THIS REACTION IS STRONGLY pH DEPENDENT AND
BEST PROCEEDS AT A pH OF 8-9. !!!!!

From Agric. Biol. Chem., Volume 50, yr 1986, page 1261

"Reductive C3-Homologation of Substituted Benzaldehydes by
Fermenting Bakers' Yeast

...

... A unique reaction catalyzed by Bakers' Yeast is the reductive C-C bond formation in
benzaldehyde that results in the formation of 1-phenylpropane-1,2-diol [ref 3]. This reaction is
supposed to involve the attack of pyruvic acid, which is formed from sugars through a well known
pathway, by benzaldhyde to give phenyl-1-hydroxy-2-propanone [ref 4]. This ketol is considered to
be reduced by alcohol dehydrogenase of the yeast to give the
diol. ...

...

Reduction of aldehydes by fermenting yeast. General procedure. To 50 mL of tap water, 12.5 g
of dry yeast and 10 g glucose were added, followed by stirring
at room temperature for 10 minutes. Then a solution of aldehyde 1 (about 600 mg) in 1 mL of
ethanol was added to the suspension of fermenting yeast with stirring. After 1 hour yeast (6.2 g)
and glucose (5 g) were added to the reaction mixture, followed by stirring for an additional 3.5
hours. The reaction mixture was then poured into a beaker containing 35 grams of celite and
extracted with 100 mL of ethyl acetate three times. The combined organic layer was dried over
anhydrous Na2SO4. The solvent removed under reduced pressure to give an oil consisting of
benzylic alcohol 3, 1-arylpropane-1,2 diol 3, and in
some cases, 1-aryl-1-hydroxy-2-propanone 4. ...

Table II. Yields and Steroselectivities of propanediols (a)

_____________________________________________________________
Substrate______Yield %____...

______________________________________________________________
H______________30
p-OMe__________22
p-Me____________28
p-Cl____________27
p-F_____________26
p-NO2__________14
o-Me____________7
o-Cl_____________32
o-F_____________30
m-F____________31
CF3(e)__________0
_________________________
(a) Reactions were carried out in tap water at room
temperature ... (e) All of the o-, m-
p-substituted isomers gave no diols."
_________________

Полученный фенилпропандиол легко переводится в фенилацетон стандартными методами (см. Окисление пропенилбензолов)