Tetrahe.xkon Letters, Vol.32, No.38, pp 5179-5182, 1991
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C O B A L T ( I I ) C H L O R I D E C A T A L Y S E D A C Y L A T I O N OF A N I S O L E
Javed Iqbal
, M.A. Khan and Naresh K. Nayyar
Dept. of Chemistry, Indian Institute of Technology, Kanpur-208016, India
Abstract
:
Cobalt(ll)chloride
variety of acid
to give p-acylated anisoles in good yields.
catalysed
acylation
of
anisole
with
chlorides proceeds via an acyl radical
The acylation of aromatic ring with acid halides in presence
of aluminium trichloride (The Friedel-Crafts reaction) is an extremely
useful organic transformation in the domain of electrophilic aromatic
substitution reactions. These acylations can be promoted by other Lewis
acids, however, the scope of this reaction is severely limited owing
to the requirement of the Lewis acid in stoichiometric amounts.
acylation of activated arenes like anisole may be promoted 2 by Bronsted
acid in moderate yields. In contrast, copper(I) promoted acylation 3
The
of anisole with selenol esters may be achieved in good yields. However,
the use of selenium compounds in these acylations severely limits the
scope of these reactions.
In view of the above limitations,
catalyst during these acylations seemed an attractive alternative
therefore, we now show that cobalt(II)chloride is an efficient
the use
of
a
and
catalyst for the acylation of anisole with various acyl chlorides.
Typically,
acid
chloride
(16 mmol)
and
aromatic
compound
(8 mmol) is added to
a
solution of anhydrous cobalt(II)chloride (5
mol %) in dry acetonitrile (30 ml) and the resulting mixture is heated
at 80°C for 10-15 hours. The acetonitrile is removed under vacuum and
the residue taken into ether (80 ml) and washed successively with satura-
ted solution of sodium bicarbonate and water. Drying (MgSO4) and evapo-
ration of the organic layer yielded
chromatography gave the acylated products
(Schemel).
pounds
a
liquid which on flash column
2
and in good yields
3
These reactions work well with electron rich aromatic com-
The acylation of anisole gave mainly the para
like anisole.
acylated compounds (2a-d) which are accompanied by
( ~ 5 % ) of the corresponding ortho isomers. Benzene, toluene and thio-
anisole do not give good yield of the acylated products under these
conditions. These acylations are always accompanied by 5-10% of the
derived from the corresponding acid chloride. Small amounts
and the coupled product were obtained in all the reactions.
a
very small amount
a
biacyl
of ester
3
4
5179