A practical asymmetric synthesis of a wide-spectrum agricultural fungicide, (S)-MA20565 (1), is described. The convergent synthesis was achieved starting from commercially available 3-(trifluoromethyl)aniline (7) in 44% overall yield through five steps and 2-bromobenzaldehyde (9) in 48% overall yield through four steps, respectively. (S)-O-[1-(3-Trifluoromethylphenyl)ethyl]hydroxylamine (2), a key intermediate of 1, was prepared via ruthenium(II)-catalyzed asymmetric transfer hydrogenation of 1-(3-trifluoromethylphenyl)ethanone (6) followed by chlorination using methanesulfonyl chloride and oxyamination using potassium acetohydroxamate with high level of stereocontrol.
A catalytic cycle was effectively performed in highly stereoselective glycosylation of 1-O-acetyl-D-glucose by using active species generated from respective combinations of Lewis acids (SnCl4, GeCl4, SiCl4, GaCl3, InCl3, and HfCl4) and silver perchlorate.
In the presence of a catalytic amount of tin(IV) species generated from tin(IV) chloride and silver perchlorate, 1-O-acetyl-d-glucose stereoselectively reacts with silyl alkoxides to give the corresponding α-glucosides in high yields.
Ethyl 4-formyl-1,3-dimethylpyrazole-5-carboxylate showed coloration upon 366-nm light irradiation in the solid state at room temperature. The red color disappeared either by melting or dissolving into solvents. The initiation of coloration is most likely based on a photochemical intramolecular hydrogen abstraction by the formyl oxygen from the methyl group on C-3. It also exhibited coloration in 2-methyltetrahydrofuran matrix at low temperature.
An efficient catalytic β-glycosylation reaction starting from pentaacylglucopyranose and alkyl silyl ether was performed using an active species generated from MeSiCl3 and AgClO4. 1-O-Acetyl-2,3,4,6-tetra-O-pivaloyl-β-D-glucopyranose stereoselectively reacted with alkyl silyl ethers with the assistance of neighboring effect to give the corresponding β-glucosides in high yields.
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