Page 473 - Advanced Organic Chemistry Part B - Reactions & Synthesis

446 O
H CH OCH Ph
CH 2 2
O HC O
CHAPTER 5
O
Reduction of O O
Carbon-Carbon Multiple PhCH OCH H
2 2
Bonds, Carbonyl
Groups, and Other
Functional Groups TiCl 3
Zn-Cu
H CH OCH Ph
O 2 2
O
O
O
PhCH OCH H
2
2
Ref. 247
The double bonds were reduced to the give the saturated compounds, so the double-
bond configuration was not an immediate issue. It appears, however, that the E-double
bonds are formed. The debenzylated derivatives of propan-1,2,3-triol occur as lipid
components in various prokaryotes (archaebacteria) that grow under extreme thermal
conditions.
Under other conditions, reduction leads to diols. Reductive coupling to diols can
be done using magnesium amalgam 248 or zinc dust. 249

O O CH 3
OH Mg–Hg OH
Mg–Hg
O CH 3 CCH CH CCH 3
2
2
TiCl 4 HO TiCl 4 CH 3 OH
95% 81%
The most general procedures are based on low-valent titanium. Good yields of diols
are obtained from aromatic aldehydes and ketones by adding catechol to the TiCl -Mg
3
reagent prior to coupling. 250

O OH OH
TiCl 3 , Mg
PhCCH 3 THF, catechol PhC CPh
CH 3 CH 3
95%

Both unsymmetrical alkenes and diols can be prepared by applying these methods
to mixtures of two different carbonyl compounds. An excess of one component can be
used to achieve a high conversion of the more valuable reactant. A mixed reductive

247
T. Eguchi, K. Ibaragi, and K. Kakinuma, J. Org. Chem., 63, 2689 (1998).
248 E. J. Corey, R. L. Danheiser, and S. Chandrasekaran, J. Org. Chem., 41, 260 (1976).
249 A. Furstner, A. Hupperts, A. Ptock, and E. Janssen, J. Org. Chem., 59, 5215 (1994).
250
N. Balu, S. K. Nayak, and A. Banerji, J. Am. Chem. Soc., 118, 5932 (1996).