Metal complexes as phase transfer catalysts in the synthesis of O-acetylmandelonitrileстатья
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:Cyanohydrin fragments have been found in the mol
ecules of a large number of commercially important com
pounds. Pyrethroids can be mentioned as the most vivid
example.1 Cyanohydrins by themselves are versatile syn
thetic intermediates used to prepare αhydroxy acids,
αamino acids, and αamino alcohols.2—4 Since cyano
hydrins are unstable, they are mainly used in practice as
Osubstituted derivatives. Therefore, development of the
methods of synthesis of these compounds appears to be
quite topical.
Cyanohydrins can be synthesized using various sources
of cyanide ions,3 KCN or NaCN being the most conve
nient starting compounds. Stable Oacetyl derivatives of
cyanohydrins are formed under conditions we found pre
viously and used in the asymmetric synthesis of Oacetyl
cyanohydrins catalyzed by asymmetric metal complexes.5
The reaction occurs most efficiently in CH2Cl2 on treat
ment of aldehydes with KCN and Ac2O in the presence of
water additives. The conduction of reactions of organic
compounds with inorganic salts in twophase organic sol
vent—water systems offers a number of advantages. The
key advantage is the possibility of using rather concen
trated (in some cases, saturated) solutions, which pro
vides a substantial increase in the reaction rates. Two
types of these reactions are known. According to the first
one, inorganic salts are transferred into the bulk of the
organic solvent (classical phase transfer reactions), while
in the second one, organic reagents pass to the aqueous
phase. The latter case is encountered more rarely, but this
version is now under intensive research (see reviews6,7).
In this study, we attempted to prepare the Oacetyl
derivative of mandelic acid nitrile in a twophase wa
ter—organic medium using anionic CoIII complexes 1—3
as phase transfer catalysts for transferring PhCHO into
the aqueous phase. Complexes 1—3 are readily soluble in
water and are mainly accumulated in the aqueous phase
when placed in a toluene—water system.