Reactivity and Diastereoselectivity in the Thermal and Lewis Acid-Catalyzed Diels−Alder Reactions of N-Sulfinylphosphoramidates1
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Abstract:
The [4 + 2] cycloaddition reactions of N-sulfinylphosphoramidates, prepared from the corresponding phosphoramidates by treatment with N-(chlorosulfinyl)imidazole, and 1,3-cyclohexadiene were found to be diastereoselective in the absence (>90:10) and presence (>95:5) of Lewis acid. The sulfur configuration of the major adduct from the cycloaddition reaction has been established unambiguously by X-ray crystallography. The use of Lewis acids improved the diastereoselectivity and yield, as well as shortened reaction times. Based on the intermediacy of a tin chelate, and the absence of phosphoryl secondary orbital interactions, a mechanism for the cycloaddition reactions is discussed.Keywords:
Reactivity
Lewis acid catalysis
Imidazole
The progress of development in chiral Lewis acid catalyzed reaction in water is described. Lewis acid surfactant-combined catalyst and chiral bipyridine ligand complex realized catalytic asymmetric hydroxymethylation and ring-opening reaction in water successfully. Furthermore, silica-supported Lewis acid catalyst was applied for asymmetric hydroxylation in water. Keywords: Aldol reaction, Chiral Lewis acid, Epoxide, Green chemistry, Lewis acid, Mannich reaction, Water, asymmetric, organic, solvents
Aldol reaction
Chiral Lewis acid
Lewis acid catalysis
Hydroxylation
Mannich reaction
Acid catalysis
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Lewis acid catalyzed addition of active methylene compounds to mucochloric acid (1) and mucobromic acid (2) affording Knoevenagel aldol adducts, gamma-substituted gamma-butenolides, has been explored. Catalytic efficiencies of various Lewis acids have been compared. Indium acetate (0.25-5 mol %) was found to be the most efficient catalyst.
Methylene
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Sc(OTf)3 is a new type of a Lewis acid that is different from typical Lewis acids such as AlCl3, BF3, SnCl4, etc. While most Lewis acids are decomposed or deactivated in the presence of water, Sc(OTf)3 is stable and works as a Lewis acid in water solutions. Many nitrogen-containing compounds such as imines and hydrazones are also successfully activated by using a small amount of Sc(OTf)3 in both organic and aqueous solvents. In addition, Sc(OTf)3 can be recovered after reactions are completed and can be reused. While lanthanide triflates [Ln(OTf)3] have similar properties, the catalytic activity of Sc(OTf)3 is higher than that of Ln(OTf)3 in several cases.
Trifluoromethanesulfonate
Scandium
Lewis acid catalysis
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Lewis acid catalysis
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Abstract Abstract The analysis of reactivity indices suggests the polar nature of the [2+3] cycloaddition of a-phenylnitroethene to (Z)-C,N-diphenylnitrone. Similar conclusions can be drawn from the investigation of the reaction pathways using the B3LYP/6-31g(d) algorithm. This shows that the cycloaddition mechanism depends on the polarity of the reaction medium. A one-step mechanism is followed in the gas phase and toluene in all the theoretically possible pathways. In more polar media (nitromethane, water), a zwitterionic, two-step rather than a one-step mechanism occurs in the pathway leading to 3,4-trans-2,3,5-triphenyl-4-nitroisoxazolidine. Graphical abstract
Polarity (international relations)
Reactivity
Activation barrier
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Aldol reaction
Lewis acid catalysis
Aldol condensation
Anhydrous
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This chapter highlights the water-compatible chiral Lewis acid catalysts that emphasize their usefulness and potential application in next-generation organic synthesis and may result in the development of novel modes of chemical transformations. Lewis acid catalysis has received much attention in organic synthesis as it often affords access to rate enhancement and chiral induction under mild conditions. The development of asymmetric Mukaiyama aldol reactions in aqueous environments epitomizes the history of the development of water-compatible chiral Lewis acid catalysts. The aldol reaction based on the use of preformed metal enolates provides one of the most fundamental and reliable methods for stereoselective CC bond formation in organic chemistry. To control the absolute configuration of the desired product in Diels-Alder reactions, enantioselective Lewis acid catalysis has been studied extensively through a chiral Lewis acid-dienophile (OC) coordination. It serves as the activation process and defines the structure and concentration of a chiral Lewis acid-dienophile complex in equilibrium.
Aldol reaction
Lewis acid catalysis
Chiral Lewis acid
Hydrogen bond catalysis
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The catalytic properties of bistriflatedibenzotetramethyltetraazaannulenezirconium(IV), [Zr(tmtaa)(OTf)2] a prototype of a novel class of organometallic Lewis acids capable of promoting aldol condensations and allylation reactions in fair to good yields have been disclosed.
Aldol reaction
Cationic polymerization
Lewis acid catalysis
Homogeneous Catalysis
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In general, Lewis acid catalysts are metal-based compounds that owe their reactivity to a low-lying empty orbital. However, one potential Lewis acid that has received negligible attention as a catalyst is the carbocation. We have demonstrated the potential of the carbocation as a highly powerful Lewis acid catalyst for organic reactions. The stable and easily available triphenylmethyl (trityl) cation was found to be a highly efficient catalyst for the Diels-Alder reaction for a range of substrates. Catalyst loadings as low as 500 ppm, excellent yields, and good endo/exo selectivities were achieved. Furthermore, by changing the electronic properties of the substituents on the tritylium ion, the Lewis acidity of the catalyst could be tuned to control the outcome of the reaction. The ability of this carbocation as a Lewis acid catalyst was also further extended to the Michael reaction.
Carbocation
Lewis acid catalysis
Reactivity
Acid catalysis
Diels–Alder reaction
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Lewis acid catalysis
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