A. T. Tran et al. / Tetrahedron Letters 50 (2009) 1817–1819
1819
tions.37 We are pursuing studies to determine the mechanisms at
work in this reduction method.
19. Aramini, A.; Brinchi, L.; Germani, R.; Savelli, G. Eur. J. Org. Chem. 2000, 1793–
1797.
20. Chum, P. W.; Wilson, S. E. Tetrahedron Lett. 1976, 15–16.
In summary, we have developed a very simple and robust, gen-
eral method for the reduction of alkenes and alkynes. The method
is convenient, and does not require an external source of hydro-
gen gas. Significantly, the procedure works well in a variety of
solvents and with a broad range of unsaturated hydrocarbons.
We are currently conducting studies to determine the general
applicability of this reaction to other functional groups in various
solvents.
21. Ashby, E. C.; Lin, J. J. Tetrahedron Lett. 1977, 4481–4484.
22. Ashby, E. C.; Lin, J. J. J. Org. Chem. 1978, 43, 2567–2572.
23. Tour, J. M.; Cooper, J. P.; Pendalwar, S. L. J. Org. Chem. 1990, 55, 3452–3453.
24. Tour, J. M.; Pendalwar, S. L. Tetrahedron Lett. 1990, 31, 4719–4722.
25. Wang, J. Y.; Song, G. H.; Peng, Y. Q.; Zhu, Y. D. Tetrahedron Lett. 2008, 49, 6518–
6520.
26. Mirza-Aghayan, M.; Boukherroub, R.; Bolourtchian, M.; Hosseini, M.
Tetrahedron Lett. 2003, 44, 4579–4580.
27. Isolation scale procedure: A 250 mL round-bottomed flask with stir bar is
charged in open air with the Pd/C catalyst, the alkene (10 mmol), and 50 mL of
isopropyl alcohol (IPA). The flask is clamped over a mechanical stirrer, and the
contents are stirred. Acetic acid (20 mmol) is added in a single portion via
pipette. Powdered NaBH4 (40 mmol) is added in a single portion directly to the
stirring heterogeneous solution (Note: Addition of the NaBH4 causes the rapid
evolution of small hydrogen gas bubbles). The contents of the reaction flask are
left to stir in open air at room temperature for 15 min. Workup is conducted by
quenching the reaction mixture with several mLs of 0.1 M HCl until no further
hydrogen evolution is observed (Note: Quenching produces considerable heat;
it is advisable to cool the contents with an ice bath during quenching). The
solution is then adjusted to a pH of approximately 10 using NaOH and filtered
to remove the Pd/C catalyst. n-Pentane (40 mL) is added to the filtrate, which is
then extracted with DI water (3 Â 40 mL). The aqueous portions are then
combined and reextracted with n-pentane (1 Â 40 mL). The organic portions
are combined, dried over MgSO4, and filtered. The product alkanes are obtained
in pure form by removal of the solvent under reduced pressure. Reactions are
typically analyzed by GC/MS and/or 1H NMR.
28. Under solvent-free, open-air conditions, the combination of sodium
borohydride and palladium catalyst produces rapid hydrolysis of the
borohydride with release of hydrogen gas. In the absence of solvent, the heat
evolved from the hydrolysis is sufficient to cause combustion of the hydrogen
gas. Thus, the procedure described above should only be performed following
the indicated order of addition and with the catalyst suspended in the selected
solvent. In our experience with laboratory scale experiments, the palladium
catalyst could be safely filtered from the reaction mixture after quenching the
reaction with aqueous HCl.
Acknowledgments
We wish to acknowledge Pacific University and the M. J. Mur-
dock Charitable Trust for support.
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