3858
R. Bejot et al. / Tetrahedron Letters 48 (2007) 3855–3858
6. Barma, D. K.; Baati, R.; Valleix, A.; Mioskowski, C.;
Falck, J. R. Org. Lett. 2001, 3, 4237.
carbenoid intermediate 7, which is quenched with water
to lead to chloroolefins 2. a-Chloromethyl ketone 13 is
likely to be reduced under aqueous conditions to give
chromium(III)-enolate 19, which undergoes either a b-
elimination to give alkynes 3 or a hydrolysis to generate
methyl ketone 14. Alternatively, enol 19 may be formed
through the rehybridization of 1-chloro-1,1-bis-chro-
mium(III) methylcarbinol carbenoid 17 and a subse-
quent 1,2 hydride migration (17!18!19).
7. (a) Bejot, R.; Tisserand, S.; Reddy, L. M.; Barma, D. K.;
Baati, R.; Falck, J. R.; Mioskowski, C. Angew. Chem., Int.
Ed. 2005, 44, 2008; (b) Walborsky, H. M.; Duraisamy, M.
J. Am. Chem. Soc. 1984, 106, 5035; (c) Walborsky, H. M.;
Rachon, J.; Goedken, V. J. Am. Chem. Soc. 1986, 108,
7435; For an example of a postulated chromium(III)–
carbene complex, see: (d) Voges, M. H.; Romming, C.;
Tilset, M. Organometallics 1999, 18, 529.
8. (a) Fritsch, P. Liebigs Ann. Chem. 1894, 279, 319; (b)
Buttenberg, W. P. Liebigs Ann. Chem. 1894, 279, 324; (c)
Wiechell, H. Liebigs Ann. Chem. 1894, 279, 337.
9. Mykhalichko, B. M.; Temkin, O. N.; Mys’kiv, M. G.
Russ. Chem. Rev. 2000, 69, 957.
10. Trichloromethylcarbinols were described to give 1-chloro-
1(Z)-alkenes via (E)-halovinylidene chromium carbenoids
with CrCl2 in anhydrous THF, see: Baati, R.; Barma, D.
K.; Falck, J. R.; Mioskowski, C. Tetrahedron Lett. 2002,
43, 2183.
11. Procedure: A suspension of CrCl2 (1.2 mmol, 6 equiv) in
oxygen- and water-free THF (1 mL) was added via a
syringe to a solution of trichloromethyl carbinol 12
(0.2 mmol, 1 equiv) in THF (1 mL), under an argon
atmosphere at ambient temperature. After 3 h at ambient
temperature, an aliquote of the reaction mixture was
filtered through a small pad of SiO2 and GC–MS analysis
In summary, we have demonstrated that trichloromethyl
alkanes and carbinols undergo chromium(II)-mediated
transformations to chromium(III)–carbene (8 and 16)
and –carbyne complexes (10 and 18). We do not demon-
strate the predominance of a single reaction mechanism
to the exclusion of all other alternatives, but competitive
mechanisms have been proposed which account for the
nature of the observed products: after further transfor-
mations, carbenes afford various alkenes (2 and 4), alky-
nes (3), and ketones (13 and 14).
Acknowledgments
`
´ ´ ´ `
We are grateful to the Ministere delegue a l’Enseigne-
´
`
indicated a complete conversion to a-chloromethyl
ment superieur et a la Recherche, the CNRS, the Institut
de Recherche Pierre Fabre, the Robert A. Welch Foun-
dation and the NIH (GM31278, DK38226) for their
financial support of this work.
ketones 13. H2O (1 mL) was added to the reaction
mixture. After 10 min (for 12a) or 3 h (for 12c) at ambient
temperature, the reaction was quenched with 5% HCl and
extracted with Et2O (3·). The combined ethereal extracts
were washed with brine, dried over MgSO4, filtered
through a small pad of SiO2, and analyzed by GC–MS,
which indicated a complete conversion to methylketones
Supplementary data
14. Alternatively
a suspension of CrCl2 (0.6 mmol,
Supplementary data associated with this article can be
3 equiv) in water (1 mL) was added via a syringe at room
temperature to a solution of a-chloromethyl ketones 13
(0.2 mmol, 1 equiv) in oxygen-free THF (1 mL), under an
argon atmosphere. After 10 min to 3 h at ambient
temperature, the reaction was quenched with 5% HCl
and extracted with Et2O (3·). The combined ethereal
extracts were washed with brine, dried over MgSO4,
filtered through a small pad of SiO2, and analysis by GC–
MS indicated a complete conversion to methyl ketones 14.
12. Chromium(II) reduction of trichloromethyl carbinols in
aqueous DMF was previously described, see: Wolf, R.;
Steckhan, E. J. Chem. Soc., Perkin Trans. 1 1986, 733.
13. Procedure: A solution of CrCl2 (1.2 mmol, 6 equiv) in
H2O (1 mL) was added via a syringe at room temperature
to a solution of trichloromethylcarbinol 12 (0.2 mmol,
1 equiv) in oxygen-free THF, under an argon atmosphere.
After 3 h at ambient temperature, the reaction was
quenched with 5% HCl and extracted with Et2O (3·).
The combined ethereal extracts were washed with brine,
dried over MgSO4, filtered through a small pad of SiO2,
and analyzed by GC–MS.
References and notes
1. Baati, R.; Barma, D. K.; Falck, J. R.; Mioskowski, C. J.
Am. Chem. Soc. 2001, 123, 9196.
2. Bejot, R.; He, A.; Falck, J. R.; Mioskowski, C. Angew.
Chem., Int. Ed. 2007, 46, 1719.
3. (a) Kochi, J. K.; Davis, D. D. J. Am. Chem. Soc. 1964, 86,
5264; (b) Kochi, J. K.; Singleton, D. M. J. Am. Chem. Soc.
1968, 90, 1582; (c) Furstner, A. Chem. Rev. 1999, 99, 991;
(d) Mulzer, J.; Strecker, A. R.; Kattner, L. Tetrahedron
Lett. 2004, 45, 8867.
4. Procedure: A suspension of CrCl2 (1.2 mmol, 6 equiv) in
oxygen- and water-free THF or in H2O (1 mL) was added
via a syringe to solution of trichloroalkane 1 (0.2 mmol,
1 equiv) in THF (1 mL), under an argon atmosphere at
ambient temperature. After 12 h at ambient temperature,
the reaction was quenched with 5% HCl and extracted
with Et2O (3·). The combined ethereal extracts were
washed with brine, dried over MgSO4, filtered through a
small pad of SiO2, and analyzed by GC–MS.
14. The 1-chloro-1(Z)-alkenes described in Ref. 10 can be
obtained from trichloromethylcarbinols and CrCl2 in
aqueous conditions. However coupling adducts 2-halo-
alk-2-(Z)-en-1-ols could not be observed in the presence of
an aldehyde.
5. Baati, R.; Barma, D. K.; Krishna, U. M.; Mioskowski, C.;
Falck, J. R. Tetrahedron Lett. 2002, 43, 959.