Modern methods for the sythesis of substituted naphthalenes

Abstract

The importance of naphthalenes and naphthoquinones as bioactive agents and in structural and synthetic chemistry is discussed. How the synthetic chemist gains access to such compounds forms the subject of this review. The synthesis of polysubstituted naphthalenes is often not simple by conventional electrophilic aromatic substitution owing to the important problem of regio chemical control. The current general de novo approaches to naphthalenes attempt to circumvent this problem, and include rearrangements and condensations in which the substitution pattern of the aromatic product is determined by the structure of the starting materials. This review, without attempting to be totally comprehensive, serves to illustrate the applications of these general methods and the variation thereof. The authors have also chosen to illustrate with representative examples mainly those methods that show the conversion of single ring benzene precursors into naphthalenes. Routes in which a pre-existing naphthalene core is modified are specifically excluded. Most of the material in this review covers the period from 1999 to the end of 2001, although common traditional methods for the synthesis of substituted naphthalenes will also be mentioned. Where deemed appropriate, some extensions to polycyclic aromatic compounds will also be included. While there is no general review on the synthesis of naphthalenes and naphthols, there are reviews on some aspects of the material covered in this review, which will be mentioned in the appropriate sections. Some partially related reviews covering benzannulation reactions have also recently been published.