Date of Award
Doctor of Philosophy
The main aim of the work presented here is to develop new, practical, economical, and environmental friendly synthetic protocols for various organic transformations with hypervalent iodine compounds, which have attracted explosive interest among chemistry communities because of their versatility and mildness in inducing many organic transformations. Chapter 1 briefly introduces the history of hypervalent iodine compounds, nomenclature, classification, bonding and reactivity patterns. The preparation and practical applications of typical I(III) and I(V) compounds have also been briefly surveyed. Chapter 2 provides details on hypervalent iodine compounds catalyzed oxidation of benzylic C-H to the corresponding carbonyl compounds with Oxone. The catalytic efficiency is influenced by the rate of in situ generation of catalyst with Oxone and their stability. The effectiveness in situ generated 35', 50' and 51' are almost the same, leading to low to moderate yields of products, while 18 and 47' give moderate to high yields. Compound 48' was founds to be the most active catalyst in this study. A possible mechanism is also proposed. Chapter 3 covers a surprising reaction between IBX or IBA and alkyl halides promoted by quaternary ammonium halides. In the absence of quaternary ammonium halides, no reaction occurred between IBX or IBA and alkyl halides. However, in the presence of quaternary ammonium halides, IBX or IBA and alkyl halides react smoothly to form the corresponding alkyl iodobenzoates. When IBX or IBA is treated with a quaternary ammonium halide, it will decompose to 2-iodobenzoic acid. The presence of a nucleophilic halide ion is essential for such reaction to occur. Replacing halides with non-nucleophilic BF4- halts the reaction. Benzylic halides provides a better yield than aliphatic alkyl halide. Thus, it is believed that there is a fast interaction between the nucleophilic halides and electrophilic iodine in IBX or IBA. A plausible reaction mechanism is proposed. Chapter 4 details our research on the oxidative cleavage of C=C with PIFA/water. In the presence of a small amount of water in acetonitrile at 65-70 oC, [bis(trifluoroacetoxy)iodo]benzene (PIFA, 26) converts styrenes into benzaldehydes in good to high yields. Contrary to literature description that electron-rich styrenes primarily produces phenylacetaldehydes as major products through a 1, 2-phenyl migration, we have found that these styrenes can be converted to benzaldehydes in high yields. It was found that three equiv of 26 and one equiv of water were necessary to achieve high yields. Two pathways were believed responsible for the high yield of benzaldehydes: (1) cleavage of the glycol intermediates; (2) further oxidative cleavage of the 1, 2-phenyl migration product - phenylacetaldehydes. Chapter 5 describes a preliminary investigation on perfluoroalkylation reaction of styrene with [bis(trifluoroacetoxy)iodo]butane (32). p-t-Butylstyrene reacts with 32 in the presence of water produced moderate yields of hydroxyperfluorinated product, 1-(4-tert-butyl-phenyl)-3,3,4,4,5,5,6,6,6-nonafluoro-hexan-1-ol (73), along with 1-(4-tert-butyl- phenyl)-2-iodo-ethanol (72) and 1-(4-tert-butyl-phenyl)-ethane-1,2-diol (74). Electrophilic addition of 32 on the C=C bond, hydration of the intermediate, and reductive elimination were believed to have been involved. Chapter 6 summarizes all of the work carried out in the previous chapters and provides some insight into future studies.
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