Synthetic and Mechanistic Studies with Iodine(III) Reagents

Sammanfattning: This thesis describes the development of metal-free transformations and mechanistic studies on the reactivity of two classes of hypervalent iodine reagents: diaryliodonium salts and vinylbenziodoxolones (VBX). Recently, they have been recognized as valuable synthetic reagents with broad applicability in organic synthesis. Moreover, hypervalent iodine reagents are non-toxic compounds and sustainable alternatives to heavy metals. In Chapter 1, an overview of hypervalent iodine(III) compounds is provided, with emphasis on the reagents that have been used in the thesis. First, the synthesis and general reactivity of diaryliodonium salts is described. Vinylbenziodoxolones are presented as a novel class of iodine(III) compounds that are powerful electrophilic vinylating reagents. Finally, a brief description of density functional theory and computational methods used in this thesis are outlined. The synthesis and applications of azobenzene-derived diaryliodonium salts is the topic of Chapter 2. The novel iodonium reagents were employed in chemoselective arylation reactions with a wide range of C, N, O and S-nucleophiles under mild and metal-free conditions. In Chapter 3, a mild and transition metal-free vinylation of thiols and mercapto heterocycles using vinylbenziodoxolones reagents is presented. The method allows the synthesis of a wide variety of S-vinylated products with complete chemo-, regio- and stereoselectivity. In Chapter 4, the first mechanistic investigation of VBX vinylations is presented. By exploiting the use of NMR analysis, deuterium labelling and DFT calculations, the observed regio- and stereochemical outcome of the vinylations of sulfur and phosphorous nucleophiles with VBX reagents has been rationalized. A transition metal-free, photocatalyzed C-vinylation method using VBX reagents is described in Chapter 5. The reactions proceed under mild conditions and the method tolerates a series of functional groups that lead to straightforward access to corresponding alkenes in good to high yields with high stereoselectivity.