An efficient synthetic approach for the transition metal-free preparation of 2-bromo-3-(bromomethyl)naphthalene from naphthalene

Abstract

Herein, a new efficient method for the synthesis of 2-bromo-3-(bromomethyl)naphthalene is reported. The synthesis is based on (1) preparation of 1,4-dihydronaphthalene via Birch reduction with mild conditions from the reaction of naphthalene, and (2) the reaction between 1,4-dihydronaphthalene and dichlorocarbene formed in situ from chloroform and potassium tert-butoxide (t-BuOK), and (3) access to the key intermediate 1H-cyclopropa[b]naphthalene from the reaction of 1,1-dichloro-1a,2,7,7a-tetrahydro-1H-cyclopropa[b]naphthalene with t-BuOK, followed by ring-opening of the cyclopropane via bromination with molecular bromine (Br2). This synthetic sequence allows simple preparation of 2-bromo-3-(bromomethyl)naphthalene in higher yields compared to the two previously reported syntheses. The synthetic approach is modular, low cost, and rapid, and can be utilized to synthesize building blocks of naphthalene derivatives.