Recent applications of rare-earth metal(III) triflates in cycloaddition and cyclization reactions

Abstract

Rare-earth metal(III) triflates are extremely mild, efficient and water-tolerable Lewis acid catalysts for a wide range of organic transformations. Rare-earth metal triflates retain activity even in the presence of multiple Lewis bases containing oxygen, nitrogen, sulfur and phosphorus atoms, and can be easily recovered and reused without any loss of catalytic activity. This review summarizes recent developments and highlights key applications of these unique Lewis acids in cycloaddition and cyclization reactions.

Conversion of CO2 into Cyclic Carbonates under Ambient Conditions Catalyzed by Rare-Earth Metal Complexes Bearing Poly(phenolato) Ligand

“…RE-containing compounds have been used as optical, electrical, and magnetic materials. , They have also been developed as catalysts, possessing advantages of good activity and selectivity . Rare-earth metals are highly oxyphilic and Lewis acidic, which makes their complexes potentially useful for the cycloaddition of CO 2 and epoxides. , To date, cyclic carbonate synthesis catalyzed by a RE-based complex still requires high temperature and pressure, which include SmOCl (supercritical CO 2 , 200 °C), Sc­(OTf) 2 (20 bar CO 2 , 120 °C), and polynuclear lanthanide complexes (10–20 bar CO 2 , 120 °C), ,, Our group has been devoted to exploiting the application of RE complexes in CO 2 transformations. ,,,,− We reported a RE complex bearing ethylenediamine-bridged poly­(phenolato) ligands, which is the first RE complex that catalyzed the cycloaddition reaction under mild conditions (85 °C and 1 bar CO 2 for monosubstituted epoxide or 10 bar CO 2 for disubstituted epoxide) . In ligand precursor, i.e., ethylenediamine-bridged tetra­(phenol), the fourth phenol moiety is not necessary for charge balance but makes the coordination environment crowded, which may hinder substrate binding to metal centers.…”

Sc(OTf)3 catalyzed carbon-carbon and carbon-heteroatom bond forming reactions: a review

“…Morikawa et al 32 demonstrated a simple and straightforward cyclocondensation of 1,3-dialkoxybenzenes ( 24) with 1,3,5-trioxane (25) to produce resorcin [4]arene octaalkyl ethers (26) in good yields using catalytic amount of Sc(OTf)3 in acetonitrile at 80 o C (Scheme 8).…”

“…The last decade has seen a great development in the use of triflate salts as catalysts for organic transformations. 4 Among triflate salts, the applications of scandium(III) trifluoromethanesulfonate [Sc(OTf)3, scandium triflate] as a Lewis acid catalyst have increased rapidly in the variety of organic transformations that can be effected. [5][6][7][8][9][10][11][12][13][14][15][16][17] The catalytic applicability of this mild catalyst is well documented in the literature, especially in cycloaddition reactions, 18 Diels-Alder, 19 Ugi, 20 and Michael reactions.…”

Scandium(III)‐Triflate‐Catalyzed Multicomponent Reactions for the Synthesis of Nitrogen Heterocycles

“…Once most of Lewis acids used as catalysts in MCRs are decomposed/deactivated in the presence of water (even as traces in non‐dried solvents), the search for water‐resistant Lewis acid catalysis is mandatory for the development of more efficient MCR methodologies [22] . Rare earth metal triflates [RE(OTf) 3 ], comprising Sc(OTf) 3 , Y(OTf) 3 and Ln(OTf) 3 (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu), are efficient water‐compatible Lewis acids used as catalysts for a wide range of organic transformations, including carbon‐carbon bond formation reactions, cycloadditions and cyclization reactions [23–25] . They were introduced in Organic Synthesis in 1987, when Forsberg et al.…”