the photoinduced metalation processes of nonactivated C-Cl
bonds by SmI2 have been recently reported.11
100 W), alkenes 2 were obtained with total or very high
stereoselectivity after 8 h of reaction (Scheme 1). When this
In particular, SmI2 has been used to promote elimination
reactions to afford C-C double bonds with high stereose-
lectivity.12 For instance, our group has previously described
the preparation of vinyl halides,13 vinyl silanes,14 R,â-
unsaturated esters,15 amides,16 or ketones17 by using this
reagent. In all these preceding examples, the â-elimination
reaction was triggered by the metalation of the activated
C-halogen bond with SmI2.
Scheme 1. Synthesis of Alkenes 2
In this paper, we describe an efficient and highly stereo-
selective preparation of alkenes from O-acetylated chloro-
hydrins, in which the â-elimination reaction is initiated by
metalating the nonactivated C-Cl bond with SmI2 in the
presence of visible light. To the best of our knowledge, this
is the first method to promote 1,2-elimination reactions by
treating chlorinated compounds in which the C-Cl bond is
nonactivated with SmI2. Although this elimination process
seems appropriate to be also performed on O-acetyl bromo-
hydrins, the use of O-acetyl chlorohydrins 1 presents some
advantages: O-acetyl chlorohydrins are easier to prepare and,
in general, more accessible than the equivalent bromo
derivatives.18
The starting chlorohydrins 1 were prepared by subsequent
treatment of several R-chloroaldehydes19 with different
Grignard reagents and acetyl chloride.20
Thus, when a mixture of O-acetyl chlorohydrins 1 and
SmI2 (0.1 M THF solution) was refluxed in THF in the
presence of visible light (five household tungsten lamps ×
process was carried out in the absence of light no reaction
took place.
This transformation is general, and aliphatic (linear,
branched, or cyclic) alkenes 2a-f were obtained with total
or very high (Z)-selectivity (Table 1, entries 1-6). R1 and
Table 1. Synthesis of Alkenes 2 by Using SmI2
entry
2
R1
R2
Z/Ea
yieldb
1
2
3
4
5
6
7
8
9
10
2a
2b
2c
2d
2e
2f
2g
2h
2i
n-C6H13
n-C6H13
n-C6H13
n-Pr
n-Pr
i-Pr
-(CH2)5-
Ph
Ph
Et
>98/2
>98/2
91/9
>98/2
94/6
90/10
-
8/92
20/80
-
53
72
51
65
56
87
79
60
67
65
n-Bu
s-Buc
n-C10H21
Cy
n-C8H17
n-Buc
Et
Cy
H
2j
Ph
(9) (a) Kagan, H. B. Tetrahedron 2003, 59, 10351-10372. (b) Steel, P.
G. J. Chem. Soc., Perkin Trans. 1 2001, 2727-2751. (c) Krief, A.; Laval,
A. M. Chem. ReV. 1999, 99, 745-777. (d) Molander, G. A.; Harris, C. R.
Tetrahedron 1998, 54, 3321-3354. (e) Molander, G. A.; Harris, C. R. Chem.
ReV. 1996, 96, 307-338. (f) Molander G. A. In Organic Reactions; Paquette,
L. A., Ed.; Wiley: New York, 1994; Vol. 46, pp 211-367. (g) Molander,
G. A. Chem. ReV. 1992, 92, 29-68. (h) Soderquist, J. A. Aldrichimica Acta
1991, 24, 15-23.
a Z/E ratio was determined by GC-MS and/or 300 MHz 1H NMR
analysis of the crude products 2. b Isolated yield after column chromatog-
raphy based on compound 1. c s-BuLi and n-BuLi were used, instead of
Grignard reagents, for the synthesis of starting materials 1c and 1g,
respectively.
R2 can be varied using diverse R-chloroaldehydes and
Grignard derivatives, respectively.
(10) Reaction of samarium diiodide with nonactivated C-Cl bonds is
generally difficult to achieve, and normally no reaction is observed. See
ref 9b.
