1-Oxo-2-cyclohexenyl-2-carbonitrile.
A
dry, 100-mL, round-bottomed flask containing a
magnetic
stirring bar is fitted with an
inlet adapter for
ozonolysis (Note
1, Figure 1) and charged
with
1-cyclopenteneacetonitrile (5.0
g, 46.7 mmol, Note 2)
and
60 mL of dry dichloromethane
(Note
3). A gentle stream of
dry ozone
is passed through the solution and the flask is immediately cooled to −78°C
(Note
4). Ozonolysis is continued until the distinctive blue
color of excess
ozone is
first observed, ozonolysis is then terminated, and the excess ozone is removed by
purging with a stream of
nitrogen
for 5-10 min. The solution is allowed to warm to room temperature, the ozonolysis
adapter
is replaced with a
rubber septum, and
neat
dimethyl sulfide (3.9 g, 62.1 mmol,
Note 5) is added via syringe. The
solution is allowed to stir at room temperature for 36 hr during which time the solution
changes in color from a pale yellow to dark red. The resulting solution is concentrated
under reduced pressure using a
rotary evaporator, and the resulting
thick, red syrup is diluted with
40 mL of
ethyl acetate and washed with water (3 × 25 mL, Note
6). The aqueous phase is extracted with
ethyl acetate (3 × 25 mL),
the organic phases are combined, rinsed with
brine
in order to remove all DMSO, dried (MgSO
4), filtered, and concentrated.
The residual red oil (
5.55 g,
98%) contains only trace impurities
and can be used without purification in most cases (Note
7).
If required, further purification is achieved by rapid radial chromatography (Note
8) on a 2-mm plate using the solvent delivery tip designed for a
4-mm plate and eluting with
50% ethyl
acetate-hexane (Note
9).
The desired fractions are combined and concentrated to provide
1-oxo-2-cyclohexenyl-2-carbonitrile
(
4.8 g,
85% yield) as a pink oil (Note
10).