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

Abstract

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

Carbozincation of Substituted 2-Alkynylamines, 1-Alkynylphosphines, 1-Alkynylphosphine Sulfides with Et2Zn in the Presence of Catalytic System of Ti(O-iPr)4 and EtMgBr

“…Unfortunately, our attempts to perform this reaction with hept-2-yn-1-ol, oct-3-yn-1-ol, or (hept-2-yn-1-yloxy) benzene in diethyl ether failed. Probably, coordination of the titanium ethylene complex (which can be represented as an equivalent of divalent Ti(O-iPr) 2 stabilized by ethylene ligand [20]) to the oxygen atom of phosphine oxide, alcohol, or ether group gives a stable unreactive organometallic complex. This complex formation inhibits titanium coordination to the triple carbon-carbon bond and thus prevents the formation of titanacyclopentene.…”

Titanium redox catalysis: insights and applications of an earth-abundant base metal

“…12 Two major modifications of the reaction, by de Meigere 13 and Szymoniak, 14 have been developed allowing for the synthesis of cyclopropylamines from amides and nitriles, respectively (Figure 2a). New ligand systems have also been utilized to promote the enantioselective synthesis of cyclopropanols (although with moderate ee’s).…”

Poly(aryleneethynylene)s

“…(5.20)) [122]. The transformation, initially described by Sato [123], is stoichiometric in both titanium and magnesium, but the reduction is quantitative and completely cis-selective. Polymer 69 was further converted to the trans-PAV under UV radiation.…”