When aromatic O-acetyl chlorohydrins 1h,i were used, (E)-
alkenes were obtained with high stereoselectivity (Table 1,
entries 8 and 9). In addition, this method can be also
employed to obtain terminal alkenes such as 2j (Table 1,
entry 10).
(11) (a) Prasad, E.; Knettle, B. W.; Flowers, R. A., II. Chem.-Eur. J.
2005, 11, 3105-3112. (b) Sumino, Y.; Harato, N.; Tomisaka, Y.; Ogawa,
A. Tetrahedron 2003, 59, 10499-10508. (c) Molander, G. A.; Alonso-
Alija, C. J. Org. Chem. 1998, 63, 4366-4373. (d) Molander, G. A.; Wolfe,
C. N. J. Org. Chem. 1998, 63, 9031-9036. (e) Ogawa, A.; Sumino, Y.;
Nanke, T.; Ohya, S.; Sonoda, N.; Hirao, T. J. Am. Chem. Soc. 1997, 119,
2745-2746. (f) Skene, W. G.; Scaiano, J. C.; Cozens, F. L. J. Org. Chem.
1996, 61, 7918-7921.
The Z/E ratio was determined on the crude reaction
products by 1H NMR (300 MHz) spectroscopy and/or GC-
MS. The (Z)- or (E)-stereochemistry of the C-C double bond
in alkenes 2 was assigned on the basis of the value of the
1H NMR coupling constants between the olefinic protons of
compounds 2a-f and 2h,i and/or by comparison with NMR
data previously reported in the literature for 2b and 2g-i
(see Supporting Information). Two aspects of this process
are worthy of mention: (a) although the O-acetyl chloro-
hydrins 1 were synthesized and used as mixtures of diaste-
reoisomers (roughly 1:1), the corresponding alkenes 2 were
obtained with total or high stereoselectivity and (b) in terms
of cost, safety, and cleanliness, no cosolvents are necessary
for these reactions.11c
(12) For a review of â-elimination reactions promoted by SmI2, see:
Concello´n, J. M.; Rodr´ıguez-Solla, H. Chem. Soc. ReV. 2004, 33, 599-
609.
(13) Concello´n, J. M.; Bernad, P. L.; Pe´rez-Andre´s, J. A. Angew. Chem.
1999, 111, 2528-2530; Angew. Chem., Int. Ed. 1999, 38, 2384-2386.
(14) Concello´n, J. M.; Bernad, P. L.; Bardales, E. Org. Lett. 2001, 3,
937-939.
(15) Concello´n, J. M.; Pe´rez-Andre´s, J. A.; Rodr´ıguez-Solla, H. Angew.
Chem. 2000, 112, 2866-2868; Angew. Chem., Int. Ed. 2000, 39, 2773-
2775.
(16) Concello´n, J. M.; Pe´rez-Andre´s, J. A.; Rodr´ıguez-Solla, H. Chem.-
Eur. J. 2001, 7, 3062-3068.
(17) Concello´n, J. M.; Huerta, M. Tetrahedron Lett. 2003, 44, 1931-
1934.
(18) Addition of Grignard derivatives to R-bromoaldehydes afforded the
corresponding epoxide (Darzens’-type reaction).
(19) R-Chloroaldehydes can be easily obtained by chlorination of
aldehydes with sulfuryl chloride: Stevens, C. L.; Farkas, E.; Gillis, B. J.
Am. Chem. Soc. 1954, 76, 2695-2698.
(20) Barluenga, J.; Yus, M.; Concello´n, J. M.; Bernad, P. J. Chem. Res.,
Synop. 1980, 41; J. Chem. Res., Miniprint 1980, 677-692.
The acetyl group in compound 1 is believed to play a key
role on the observed reaction outcome. Accordingly, when
5834
Org. Lett., Vol. 7, No. 26, 2005
Concellon, Jose M.
