Nucleophilic Substitution of Diethyl 2‐Chloroazulene‐1,3‐dicarboxylate with Alkyl Lithium

Abstract

Nucleophilic substitution reactions of diethyl 2‐chloroazulene‐1,3‐dicarboxylate with four alkyl lithiums (methyl lithium, ethyl lithium, n‐propyl lithium and n‐butyl lithium) afforded the major product of ethyl 2‐chloro‐4‐alkylazulene‐1‐carboxylate and some minor products of 2‐chloro‐4‐alkylazulene, 2,4‐dialkylazulene‐1‐carboxylic acid, ethyl 3,4‐dialkylazulene‐1‐carboxylate, diethyl 6‐alkylazulene‐1,3‐dicarboxylate and diethyl 2‐chloro‐5‐alkylazulene‐1,3‐dicarboxylate, respectively. The kinds and the yields of their products were significantly dependent on the kinds of alkyl lithiums, molar ratios of alkyl lithium/substrate and oxidation conditions at room temperature or under reflux. The major product of ethyl 2‐chloro‐4‐alkylazulene‐1‐carboxylate is proposed to be formed via an addition‐elimination mechanism.