[Molecules: 6] [Related articles/posters: 070 037 098 103 056 ]

Regioselective iodination of 1-aza-, 1-oxa- or 1-thia-benzocyclic compounds with mercury(II) oxide and iodine

Kazuhiko Orito, Mitsuhiro Takeo, Takahiro Hatakeyama and Masao Tokuda

Laboratory of Organic Synthesis, Division of Molecular Chemistry, Graduate School of Engineering, Hokkaido University, Sapporo 060, Japan

Introduction
Iodination of N, O or S atom-substituted benzenes with HgO-I₂ reagents
Iodination of benzocyclic amines with HgO-I₂ reagents
Iodination of benzofurans and benzopyrans with HgO-I₂reagents
Iodination of benzothiophene with HgO-I₂ reagents

Introduction

Many methods for the direct iodination of aromatic compounds require acidic or basic reaction conditions, and liberate strong acid. Even iodination of aromatic amines has been carried out in a similar manner, as seen in the currently used methods, such as I₂-AcOH, I₂-HNO₃, I₂-DMSO, KI-I₂-EDA, I₂-morpholine, I₂-NaHCO₃, I₂-DMF-KOH, I₂-CuCl₂, I₂-F₃CCOOAg, I₂-AgSO₄, I₂-HgCl₂, I₂-Al₂O₃, IF, IF₅, DIDH, ICl, PSVP, BTMA-ICl₂, KICl₂, NaOCl-NaI, PyICl, IPy₂BF₄, and I(collidine)₂PF₆. In contrast, the HgO-I₂ reagent provides the neutral and mild reaction conditions, and an easy work-up.

Reaction pathway

A typical procedure for iodination with HgO-I₂ reagent

A suspension of HgO (0.5-3 equiv.), I₂ (1-3 equiv.) and a 0.2 M CH₂Cl₂ solution of the substrate was stirred at room temp, being monitored by TLC. After removal of precipitates, the filtrate was washed with water, dried and evaporated. The crude product was purified by crystallization or distillation.