The Journal of Organic Chemistry
Brief Communication
Scheme 1
EXPERIMENTAL SECTION
DEDICATION
■
■
Materials. The kinetic studies were carried out in dry hexanes and
THF. Hexanes were prepared by distillation and stored over molecular
sieves. THF was purified using an air-free solvent purification system.
Samarium diiodide (SmI2) was prepared by standard methods, and
iodometric titration was employed to verify concentration prior to use.6,7
{Sm[N(SiMe3)2]2(THF)2} was prepared and purified by the method
reported by Evans.16 In all subsequent experiments KI-free {Sm[N-
(SiMe3)2]2(THF)2} was used as a free-flowing powder. Bromododecane
and chlorododecane were purified using automated flash chromatog-
raphy on prepacked silica gel columns with a gradient elution of ethyl
acetate and hexanes. 3-Pentanone was used without further purification.
Kinetic Studies. Kinetic experiments were performed with a
computer-controlled stopped-flow spectrophotometer. Substrates and
{Sm[N(SiMe3)2]2(THF)2} were taken separately in airtight syringes
from a drybox and injected into the stopped-flow system. The cell box
and the drive syringes of the stopped-flow reaction analyzer were flushed
a minimum of five times with degassed solvents to make the system
oxygen-free. The drive syringes were then primed with solvent and
{Sm[N(SiMe3)2]2(THF)2} (blank) to confirm the system was air-free
and moisture-free and to verify the stability of {Sm[N(SiMe3)2]2-
(THF)2} under experimental conditions. 1-Bromododecane and 1-
chlorododecane rate studies were performed at 15 °C, whereas 3-
pentanone was performed at 5 °C. The concentrations of the substrates
were kept high (50−300 mM) relative to Sm(HMDS)2THF2
concentrations to maintain pseudo-first-order conditions. Observed
reaction rate constants were determined from exponential fitting of the
decays of 5 mM {Sm[N(SiMe3)2]2(THF)2} at 400 nm in THF and 470
nm in hexanes. Decays were obtained in the presence of increasing
substrate concentrations to provide observed rate constants, which were
then plotted against the substrate concentration, and the rate constant
was determined from the slope of the plot. The rate order of
{Sm[N(SiMe3)2]2(THF)2} was determined using fractional times
method. The THF addition study was performed by measuring reaction
rates for reduction of 50 mM 1-bromododecane in solutions of
increasing THF concentration (125 mM−2.5 M) Activation parameters
were measured by varying the temperature from 5 to 30 °C with 75 mM
1-chlorododecane and 5 mM {Sm[N(SiMe3)2]2(THF)2}.
This work is dedicated to the memory of Dr. Masangu Shabangi
(1965−2014), who provided seminal contributions on the
mechanistic study of Sm(II) reagents.
REFERENCES
■
(1) Choquette, K. A.; Flowers, R. A. Sm and Yb Reagents. In
Comprehensive Organic Synthesis, 2nd ed.; Molander, G. A., Knochel, P.,
Eds.; Elsevier: Oxford, 2014; Vol. 1, pp 279−343.
(2) Szostak, M.; Fazakerley, N. J.; Parmar, D.; Procter, D. J. Chem. Rev.
2014, 114, 5959−6039.
(3) Szostak, M.; Spain, M.; Procter, D. J. Chem. Soc. Rev. 2013, 42,
9155−9183.
(4) Procter, D. J.; Flowers, R. A., I. I.; Skrydstrup, T. Organic Synthesis
using Samarium Diiodide: A Practical Guide; RSC Publishing: Cambridge,
2010.
(5) Edmonds, D. J.; Johnston, D.; Procter, D. J. Chem. Rev. 2004, 104,
3371−3404.
(6) Sadasivam, D. V.; Choquette, K. A.; Flowers, R. A., II. J. Vis. Exp.
2013, 72, e4323.
(7) Szostak, M.; Spain, M.; Procter, D. J. J. Org. Chem. 2012, 77, 3049−
3059.
(8) Flowers, R. A., II. Synlett 2008, 1427−1439.
́
(9) Dahlen, A.; Hilmersson, G. Eur. J. Inorg. Chem. 2004, 3393−3403.
(10) Enemaerke, R. J.; Daasbjerg, K.; Skrydstrup, T. Chem. Commun.
1999, 343−344.
(11) Shabangi, M.; Sealy, J. M.; Fuchs, J. R.; Flowers, R. A., II.
Tetrahedron Lett. 1998, 39, 4429−4432.
(12) Shabangi, M.; Flowers, R. A., II. Tetrahedron Lett. 1997, 38, 1137−
1140.
(13) Halder, S.; Hoz, S. J. Org. Chem. 2014, 79, 2682−2687.
(14) Prasad, E.; Knettle, B. W.; Flowers, R. A., II. J. Am. Chem. Soc. 2004,
126, 6891−6894.
(15) Chopade, P.; Davis, T. A.; Prasad, E.; Flowers, R. A., II. Org. Lett.
2004, 6, 2685−2688.
(16) Evans, W. J.; Drummond, D. K.; Zhang, H.; Atwood, J. L. Inorg.
Chem. 1988, 27, 575−579.
́
(17) Anker, T.; Friden-Saxen, M.; Pemberton, N.; Seifert, T.; Grøtli,
M.; Luthman, K.; Hilmersson, G. Org. Lett. 2010, 12, 2210−2213.
(18) Kim, M.; Knettle, B. W.; Dahlen, A.; Hilmersson, G.; Flowers, R.
A., II. Tetrahedron 2003, 59, 10397−10402.
ASSOCIATED CONTENT
* Supporting Information
NMR spectra of products, UV−vis spectra of {Sm[N(SiMe3)2]2-
(THF)2} in THF and hexanes, decay traces, and plots of rate data.
This material is available free of charge via the Internet at http://
■
S
(19) Brady, E. D.; Clark, D. L.; Keogh, D. W.; Scott, B. L.; Watkin, J. G.
J. Am. Chem. Soc. 2002, 124, 7007−7015.
(20) Janjetovic, M.; Traff, A. M.; Anker, T.; Wettergren, J.; Hilmersson,
̈
G. Chem. Commun. 2013, 49, 1826−1818.
(21) Miller, R. S.; Sealy, J. M.; Fuchs, J. R.; Shabangi, M.; Flowers, R. A.,
II J. Am. Chem. Soc. 2000, 122, 7718−7722.
AUTHOR INFORMATION
Corresponding Author
Notes
■
(22) Farran, H.; Hoz, S. Org. Lett. 2008, 10, 865−867.
(23) Prasad, E.; Flowers, R. A., II. J. Am. Chem. Soc. 2002, 124, 6895−
6899.
(24) Choquette, K. A.; Sadasivam, D. V.; Flowers, R. A., II. J. Am. Chem.
Soc. 2010, 132, 17396−17398.
(25) Farran, H.; Hoz, S. Org. Lett. 2008, 10, 4875−4877.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
R.A.F. is grateful to the National Science Foundation (CHE
1266333) for support of the work. We thank Dr. Lawrence
Courtney and Ms. Niki Patel for helpful discussions and
suggestions.
C
dx.doi.org/10.1021/jo501819z | J. Org. Chem. XXXX, XXX, XXX−XXX