Page 457 - Advanced Organic Chemistry Part B - Reactions & Synthesis

430 the less hindered face of the carbonyl group. 191 However, these conditions frequently
promote equilibration of the alcohol stereoisomers.
CHAPTER 5
Reduction of
Carbon-Carbon Multiple Al
Bonds, Carbonyl O O
Groups, and Other CH 3 C C
Functional Groups H R
CH 3 R

Recently, enantioselective procedures involving chiral catalysts have been
developed. The combination of BINOL and Al CH can achieve 80% e.e. in the
3 3
reduction of acetophenone. 192 Compound J is also an effective catalyst. 193

O
Al OCH(CH )
3 2
N
C F
SO 2 8 17
J
Certain lanthanide alkoxides, such as t-BuOSmI , have also been found to catalyze
2
hydride exchange between alcohols and ketones. 194 Isopropanol can serve as the
reducing agent for aldehydes and ketones that are thermodynamically better hydride
acceptors than acetone.

CH CHCH 3
3
OH
O N CH O O N CH OH
2
2
2
t-BuOSmI 2
94%
Samarium metal in isopropanol also achieves reduction. 195 Like the Meerwein-
Pondorff-Verley procedure, these conditions are believed to be under thermodynamic
control and the more stable stereoisomer is the main product. 196
Another reduction process, catalyzed by iridium chloride, is characterized by
very high axial:equatorial product ratios for cyclohexanones and apparently involves
hydride transfer from isopropanol. 197

IrCl , HCl
4
(CH ) C (CH O) P, H O (CH ) C
3 3
3 3
2
3
3
O (CH ) CHOH OH
3 2
Formic acid can also act as a donor of hydrogen, and the driving force in this
case is the formation of carbon dioxide. A useful application is the Clark-Eschweiler
191
F. Nerdel, D. Frank, and G. Barth, Chem. Ber., 102, 395 (1969).
192
E. J. Campbell, H. Zhou, and S. T. Nguyen, Angew. Chem. Int. Ed. Engl., 41, 1020 (2002).
193 T. Ooi, H. Ichikawa, and K. Maruoka, Angew. Chem. Int. Ed. Engl., 40, 3610 (2001).
194
J. L. Namy, J. Souppe, J. Collin, and H. B. Kagan, J. Org. Chem., 49, 2045 (1984).
195 S. Fukuzawa, N. Nakano, and T. Saitoh, Eur. J. Org. Chem., 2863 (2004).
196 D.A. Evans, S. W. Kaldor, T. K. Jones, J. Clardy, and T. J. Stout, J. Am. Chem. Soc., 112, 7001 (1990).
197
E. L. Eliel, T. W. Doyle, R. O. Hutchins, and E. C. Gilbert, Org. Synth., 50, 13 (1970).