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Condensation of 2-naphthol and naphthalenediols with o-dichlorobenzene in the presence of aluminum halides.

Chemical & pharmaceutical bulletin (2012-06-13)
Konstantin Yuryevich Koltunov, Aleksey Nikolaevich Chernov, Gubbi Krishnamurthy Surya Prakash, George Andrew Olah
ABSTRACT

It is known that 1-naphthol, as a result of superelectrophilic (dicationic) activation in superacid media, is able to react with such deactivated aromatic compound as o-dichlorobenzene to give 4-(3,4-dichlorophenyl)-1-tetralone (2), which is a highly valuable intermediate in the synthesis of the antidepressant, sertraline (1) and other useful derivatives. However, the analogous reactivity of 2-naphthol and a variety of naphthalenediols towards o-dichlorobenzene has not been investigated thus far, although the corresponding tetralones, bearing dichlorophenyl moiety, could be of great pharmacochemical interest. In present work, we disclose that 1,5-, 1,6-, and 1,7- naphthalenediols (6a-c) react smoothly with o-dichlorobenzene in the presence of an excess of aluminum chloride or aluminum bromide to give the pairs of isomeric 4-(3,4-dichlorophenyl)- and 4-(2,3-dichlorophenyl)- 5-, 6-, and 7-hydroxy-1-tetralones (10a-c and 11a-c) in high overall yields. 2-Naphthol and 2,7-naphthalenediol (6d) exhibited comparatively lower reactivity, which however was sufficient to obtain the corresponding dichlorophenyl-2-tetralones in moderate yields. The mechanism of these reactions involving superelectrophilic dicationic or even tricationic intermediates, is discussed.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
1,2-Dichlorobenzene, anhydrous, 99%
Sigma-Aldrich
2-Naphthol, 99%
Sigma-Aldrich
1,2-Dichlorobenzene, ReagentPlus®, 99%
Supelco
1,2-Dichlorobenzene, PESTANAL®, analytical standard
Sigma-Aldrich
1,2-Dichlorobenzene, suitable for HPLC, 99%
Sigma-Aldrich
2-Naphthol, 98%
Sigma-Aldrich
2-Naphthol, fluorescence indicator, ≥99.0%
Supelco
1,2-Dichlorobenzene solution, certified reference material, 200 μg/mL in methanol
Sigma-Aldrich
2-Naphthol, BioXtra, ≥99.0% (GC)
Sigma-Aldrich
1,2-Dichlorobenzene solution, NMR reference standard, 5% in acetone-d6 (99.9 atom % D), NMR tube size 5 mm × 8 in.