A re-examination of the Friedel–Crafts acetylation of 2-methoxynaphthalene

Abstract

Acetylation of 2-methoxynaphthalene (I) in carbon disulphide, chloroform, or nitrobenzene, gives various yields of 1-acetyl-2-methoxynaphthalene (II), of 2-acetyl-6-methoxynaphthalene (III), of 1-acetyl-7-methoxy-naphthalene (IV), and small amounts of the corresponding phenols. A 44% yield of compound (II) is obtainable in carbon disulphide, and a 43% yield of compound (III) in nitrobenzene, by different addition procedures. In chloroform, using a Perrier addition, about 7% of 1,6-diacetyl-2-methoxynaphthalene (V) is formed, in spite of much unchanged (I) remaining. Treatment in chloroform of compound (II) under acetylating conditions results in some 3% rearrangement to (III), some 0·3% rearrangement to (IV), and much deacylation to (I); the rearrangement is too slow, however, to account mechanistically for the formation of compounds (III) and (IV) in normal acylations of compound (I). Results from a competitive acetylation show that the 1-position of compound (I) is 1·72 times as reactive, the 6-position 3·8 times as reactive, and the 8-position 0·9 times as reactive as the α-, α-, and β-positions, respectively, of naphthalene.