2,4,6-Tris[(4-dichloroiodo)phenoxy)]-1,3,5-triazine as a New Recyclable Hypervalent Iodine(III) Reagent for Chlorination and Oxidation Reactions

Abstract

The synthesis of 2,4,6-tris[(4-dichloroiodo)phenoxy)]-1,3,5-triazine, as a new recyclable nonpolymeric analogue of (dichloroiodo)benzene, is achieved in two steps using 2,4,6-trichloro-1,3,5-triazine and 4-iodophenol. The application of 2,4,6-tris[(4-dichloroiodo)phenoxy)]-1,3,5-triazine for the chlorination reaction of various activated arenes, olefin, and 1,3-diketone is demonstrated. The reagent 2,4,6-tris[(4-dichloroiodo)phenoxy)]-1,3,5-triazine can be applied also for the oxidative synthesis of 1,3,4-oxadiazoles and 1,2,4-thiadiazoles under mild conditions in excellent yields. The recyclability of the 2,4,6-tris[(4-dichloroiodo)phenoxy)]-1,3,5-triazine was possible owing to the facile recovery and reuse of the coproduced 2,4,6-tris(4-iodophenoxy)-1,3,5-triazine from the reaction mixture due to its practical insolubility in methanol.The hypervalent iodine reagents are commercially available, mild, highly selective, and are similar in reactivity to heavy-metal oxidants such as mercury(II), thallium(III), and lead(IV) with fewer toxicity issues. 1 Currently, both iodine(III) and iodine(V) reagents are widely employed in a plethora of oxidative transformations. 2 Dichloroiodoarenes are one of the oldest hypervalent iodine(III) reagents which have been employed as reagents for chlorination and oxidation of various organic substrates, including industrial applications. 3 Dichloroiodoarenes have practical advantage over gaseous elemental chlorine, due to their safe handling and operational simplicity. However, such hypervalent iodine reagents do not have good 'green' credentials because they are commonly used as stoichiometric oxidants and iodoarenes are produced as byproducts. 4 This demands extensive chromatographic purifications to recover and reuse the relatively expensive iodoarenes from the reaction mixture and a quantitative recovery of the iodoarene is seldom achieved. To circumvent this particular problem of atom economy, two strategies have emerged in the last decade of hypervalent iodine chemistry studies: (a) the utilization of several types of recyclable hypervalent iodine reagents including dichloroiodoarenes to facilitate the separation of the iodine coproduct from the reaction mixture as well as the reuse of the reagents (Figure 1) 5-8 and (b) in situ generation of hypervalent iodine using a catalytic quantity of iodoarene in combination with a terminal oxidant (MCPBA, Oxone, or peracetic acid). 9 Regarding dichloroiodoarenes, attempts have been made to recycle the coproduced iodoarene using a polymer-supported reagents strategy 10 as well as fluorous techniques 11 (Figure 1, reagents 1 and 2). 4,4′-Bis(dichloroiodo)biphenyl (3) has been also reported as a recyclable reagent for the halomethoxylation reaction due to the insolubility of 4,4′-diiodobiphenyl in hexane. 12 3-(Dichloroiodo) benzoic acid (4) is the most noteworthy recyclable reagent due to the facile recovery of 3-iodobenzoic acid from the reaction mixture using aqueous NaHCO 3 followed by its precipitation using HNO 3 . 12 Kita and co-wo...

Iodine(III)‐Aluminum or ‐Ammonium Salts for the Oxidative Aromatic Inorganic Functionalization

“…In our procedure, a broad scope not only in the aromatic ring was explored, but also the groups bonded to the oxygen were included. Thus, we found that acetyl, benzyl, pivaloyl or even propargyl groups were tolerated (33)(34)(35)(36), nevertheless, the chemical yields decreased from 93 % to 62-75 %, presumably due to their steric hindrance. Additionally, the methyl or formyl groups (39,40) in the phenolic ring as well as benzimidazolones (41), carbazole (42) and even pharmacologically active drugs such as naproxen (43) or paracetamol (44) were brominated in good to excellent yields.…”

Oxidative Coupling with S–N Bond Formation

“…A number of oxidative systems have been used for this purpose. They include o ‐iodoxybenzoic acid (IBX), 2,4,6‐tris[(4‐dichloro‐iodo)phenoxy]‐1,3,5‐triazine, the I 2 /O 2 /H 2 SO 4 system, CAN, Oxone, NBS, DDQ, t BuONO, pentylpyridinium tribromide, and air oxygen in the presence of organocatalyst (Table ). Unfortunately, this strategy is suitable only for the synthesis of 1,2,4‐thiadiazoles with the same alkyl or aryl substituents at the 3‐ and 5‐positions and without any functional groups in the thiadiazole ring.…”

Preparation, structure, and oxidative reactivity of (dichloroiodo)pyridines: recyclable hypervalent iodine reagents

“…Compared to the reactions of (dichloroiodo)benzene 1 or analogous (dichloroiodo)arenes under similar conditions, the (dichloroiodo)pyridine reagents showed better reactivity and higher yields. [32][33][34] Among the chlorination reactions, the reactions of 4-(dichloroiodo)pyridine 13 gave the lowest yields because of the low solubility of this reagent in methylene chloride. Finally, we have demonstrated that 2-(dichloroiodo)-3-propoxypyridine 9 can be used as a recyclable reagent.…”