B.
2-Phenylfuro[3,2-b]pyridine. A
300-ml., three-necked flask fitted with a
nitrogen inlet stopcock, a
magnetic stirring bar, and a
condenser attached to a nitrogen outlet stopcock and a
mercury trap is charged with
2.47 g. (0.0150 mole) of copper(I) phenylacetylide. The system is purged with
nitrogen for 20 minutes before
80 ml. of pyridine (Note
9) is added. The resulting mixture is stirred for 20 minutes under a
nitrogen atmosphere (Note
10), and
3.30 g. (0.0149 mole) of 3-hydroxy-2-iodopyridine (Note
11) is added. The mixture, which changes in color from yellow to dark green as the acetylide dissolves (Note
12), is warmed in an oil bath at 110–120° for 9 hours with continuous stirring under a
nitrogen atmosphere (Note
10). The reaction solution is transferred to a
500-ml., round-bottom flask and concentrated to a volume of 20 ml. at 60–70° (20–80 mm.) with a rotary evaporator. The
pyridine solution is treated with
100 ml. of concentrated aqueous ammonia, and the resulting deep-blue mixture is stirred for 10 minutes and extracted with five
100-ml. portions of ether. The combined ethereal extracts are washed with three 250-ml. portions of water, dried over anhydrous
magnesium sulfate, and concentrated with a rotary evaporator. The crude product,
2.6–2.76 g. of orange semisolid, is dissolved in
100 ml. of boiling cyclohexane. The solution is filtered, concentrated to a volume of about 30 ml., and cooled in an
ice bath. The partially purified product crystallizes as
2.3–2.7 g. of orange solid, m.p.
83–89°. Further purification is effected by sublimation at 110–120° (0.01–0.2 mm.), yielding
2.2–2.4 g. (
75–82%) of a yellow solid, m.p.
90–91° (Note
13).