General Papers ARKIVOC 2009 (xiii) 200-210
Table 2. Amount of HIO3 on the iodination yield of N-phenylmorpholinea
Entry HIO3 (mmol) Yield (%)b
1 0.4 40 2 0.6 45 3 0.8 67 4 1 80 5 1.2 92 6 1.4 92 a Reaction conditions: KI (1.2 mmol), time: 15 min.; Solvent: CH2Cl2/H2O (1:1); room temperature. b Isolated yields.
With a better understanding of the reaction variables, a series of aromatic amines were subjected to iodination with potassium iodide and iodic acid at room temperature in CH2Cl2/H2O
(1:1) as a two phase system. In all reactions, we observed that mono-iodination took place and regioselective iodination occurred at the more active and less hindered sites (Table 3, Scheme 1). Even though it seems that HIO3/KI is capable of oxidizing alcohol, 34 it remains intact during the iodination of aromatic nucleus (Entry 4). Several attempts to produce mono iodinated derivative of phenol were unsuccessful and led to a sluggish mixture. We have extended our reaction to a series of unactivated aromatic compounds as depicted in Table 3, these compounds were unreacted even after 2 h (Entries 8, 9). KI,HIO3CH2Cl2-H2O(1:1) r.t.,15minNIONO Scheme 1. Iodination of aromatic amines using KI and iodic acid.
To extend application of this method in organic reactions and transformations, we have employed our method as a catalytic system for trimethylsilylation of alcohols and phenols. In this context, we have found that a combination of iodic acid and a catalytic amount of KI in the presence of HMDS generate I2 in situ as an efficient catalyst for the trimethylsilylation of alcohols and phenols (Scheme 2). To find the best system for in situ generation of I2, first we studied a number of oxidizing agents in combination of KI for the trimethylsilylation of alcohols and phenols. As it can be seen in Table 4, the best results are related to the HIO3/KI system.
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