Showing papers by "Vinod K. Singh published in 2013"

Enantioselective synthesis of 3,4-dihydropyran derivatives via a Michael addition reaction catalysed by chiral pybox-diph-Zn(II) complex.

Abstract: An enantioselective Michael addition of cyclic 1,3-dicarbonyls to 2-enoylpyridine N-oxides catalyzed by a chiral pybox–diph–Zn(II) complex has been developed The corresponding Michael adducts have been obtained in high yields with up to >99% ee The Michael adduct has been transformed to biologically active 2,4-disubstituted hexahydroquinoline A plausible transition-state model has been proposed to explain the stereochemical outcome of the reaction

Enantioselective Mukaiyama–Michael with 2-enoyl pyridine N-oxides catalyzed by PYBOX-DIPH-Zn(II)-complexes at ambient temperature

Abstract: A chiral PYBOX-DIPH-Zn(II) catalyzed enantioselective Mukaiyama–Michael reaction of acyclic silyl enol ethers with 2-enoylpyridine N-oxides has been studied in external additive free conditions at ambient temperature. The methodology offers straightforward access to a variety of functionalized chiral 1,5-dicarbonyl compounds, which could easily be elaborated into synthetically viable pyrones via hydrolysis followed by cyclization. A transition state model has been proposed to explain the stereochemical outcome.

Recent aspects of enantioselective epoxidation reactions

Abstract: The latest accepted mechanisms of Katsuki -sharpless epoxidation, proposed by Sharpless and Corey independently, have been described. The recent developments of chiral porphyrin and salen-based metal complexes and their uses as catalysts for asymmetric epoxidation of unfunctionalized olefins (non-directed epoxidation) have been briefly reviewed.

Benzenecarboperoxoic acid, 1, 1‐dimethylethyl Ester

Abstract: [614-45-9] C11H14O3 (MW 194.23) InChI = 1S/C11H14O3/c1-11(2,3)14-13-10(12)9-7-5-4-6-8-9/h4-8H,1-3H3 InChIKey = GJBRNHKUVLOCEB-UHFFFAOYSA-N Alternate Names: tert-butylperbenzoate; tert-butyl benzoperoxoate; tert-butyl peroxybenzoate; Luperox P; Trigonox C. Physical Data: Slightly yellow colored liquid, Boiling point (range): 75–76 °C 0.2 mmHg; Vapor pressure: 3.36 mmHg 50 °C; Vapor Density 6.7 g/l; Density 1.034 g/cm3; Refractive Index 1.496. Solubility: Soluble in various organic solvents such as ethers, ethyl acetate, chlorinated hydrocarbons, aromatic hydrocarbons. Preparative Method: ethyl chloroformate (0.4 mL, 5 mmol) was added dropwise to a solution of benzoic acid (or substituted benzoic acid) (5 mmol) and triethylamine (0.7 mL, 5 mmol) in CH2Cl2 (15 mL) at 0 °C under N2 atmosphere. After stirring the reaction mixture for 30 min, triethylamine (0.7 mL, 5 mmol) was again added. Then, tert-butyl hydroperoxide (5–6 M in nonane, 1.1 mL, 6 mmol) was added dropwise to the solution while maintaining the reaction temperature at 0 °C. The reaction was warmed to room temperature and then stirred for 12 h. It was diluted with CH2Cl2 and washed with aqueous NaHCO3, water, and brine. The organic layer was dried (anhyd. Na2SO4) and the solvent was evaporated on a rotary evaporator to get a crude yellow liquid, which was purified over silica gel by column chromatography (65–85% yield).1a Caution! Peroxy compounds present a serious detonation hazard. While peresters are not nearly as reactive as peracids, use of a Teflon-coated spatula for solid material is recommended. Purification: after purification by column chromatography using EtOAc and petroleum ether the perester can be obtained as a colorless liquid at room temperature and atmospheric pressure under N2. Handling, Storage, and Precautions: benzenecarboperoxoic acid, 1,1-dimethylethyl ester 1 is slightly yellow color liquid and an oxidizing agent and reacts with electron-rich species easily. Store this reagent at 2–8 °C to prevent decomposition. Consult the MSDS (Material Safety Data Sheet) before using. It is advisable to keep this material away from combustible materials, heat, sparks, and open flames. Use only in a chemical hood, remove and wash contaminated clothing thoroughly after handling this reagent. Contact with combustible material may cause fire. This reagent emits toxic fumes when combusted. Harmful if swallowed. Irritating to eyes, respiratory system, and skin. Store under N2 to prevent decomposition to benzoic acid. The material is pyrophoric (autoignition) in nature. Users are encouraged to wear self-contained breathing apparatus, heavy rubber gloves, and protective clothing to prevent contact with skin and eyes. If swallowed, wash mouth with water provided the individual is conscious. If inhaled, remove person to fresh air. In case of contact with skin and eyes, flush with copious amounts of water for at least 15 min. Assure adequate flushing by separating the eyelids with fingers. Consult a physician.

Enantioselective Mukaiyama—Michael with 2-Enoyl Pyridine N-Oxides Catalyzed by PYBOX-DIPH-Zn(II)-Complexes at Ambient Temperature.

Abstract: A chiral PYBOX-DIPH-Zn(II) catalyzed enantioselective Mukaiyama–Michael reaction of acyclic silyl enol ethers with 2-enoylpyridine N-oxides has been studied in external additive free conditions at ambient temperature. The methodology offers straightforward access to a variety of functionalized chiral 1,5-dicarbonyl compounds, which could easily be elaborated into synthetically viable pyrones via hydrolysis followed by cyclization. A transition state model has been proposed to explain the stereochemical outcome.

Bifunctional chiral urea catalyzed highly enantioselective Michael addition of cyclic 1,3-dicarbonyl compounds to 2-enoylpyridines

Abstract: A highly efficient cinchona alkaloid based bifunctional urea catalyzed enantioselective conjugate addition of cyclic 1,3-dicarbonyl compounds to a range of β-substituted 2-enoylpyridines has been developed. Chiral 2,4-diaryl substituted 1,4-dihydropyridines could easily be accessible from these Michael adducts. Significantly, this asymmetric methodology could afford both enantiomers of the products with the same level of enantioselectivities by using pseudoenantiomeric catalysts with up to 98% ee and in excellent yields.