Chemistry Reference
In-Depth Information
OO
OO
R
R
R
(COCl)
2
R
R
Route a) VOF
3
/BF
3
*Et
2
O
Route b) Tl
2
O
3
/BF
3
*Et
2
O
TFA/TFAA
R
R
R
R
R
AlCl
3
/CS
2
1257
1258
1259
R = CH
3
, 44 %, C
6
H
13
, 42%, OCH
3
, 1.7 %, O-i-C
5
H
11
, 45 %
Subsequent intramolecular oxidative coupling with either vanadium(V) oxyfluo-
ride/boron trifluoride diethyl ether etherate or thallium(III) oxide/trifluoracetic
acid resulted in the corresponding phenanthrene-9,10-diones 1259. It has been
shown that oxygen functionalities at the 3-, 3
0
-, 4-, and 4
0
-positions are necessary
for coupling to occur. These substituted benzils and phenanthrene-9,10-diones
constitute precursors for ligands in the field of discotic metallomesogens or poly-
meric mesogens.
General procedure. Alkyl-alkoxy-substituted benzils 1258 [943]. Solvents and glassware
used in this synthesis were thoroughly dried prior to use. To a mechanically stirred
suspension of the alkyl- or alkoxybenzene 1257 (200 mmol) and aluminum chlo-
ride (28.3 g, 220 mmol) in carbon disulfide (500 mL) at 0
C, a solution of oxalyl
chloride (15.2 g, 120 mmol) in carbon disulfide (100 mL) was added over a period
of 4 h under a constant stream of argon. Stirring was continued for a further 18 h.
The resulting brown mixture was then poured onto 500 mL of ice and the yellow
organic phase was separated. The aqueous phase was extracted with dichloro-
methane and the combined organic layers were washed with water, dried (MgSO
4
),
and concentrated in vacuo. The resulting orange residue was chromatographed on
a bed of silica gel using dichloromethane as eluent to remove carboxylic acids and
inorganic residues. The obtained material 1258 was then recrystallized from etha-
nol or acetone. Final purification was achieved by column chromatography (silica
gel) with dichloromethane as eluent.
Benzophenones with oxalyl chloride
The product of intermolecular reaction of 1,3-dimethoxybenzene with oxalyl chlo-
ride,inCS
2
or 1,2-dichloroethane, with AlCl
3
, 2,2
0
,4,4
0
-tetramethoxybenzil (mp
129-130
C), was formerly erroneously identified by Staudinger as 2,2
0
,4,4
0
-tetra-
methoxybenzophenone (mp 135-136
C) 1261 [942, 944].
2,2
0
,4,4
0
-Tetramethoxybenzophenone 1261 was obtained by Van Allan [942] by
mixing oxalyl chloride and 1,3-dimethoxybenzene; the solution became reddish-
yellow and hydrogen chloride was slowly evolved. Heating accelerated this evolu-
tion of gas. In order to determine the nature of this reaction, the components
were heated for a few hours, and the reaction mixture was distilled. The distillate
was recrystallized from ethanol to give a substance having a melting point of 135-
136
C, which, from its elemental analysis, methoxyl determination, and Grignard
analysis, proved to be 2,2
0
,4,4
0
-tetramethoxybenzophenone 1261. Demethylation
