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Synlett 2012(1): 155-156  
DOI: 10.1055/s-0031-1290114
SPOTLIGHT
© Georg Thieme Verlag Stuttgart ˙ New York

Molecular Iodine

Xin Wen*
College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310014, P. R. of China
e-Mail: wenxin0219@163.com;

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Publication History

Publication Date:
13 December 2011 (online)

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Biographical Sketches

Xin Wen was born in 1987 in Shanxi province, P. R. of China. She studied applied chemistry at the Zhejiang University of Technology and obtained her B.S. degree in 2009. Currently, she is a postgraduate student under the supervision of Prof. Weimin Mo and Prof. Guofu Zhang at the same university. Her research interest mainly focuses on metal-free oxidative reactions.

Introduction

Molecular iodine is a bluish-black solid under standard conditions. It is highly soluble in nonpolar organic solvents and only slightly soluble in water owing to its lack of polarity. However, the solubility in water may be substantially increased in the presence of dissolved iodides due to the formation of triiodide ions. Since first discovered by Bernard Courtois in 1811 [¹b] the interest in utilization of molecular iodine in organic chemistry has increased dramatically due to its readily available, convenient, relatively cheap and environmental benign characteristics over the toxic heavy metals or complex regents. Many types of reactions can be promoted by iodine, [¹] [²] such as the oxidation of alcohols, C-C/C-N bond formation and formation of heterocycles, etc.

Abstracts

(A) Instead of the traditional palladium-catalyzed Wacker oxidation, Itoh and co-workers [³] have reported an one-pot synthetic protocol of acetophenones from styrenes with molecular iodine, visible light and oxygen. Regardless of various substituents at the aromatic ring, the corresponding acetophenones could be obtained in moderate to good yields. This procedure involves aerobic photooxidation and deiodination in one pot and provides the first report of metal-free ­direct syntheses of acetophenones from styrenes.

(B) By employing catalytic amount (10 mol%) of I2 and [hydroxy(tosyloxy)iodo]benzene (HTIB, Koser’s reagent), Giannis et al. [4] have described a new and efficient synthetic method for diverse tetrahydrofuran derivatives. Compared to the previous systems such as Pd(II)/DIB [5] or NaIO4/NaHSO3, [6] the present methodology exhibits obvious advantages; it is a one-step, metal-free and simple operation and has also great applicability in the synthesis of biologically active natural products.

(C) Iodine-induced regioselective C-C and C-N bond forming reactions of N-protected indole derivatives were reported by Liang and co-workers. [7] Compared with the transition-metal-catalyzed cross-couplings requiring noble metal catalysts and high loading of metal oxidants, the novel coupling method has shown great potential for both industrial and academic purposes.

(D) Nicholas and co-workers [8] have disclosed an I2-catalyzed aminosulfonating system for a broad range of benzylic and some types of saturated hydrocarbons utilizing imido-iodinanes (PhI = NSO2Ar) as aminosulfonating reagent. It was worth to mention that the reaction was highly regioselective for the tertiary C-H of adamantine with no secondary C-H aminated product detected. While in some previous reported transition-metal-catalyzed systems, [9] the regio­selectivity was relatively poor and the ratio of tertiary to secondary aminated products was 3-15:1.

(E) Mao et al. [¹0] have found that the transition-metal-catalyzed ­Suzuki coupling could also be well performed in air using iodine as effective catalyst. In addition, the newly developed metal-free protocol was also applicable for the coupling of (E)-β-bromostyene with phenylboronic acid, with retention of the double bond geometry.

(F) Benzimidazole is an important chemical entity in pharmaceuticals due to its structural similarity to purine. In order to obtain this useful reagent, Lin et al. [¹¹] have developed an efficient method for the conversion of unprotected and unmodified aldoses into aldo-­benzimidazoles and aldo-naphthimidazoles using iodine as oxidant. A series of mono-, di-, and trialdoses containing carboxyl and acetamido groups were introduced into the reaction given the desired products in high yields. Notably, no cleavage of the glycosidic bond occurred under such mild reaction conditions.

(G) Molecular iodine can also be used for deprotection. Konwar and co-workers [¹²] found that the I2/SDS/water system could transform a broad range of oximes and imines to the corresponding carbonyl compounds with moderate to good yields under neutral conditions. it was found that the catalytic amount of I2 could promote the reaction in the presence of surfactant (SDS), meanwhile, no formation of iodoxime/imidoyl iodide or over-oxidized products (acids) were observed during the reaction.

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