Abstract
Isoquinoline 2-oxide (I) reacts with cyanogen bromide in ethanol to give ethyl N-(1- and 4-isoquinolyl) carbamates (II and III) accompanied with some by-products (IV, V, or V' and VI). The amount of II is always larger than that of III and the best yield (42.6%) of II is obtained from the reaction at room temperature for 5 days. 1-Chloroisoquinoline 2-oxide (VII) gives no carbamate and 4-bromoisoquinoline 2-oxides (VIII) afforded 2-isoquinolylcarbamate (IX) in a small yield. While 1-hydroxyisoquinoline 2-oxide (XI) gives only the 4-bromo derivative (XII) by the usual procedure, 4-ethoxycarbonylamino-isocarbostyril (XIII) is produced in 22% yield when sodium acetate is added to the reactants. Although pyridine 1-oxides generally resist this reaction, only 4-hydroxypyridine 1-oxide is highly reactive and ethyl N-(4-hydroxy-3-pyridyl) carbamate hydrobromide (XVIII·HBr) is obtained in 57 % yield. Reactions of 1-aminoisoquinoline 2-oxide (XIV) and 2-aminopyridine 1-oxide (XX) are quite similar to that of 2-aminoquinoline 1-oxide, and the corresponding oxadiazolo derivatives (XV and XXI) are produced without the participation of ethanol.
