Cp2Ti(III)Cl and Analogues as Sustainable Templates in Organic Synthesis

Abstract

This short review aims to provide an overview of the use of Cp2Ti(III)Cl and other related titanocene(III) species as coordinating reagents­ in template reactions in the selective preparation of C–C and C–O bonds. These complexes are able to assemble two components to produce powerful reactions possessing high regio-, chemo-, diastereo-, and enantioselectivity. The titanocene templates are divided into five structural types. The chemical transformations by these valuable templates, the substrate scope and mechanistic insights will also be described.1 Introduction2 Precedents for the Coordination of Ti(III) Species to Heteroatoms2.1 Coordination of Compounds with Hydrogen–Heteroatom Bonds to Ti(III) Species2.2 Coordination of Halogens to Ti(III) Species3 Types of Titanocene Templates4 Template Type I Mediated Organic Reactions4.1 Methylenecyclopropanation of Allylic Alcohols4.2 Base-Free O-Acylation of Alcohols and Phenol4.3 Epoxidation of Allylic Alcohols5 Template Type II Mediated Organic Reactions5.1 Ketone–Nitrile Cross-Coupling Reactions5.2 Imine–Nitrile Cross-Coupling Reactions5.3 Reductive Alkylation of Enones with Activated Alkenes6 Template Type III Mediated Organic Reactions6.1 Pinacol Coupling of Ketones7 Template Type IV Mediated Organic Reactions7.1 Michael-Type Addition of Aldehydes to Conjugated Enals7.2 Allylation, Crotylation, and Prenylation7.3 Barbier-Type Progargylation and Allenylation8 Template Type V Mediated Organic Reactions8.1 Protection of Alcohols as 2-O-THF and 2-O-THP Ethers8.2 Pinacol Coupling of Aldehydes8.3 McMurry Couplings9 Conclusions and Perspectives

Cp2TiCl/H2O as a Sustainable System for the Reduction of Organic Functional Groups: Potential Application of Cp2TiCl/D2O to the Analysis of Bioactive Phenols in Olive Oil

“…The presence of a vacant site and an unpaired d-electron in the inner sphere of this complex allows its coordination to functional groups with heteroatoms with free valence electrons, obtaining different intermediates if the process is energetically favorable. From these intermediates, important chemical synthesis reactions take place, such as C-C and C-O bond-forming reactions, as well as reduction, isomerization, deoxygenation, protection, epoxidation, and decyanation reactions (Scheme 1) [5][6][7][8][9][10][11].…”

“…In this context, this manuscript summarizes the use of Cp 2 TiCl/water as a green system for the reduction of organic functional groups and its analog Cp 2 TiCl/D 2 O as an efficient system for the synthesis of deuterated compounds, although it is not intended to be a comprehensive review. This system is constituted by Cp 2 TiCl, a single-electron transfer (SET) reagent, which has been proposed as a new green reagent that can carry out an important variety of chemical reactions such as C-C and C-O bond-forming reactions, as well as reduction, isomerization, deoxygenation, and polymerization reactions, under mild reaction conditions and with high diastereo-and regioselectivities [5][6][7][8][9][10][11]. This SET reagent fulfills some of the twelve principles of green chemistry, such as catalysis, safer solvents, waste minimization, atom economy, toxicity, and energy efficiency [5,6].…”

Unprecedented TPE-Embedded Butterfly Bis-Crown Ether with Controllable Conformation and Supramolecular Chiroptical Property

“…Based on the aforementioned experimental data and analyses, it is evident that the yields of these two conformers are influenced by the McMurry reaction condition. [25][26][27][28] The varying amount of zinc powder may induce a templated effect, leading to a preference for one conformer in the product. Additionally, the polar surface of lowvalent titanium would serve as an additional template, simultaneously promoting the formation of one stable conformer structure.…”

A Biomimetic Approach to Premyrsinane-Type Diterpenoids: Exploring Microbial Transformation to Enhance Their Chemical Diversity

“…Cp 2 Ti III Cl has emerged as a useful reagent in organic chemistry because of its versatility to generate single-electron-transfer reactions [ 23 , 24 , 25 , 26 , 27 ]. This complex is easily prepared from commercially available Cp 2 Ti IV Cl 2 by reduction with metals such as Zn [ 28 ] or Mn [ 29 ].…”