The Application of Low-Valent Titanium Reagents in Organic Synthesis

The number and variety of applications of low-valent titanium reagents has expanded greatly since their initial use in 1973. This review examines the preparation of low-valent titanium reagents and their development as reagents for inter- and intramolccular coupling, reductive elimination and alkylidenation, with reference to aspects of the mechanism and stereoselectivity. 1. Introduction 2. Low-Valent Titanium Reagents 2.1. Preparation 2.2. Mechanism and Stereoselectivity 3. Intermolecular Coupling of Aldehydes and Ketones 3.1. Preparation of Alkenes 3.1.1. Preparation of Strained Ethylenes 3.1.2. Preparation of Aromatic Olefins 3.1.3. Mixed Coupling of Carbonyl Groups 3.1.4. Scope and Limitation of the Coupling Reaction 3.1.5. Selective Coupling of Ketones and Aldehydes 3.1.5.1. Groups with Large Reduction Potentials 3.1.5.2. Groups with Low Reduction Potentials 3.2. Preparation of Glycols 3.2.1. Mixed Coupling of Carbonyl Compounds 4. Intramolecular Couplings of Carbonyl Groups 4.1. Preparation of Cycloalkenes and Cyclic Ketones 4.2. Preparation of Cyclic Diols 5. Reductive Eliminations 5.1. Dcoxygenation of Glycols 5.2. Reductive Eliminations of Other Groups 6. Alkylidenation of Carbonyl Groups 6.1. Methylenations 6.2. Alkylidenations 7. Conclusions and Summary