 ꢀ CH2), 29.2 (CH2), 28.2 (CH2), 27.9
(CH2), 25.5 (CH2), 23.3 (CH3), 22.6 (2 ꢀ CH2), 18.4 (CH2),
18.2 (CH2), 15.6 (CH3), 14.0 (2 ꢀ CH3), –1.80 (3 ꢀ CH3),
–1.80 (3 ꢀ CH3). MS (70 eV): m/z (%) = 254 (6) [M+], 180
(2), 73 (100), 59 (5), 41 (6). HRMS: m/z calcd for C16H34Si
[M+]: 254.2430; found: 254.2426. IR (neat): 2925, 2855,
1458, 1247, 857 cm–1.
(Z)-Dodeca-2,11-dienyltrimethylsilane (4d): Rf = 0.83
(pentane). 1H NMR (300 MHz, CDCl3): d = 5.80 (ddt,
J = 17.0, 10.2, 6.7 Hz, 1 H), 5.40–5.32 (m, 1 H), 5.28–5.21
(m, 1 H), 4.98 (ddt, J = 17.0, 2.3, 1.6 Hz, 1 H), 4.91 (ddt,
J = 10.2, 2.3, 1.1 Hz, 1 H), 2.08–1.97 (m, 4 H), 1.47 (d,
(14) Hsiao, C.-N.; Shechter, H. Tetrahedron Lett. 1982, 23, 1963.
(15) Shiragami, H.; Kawamoto, T.; Imi, K.; Matsubara, S.;
Utimoto, K.; Nozaki, H. Tetrahedron 1988, 44, 4009.
(16) Other six-membered-ring transition-state models have been
proposed to explain the selectivity in other reactions of
SmI2: (a) Molander, G. A.; Etter, J. B.; Zinke, P. W. J. Am.
Chem. Soc. 1987, 109, 453. (b) Urban, D.; Skrydstrup, T.;
Beau, J. M. J. Org. Chem. 1998, 63, 2507. (c) Concellón, J.
M.; Pérez-Andrés, J. A.; Rodríguez-Solla, H. Angew. Chem.
Int. Ed. 2000, 39, 2773. (d) Concellón, J. M.; Pérez-Andrés,
J. A.; Rodríguez-Solla, H. Chem. Eur. J. 2001, 7, 3062.
(e) Concellón, J. M.; Rodríguez-Solla, H. Chem. Soc. Rev.
2004, 33, 599; and references 7–9.
(17) To see previous works about the g-effect of the silicon atom,
see: (a) Sommer, L. H.; Dorfman, E.; Goldberg, G. M.;
Whitmore, F. C. J. Am. Chem. Soc. 1946, 68, 488.
(b) Shiner, V. J. Jr.; Ensinger, M. W. J. Am. Chem. Soc.
1986, 108, 842. (c) Davidson, E. R.; Shiner, V. J. Jr. J. Am.
Chem. Soc. 1986, 108, 3135.
(18) This is consistent with other previously reported SmI2-
mediated b-elimination methodologies with Z-selectivity
(see ref. 7–9). So, when aryl-substituted olefins were
obtained an enhancement of the E-stereoisomer was
observed.
(19) An isomerization process of the Z-phenyl alkene to the more
stable E-isomer cannot be discarded under this reaction
conditions.
J = 8.5 Hz, 2 H), 1.43–1.25 (m, 10 H), 0.01 (s, 9 H). 13
C
NMR (75 MHz, CDCl3): d = 139.1 (CH), 127.6 (CH), 125.1
(CH), 114.0 (CH2), 33.7 (CH2), 29.7 (CH2), 29.3 (CH2), 29.3
(CH2), 29.0 (CH2), 28.8 (CH2), 27.0 (CH2), 18.3 (CH2), –1.9
(3 ꢀ CH3). MS (70 eV): m/z (%): 238 (3) [M+], 73 (100), 59
(11), 41 (11). IR (neat): 2925, 2854, 1465, 1378 cm–1. Anal.
Calcd for C15H30Si: C, 75.54; H, 12.68. Found: C, 75.22; H,
12.90.
Trimethyl[(2Z,8Z)-undeca-2,8-dienyl]silane (4e): Rf = 0.85
(pentane). 1H NMR (300 MHz, CDCl3): d = 5.44–5.22 (m, 4
H), 2.06–1.97 (m, 6 H), 1.47 (d, J = 8.3 Hz, 2 H), 1.39–1.34
(m, 4 H), 0.96 (t, J = 7.5 Hz, 3 H), 0.00 (s, 9 H). 13C NMR
(75 MHz, CDCl3): d = 131.5 (CH), 129.2 (CH), 127.5 (CH),
125.3 (CH), 29.5 (CH2), 29.4 (CH2), 27.0 (CH2), 26.9 (CH2),
20.5 (CH2), 18.3 (CH2), 14.3 (CH3), –1.9 (3 ꢀ CH3). MS (70
eV): m/z (%) = 224 (2) [M+], 150 (18), 142 (21), 121 (16), 73
(100), 59 (36), 45 (38). HRMS: m/z calcd for C13H25Si
[M+ – Me]: 209.1726; found: 209.1729. IR (neat): 3007,
2929, 1462, 1248, 855 cm–1.
Trimethyl[(E/Z)-4-phenylpent-2-enyl]silane (4g): Rf = 0.65,
0.60 (hexane). 1H NMR (300 MHz, CDCl3): d = 7.37–7.21
(m, 10 H), 5.55–5.43 (m, 4 H), 3.75 (q, J = 7.5 Hz, 1 H),
3.51–3.46 (m, 1 H), 1.68–1.49 (m, 4 H), 1.40 (t, J = 6.0 Hz,
3 H), 1.38 (t, J = 6.8 Hz, 3 H), 0.06 (s, 9 H), 0.05 (s, 9 H).
13C NMR (75 MHz, CDCl3): d = 147.0 (C), 146.8 (C), 133.6
(CH), 132.6 (CH), 128.3 (2 ꢀ CH), 128.2 (2 ꢀ CH), 127.1
(2 ꢀ CH), 126.9 (2 ꢀ CH), 125.7 (CH), 125.7 (CH), 125.1
(CH), 124.6 (CH), 42.4 (CH), 36.8 (CH), 22.5 (CH3), 21.7
(CH3), 18.5 (2 ꢀ CH2), –1.80 (3 ꢀ CH3), –1.90 (3 ꢀ CH3). MS
(70 eV): m/z (%) = 218 (41) [M+], 144 (20), 135 (23), 129
(19), 105 (16), 73 (100), 59 (16), 45 (25). HRMS: m/z calcd
(20) A similar behavior has been observed in other SmI2-
promoted processes when benzylic radicals are generated:
Davies, S. G.; Rodríguez-Solla, H.; Tamayo, J. A.; Cowley,
A. R.; Concellón, C.; Garner, A. C.; Parkes, A. L.; Smith, A.
D. Org. Biomol. Chem. 2005, 3, 1435.
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