Organic Syntheses, Coll. Vol. 5, p.263 (1973); Vol. 48, p.55 (1968).
A 2-l. three-necked flask
is thoroughly dried and fitted with a large dry-ice condenser
, a mechanical stirrer
, a nitrogen inlet
, and a powder funnel in an efficient hood
. With nitrogen
flowing through the system, 62.5 g. (1.60 moles) of commercial sodium amide (Note 1)
is added rapidly. (Caution! Sodium amide is corrosive and readily decomposes in the presence of moisture.)
The funnel is replaced by a gas-inlet tube, the condenser is filled with a mixture of dry ice and acetone
, and ca. 400 ml. of liquid ammonia
is introduced from a cylinder. The gas-inlet tube is replaced by an addition funnel, stirring is commenced, and 66.3 g. (0.400 mole) of o-chlorohydrocinnamonitrile (Note 2)
is added over a 10-minute period. The last traces of the nitrile are washed into the flask with small amounts of anhydrous ether
The dark green reaction mixture is stirred vigorously for 3 hours and then is treated carefully with 96 g. (1.2 moles) of solid ammonium nitrate (Note 3)
. All the fittings are removed from the flask, and the ammonia
is allowed to evaporate (Note 4)
. Water (300 ml.) is added cautiously to the residue. (Caution! Traces of undecomposed sodium amide may adhere to the upper walls of the flask.)
The organic layer is taken up in two 160-ml. portions of chloroform
, and the solutions are combined and washed twice with 100 ml. of 5% hydrochloric acid
and once with 100 ml. of water. (Caution! The extraction procedure and subsequent chloroform distillation should be conducted in a hood because some hydrogen cyanide is usually evolved.)
solution is dried over anhydrous sodium sulfate
, and the chloroform
is removed by distillation. The residual liquid is distilled under reduced pressure through an insulated, 5-in. Vigreux column
. The forerun, b.p. 95–100° (3 mm.)
, weighs ca.
1 g.; the product boils at 100–101° (3 mm.)
1.5451. The yield of 1-cyanobenzocyclobutene
is 33–34 g.
) (Note 5)
and (Note 6)
The sodium amide was obtained from Farchan Research Laboratories and was approximately 90%
Overnight evaporation at room temperature is convenient.
The submitters carried out the reaction on 1-molar and 3-molar scales and obtained yields of 62–64%
4. Merits of the Preparation
Cyclization by addition of a side-chain carbanion to an aryne bond has been proposed as the method of choice for synthesis of the versatile 1-substituted benzocyclobutene
This general procedure now has been modified to permit convenient large-scale preparations utilizing a commercially available base, a minimum amount of liquid ammonia
, and distillation for isolation of the product.
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