Hypervalent iodine oxidation of O-silylated phenol derivatives to azacarbocyclic spirodienones; synthetic approach to the anticancer marine alkaloid, discorhabdin C

Synthesis of spirocyclic scaffolds using hypervalent iodine reagents

Hypervalent iodine reagents have been developed as highly valuable reagents in synthetic organic chemistry during the past few decades. These reagents have been identified as key replacements of various toxic heavy metals in organic synthesis. Various synthetically and biologically important scaffolds have been developed using hypervalent iodine reagents either in stoichiometric or catalytic amounts. In addition, hypervalent iodine reagents have been employed for the synthesis of spirocyclic scaffolds via dearomatization processes. In this review, various approaches for the synthesis of spirocyclic scaffolds using hypervalent iodine reagents are covered including their stereoselective synthesis. Additionally, the applications of these reagents in natural product synthesis are also covered.

The regioselective homocoupling of meta-hydroxypyridines with hypervalent iodine(III)

The C - H homocoupling of meta-hydroxypyridines with phenyliodine(III) diacetate (PIDA) was carried out in dichloromethane at room temperature in the presence of cesium carbonate. The coupling reaction is highly regioselective with respect to the hydroxy group at the pyridine ring. Comparative control experiments with meta-alkoxypyridine suggest that the meta-hydroxy group at the pyridine ring plays a key role during the homocoupling reaction.

Enhanced reactivity of [hydroxy(tosyloxy)iodo]benzene in fluoroalcohol media. Efficient direct synthesis of thienyl(aryl)iodonium salts

In this manuscript, we report clear evidence for the generation of aromatic cation radicals produced by using [hydroxy(tosyloxy)iodo]benzene (HTIB) in fluoroalcohol solvents such as 2,2,2-trifluoroethanol (TFE) and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). The single-electron-transfer (SET) oxidation ability of HTIB to give cation radicals was first established by ESR and UV measurements. The reaction was broadly applied to various thiophenes, and unique thienyliodonium salts were directly synthesized by this method in excellent yields without the production of any harmful byproducts.

[Development of novel synthetic organic reactions: synthesis of antitumor natural products and leading compounds for new pharmaceuticals]

Biologically active natural products with unique, highly complex molecular skeletons have been used as leading compounds for raw materials of new drugs. Due to the limitations of natural supply, highly efficient, large-scale syntheses and molecular design have been sought in drug discovery. For this purpose, we have focused on a synthetic strategy effective in developing novel reactions and reagents and found several useful regio- and stereospecific reactions, contributing to the synthesis of otherwise unattainable target molecules. The application of these reactions for the total synthesis of three types of potent cytotoxic natural products for the first time is described in this paper. The basic concept is first described. Then the total synthesis of anthracyclines, fredericamycin A, and discorhabdins is reported. Novel reactions using hypervalent iodine reagents under environmentally benign conditions are also described. The future prospects for this method are discussed.