Hypervalent Iodine Reagents in the Synthesis of Heterocyclic Compounds

The two hypervalent iodine reagent systems: (i) iodobenzene diacetate (IBD) in methanolic potassium hydroxide and (ii) [hydroxy(tosyloxy)iodo]benzene (HTIB) in a neutral solvent system in conjugation with an appropriate reagent find extensive use in the synthesis of a wide variety of heterocyclic compounds. The present Account is focussed on our results on this topic of current interest. 1. Introduction 2. Synthesis of Heterocycles Using Iodobenzene Diacetate in Methanolic Potassium Hydroxide 2.1. 2-Aroylcoumaran-3-ones 2.2. Flavonoids 2.2.1. cis- and trans-3-Hydroxyflavanones and 2-Furyl Analogues 2.2.2. C(3)-Hydroxylation of Chromones, Flavones and α-Naphthoflavone 3. HTIB Induced Syntheses of Heterocycles 3.1. Heterocycles and Bridgehead Heterocycles Based on the Analogy of α-Tosyloxy Ketones and α-Halogeno Ketones 3.1.1. 2-Amino Substituted Amino and Related Thiazoles (Modified Hantzsch Thiazole Synthesis) T 3.1.2. Selenazoles 3.1.3. 2-Hydroxy- and 2-Mercaptothiazoles 3.1.4. 2-Mercaptoimidazoles (Modified Marckwald's Synthesis) 3.1.5. 2,4-Diaryloxazoles via α-Aroyloxyacetophenones 3.1.6. Pyrazoles 3.1.7. Benzofurans via α-Aryloxyacetophenones 3.1.8. 2-Aroylcoumaran-3 -ones 3.1.9. Bridgehead Heterocycles 3.2. Some Miscellaneous Examples 3.2.1. Flavanones → Isoflavones 3.2.2. Flavanones → Flavones 3.3. 5-Substituted 2-Aryl-4-methyloxazoles 4. Conclusions 5. References