Organic Syntheses, CV 5, 431
Submitted by K. Hafner, K. H. Vöpel, G. Ploss, and C. König
1.
Checked by S. S. Olin and Ronald Breslow.
1. Procedure
A.
N,N-Dimethylformamide-dimethyl sulfate complex. In a
500-ml. four-necked flask equipped with
mechanical stirrer,
reflux condenser with
calcium chloride drying tube,
dropping funnel, and
thermometer is placed
73 g. (1.0 mole) of dimethylformamide, and
126 g. (1.0 mole) of dimethyl sulfate is added dropwise with stirring at 50–60° (Note
1). After the addition is complete, the mixture is heated for another 2 hours at 70–80°. The dimethylformamide complex forms as a viscous, colorless or pale yellow ether-insoluble oil.
B.
6-(Dimethylamino)fulvene. A
1-l. four-necked flask is equipped with mechanical stirrer, dropping funnel with calcium chloride drying tube, thermometer, and
nitrogen delivery apparatus (Note
2). The flask is flushed with dry
nitrogen, and in it is placed
1.0 mole of cyclopentadienylsodium2 in
700 ml. of tetrahydrofuran (Note
3). The
dimethylformamide-dimethyl sulfate complex prepared above is transferred to the dropping funnel and added slowly with stirring under
nitrogen to the
cyclopentadienylsodium at −10° (
ice-salt bath). During the addition the temperature is kept below −5°. After the addition is complete, the mixture is stirred at 20° for 2 hours. The solution is filtered (with suction) from the precipitated
sodium methyl sulfate, which is washed with another
200 ml. of tetrahydrofuran, and the combined
tetrahydrofuran solutions are concentrated under reduced pressure. The residue is a dark brown oil which solidifies on cooling.
The crude product is crystallized after treatment with activated
carbon from
ca. 1.5 l. of petroleum ether (b.p.
60–80°) or
800 ml. of cyclohexane. From the orange-yellow solution
84 g. (
69%) of
6-(dimethylamino)fulvene separates in yellow leaflets, m.p.
67–68° (Note
4). Concentration of the filtrate and further recrystallization of the residue from
petroleum ether or
cyclohexane gives an additional
8 g. of product. The combined yield is
92 g. (
76%).
2. Notes
2. The nitrogen delivery apparatus has been completely described.
2
3. Air and moisture must be carefully excluded from the reactants during the course of this preparation.
3. Discussion
4. Merits of the Preparation
This procedure illustrates formylation by
N,N-dimethylaminomethoxymethylium methyl sulfate, a compound which can be produced readily by reaction of easily available materials.
6-(Dimethylamino)fulvene is a useful intermediate for the synthesis of various fused-ring nonbenzenoid aromatic compounds.
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