The Divalent Titanium Complex Ti(O-i-Pr)4/2i-PrMgX as an Efficient and Practical Reagent for Fine Chemical Synthesis

This account describes synthetic transformations of unsaturated hydrocarbons, such as alkynes, alkenes, and dienes, mediated by the divalent titanium reagent Ti(O-i-Pr)4/2 i-PrMgX, which proceed via (ν 2-alkene)- or (ν 2-alkyne)-titanium intermediates. Many of these transformations are otherwise difficult or require multi-step reaction sequences. Since Ti(O-i-Pr)4 and i-PrMgX are non-toxic and available in bulk at low price, the reagent satisfies the qualifications for use in large-scale synthesis. 1 Introduction 2 A General View of the Ti(O-i-Pr)4/2 i-PrMgX Reagent 3 Generation of an (ν 2-Alkyne)Ti(O-i-Pr)2 and its Utilization as a Vicinal Vinylic Dianion 4 Preparation of Allyl- and Allenyltitanium Reagents and their Synthetic Utility 4.1 Allylic Titanium Reagents 4.2 Allenylic Titanium Reagents 5 Intramolecular Nucleophilic Acyl Substitution (INAS) Reactions Mediated by Ti(O-i-Pr)4/2 i-PrMgX 5.1 Scope of the Reaction 5.2 Synthetic Applications of the INAS Reaction 6 Intra- and Intermolecular Coupling of Olefins and Acetylenes 6.1 Intramolecular Reactions 6.2 Intermolecular Reactions 6.3 Tandem Inter- and Intramolecular Reactions 7 Summary and Outlook