One of the most important approaches to the preparation of aldehydes from benzylic alcohols is the use of DMSO-based systems, including DMSO/oxalyl chloride/Et3N (Swern oxidation), DMSO/DCC/Hþ (Pfitzner-Moffatt oxidation), DMSO/P2O5 (Onodera oxidation), DMSO/Ac2O (Albright-Goldman oxidation), 5,6 and DMSO/SO3 Py/Et3N (ParikhDoering oxidation) (Figure 1). Although each of these protocols has its advantages and has been widely adopted, there are also disadvantages, among these the use of toxic and moisture sensitive reagents, the need for low temperatures to avoid Pummerer rearrangement, the requirement of anhydrous conditions, removal of by-products such as urea in the Pfitzner-Moffatt oxidation, and the competitive formation of methylthiomethyl ether. DMSO/I2 is of widening use as an oxidant. 8 Several selective methods for the oxidation of benzyl alcohols to aldehydes have been investigated. Recently, Konwar and coworkers described molecular iodine as an inexpensive and low toxicity reagent, for the oxidation of alcohols. They used iodine in the presence of hydrazine, DMSO, water and MeCN, and also in the presence of KI, K2CO3, and water. 13 They found that the first protocol led to selective oxidation of secondary alcohols. The use of KI and K2CO3 in the second protocol was necessary for the oxidation reaction. Benzyl alcohol was converted to benzaldehyde by the I2/N2H4/DMSO/H2O/MeCN system and the I2/K2CO3/ KI/H2O system with 3.7% and 95% yields, respectively. We now describe a novel DMSO-based approach for the chemoselective oxidation of benzylic alcohols to aromatic aldehydes by molecular iodine. Initially, the reaction conditions were optimized for the oxidation of benzyl alcohol 1a. Different amounts of iodine and several solvents and temperatures were examined. The results are shown in Table 1. The oxidation of benzyl alcohol 1a with DMSO provided only a trace amount of benzaldehyde 2a under reflux conditions even after 7 h (Table 1, entry 1), whereas the production of benzaldehyde reached slightly better yield in the presence of 0.5 equiv. of I2 after 7 h (Table 1, entry 2). The yield of desired product was increased to 35% through increasing of I2 to 1.1 equiv. after 7 h (Table 1, entry 4). To our surprise, the yield was increased when water was added to the reaction mixture (Table 1, entry 5–9) and a better yield was achieved in the DMSO/H2O mixture with a 1:2 ratio (Table 1, entry 8). Then, a diversity of solvents (DCM, acetone, toluene, MeCN, EtOAc, dioxane, BuOH, THF, and DMF) in the optimum ratio (DMSO/solvent [1:2]) were

中文翻译：

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DMSO/水/I2 将苯甲醇氧化为芳香醛：化学选择性氧化

从苯甲醇制备醛的最重要方法之一是使用基于 DMSO 的系统，包括 DMSO/草酰氯/Et3N（Swern 氧化）、DMSO/DCC/Hþ（Pfitzner-Moffatt 氧化）、DMSO/P2O5 （Onodera 氧化）、DMSO/Ac2O（Albright-Goldman 氧化）、5,6 和 DMSO/SO3 Py/Et3N（ParikhDoering 氧化）（图 1）。尽管这些协议中的每一个都有其优点并已被广泛采用，但也有缺点，其中包括使用有毒和湿敏试剂、需要低温以避免普默雷重排、需要无水条件、去除副产物尿素在 Pfitzner-Moffatt 氧化中的产物，以及甲硫基甲基醚的竞争形成。DMSO/I2 作为氧化剂的用途越来越广。8 已经研究了几种将苯甲醇氧化成醛的选择性方法。最近，Konwar 及其同事将分子碘描述为一种廉价且低毒的试剂，用于醇的氧化。他们在肼、DMSO、水和 MeCN 存在下以及在 KI、K2CO3 和水存在下使用碘。13 他们发现第一个方案导致了仲醇的选择性氧化。在第二个协议中使用 KI 和 K2CO3 是氧化反应所必需的。苯甲醇通过 I2/N2H4/DMSO/H2O/MeCN 系统和 I2/K2CO3/KI/H2O 系统分别转化为苯甲醛，产率分别为 3.7% 和 95%。我们现在描述了一种新的基于 DMSO 的方法，用于通过分子碘将苄醇化学选择性氧化为芳香醛。原来，优化了氧化苯甲醇1a的反应条件。检查了不同量的碘和几种溶剂和温度。结果如表 1 所示。 在回流条件下，即使在 7 小时后，用 DMSO 氧化苯甲醇 1a 也仅提供痕量的苯甲醛 2a（表 1，条目 1），而苯甲醛的产量在存在 0.5 当量 7 小时后的 I2（表 1，条目 2）。通过将 I2 增加到 1.1 当量，所需产物的产率增加到 35%。7 小时后（表 1，条目 4）。令我们惊讶的是，当向反应混合物中加入水时，产率增加了（表 1，条目 5-9），并且在比例为 1:2 的 DMSO/H2O 混合物中获得了更好的产率（表 1，条目 8） . 然后，多种溶剂（DCM、丙酮、甲苯、MeCN、