1984
K. Tanji, J. Koshio, and O. Sugimoto
Scheme 1.
The precipitate was filtered and dried under reduced pressure at 358C to
afford 1.
A microwave oven (Matsushita NE-J720, Japan), with selectable output
power (100 W, 150 W, 300 W, 600 W, 700 W, and 1000 W), was used to
avoid overshooting the reaction.
At first, microwave-assisted dehydration of benzamide derivatives
(benzamide and p-methoxybenzamide) using 1 was carried out (Table 1).
The reaction was terminated when the mixture melted and turned black.
Reaction of benzamide and p-methoxybenzamide with a stoichiometric
amount of 1 at 300 W gave the corresponding nitriles in 24% and 23%
yields, respectively (Table 1, entries 1 and 2). As the amount of 1 was
increased, yields of the products were improved (Table 1, entries 3–5). By
using microwave irradiation, shortening the reaction time became feasible.
At least 4 equivalents of 1 were required to afford the products in good
yields, whereas the use of 1–2 equivalents of 1 were sufficient in the same
reaction in solvents (dioxane or THF) under reflux.[3]
Chlorination of hydroxyheteroaromatics using
1 by microwave
irradiation was examined. 2(1H)-Quinolinone was used to optimize the con-
ditions (amount of 1, irradiating power, and reaction time). A mixture of
2(1H)-quinolinone (2 mmol) and a stoichiometric amount of 1 (2 mmol) was
treated with microwave irradiation until the mixture melted and turned
black under various power outputs (150–1000 W), but similar yields (11–
21%) were obtained (Table 2, entries 1–5). As the amount of 1 was
increased, the yield of the product, 2-chloroquinoline, was improved
(Table 2, entries 6–8).
Next, chlorination of some hydroxyheteroaromatics shown in Table 3 was
examined. Microwave-assisted (300W) halogenation of substrates [4-hydroxy-
2(1H)-quinolinone, 1-phenyl-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one, 2(1H)-
quinoxalinone, 2,3(1H,4H)-quinoxalinedione, 4(3H)-quinazolinone, and
4-phenyl-2(1H)-quinazolinone] with 1 (4 eq.) was carried out to give the
corresponding chloroheteroaromatics in variable yields (0–64%). Because