Refernces
10.1021/ja076797c
The study presents a novel catalytic asymmetric cyclopropanation reaction of enones using dimethyloxosulfonium methylide, promoted by a La-Li3-(biphenyldiolate)3 + NaI complex. The reaction showcases high enantioselectivity, with up to 99% ee, and is applicable to a variety of enones, including those with electron-withdrawing or electron-donating substituents and heteroaryl-substituted enones. The use of NaI as an additive, along with biphenyldiol as a ligand, is crucial for achieving this level of selectivity. The reaction conditions were optimized to allow for slow addition of enones, which further improved the enantioselectivity. The study also explores the potential of the catalyst system with other substrates, such as an N-acylpyrrole, and discusses the role of NaI in the reaction mechanism, suggesting a partial alkali metal exchange occurs in situ to form a La-Li2-Na-(biphenyldiolate)3 complex. The findings provide a complementary approach to existing methods for catalytic asymmetric cyclopropanation and highlight the importance of the mixed-alkali metal system in achieving high yields and enantioselectivity.
10.1016/S0040-4020(01)86584-4
The research investigates the migration of perfluoroalkyl groups in the rearrangement of 4-perfluoroalkyl-4-quinols. Key chemicals involved include 4-(perfluoro-n-alkyl)-4-hydroxy-2,5-cyclohexadien-1-one (4-perfluoroalkyl-4-quinols), which undergo base-catalyzed rearrangement to form products like 2-(perfluoro-n-alkyl)hydroquinone or 5-(perfluoro-n-alkyl)-2-cyclohexen-1,4-dione, depending on the substitution pattern. Other chemicals such as dimethylsulfonium methylide and dimethyloxosulfonium methylide were used in attempted preparations of 4-(perfluorooctyl)benzaldehyde, resulting in various by-products. The study also explored the acyloin rearrangement of different 4-perfluoroalkyl-4-quinols, revealing that the presence of substituents next to the carbonyl group retards migration, while substituents adjacent to the perfluoroalkyl group promote it.
10.2174/157017809790443005
The study presents a new method for preparing N-tosyl-L-phenylalanine chloromethyl ketone (TPCK), an irreversible serine protease inhibitor, without using toxic and explosive diazomethane. L-Phenylalanine is first tosylated to form N-tosyl-L-phenylalanine, which is then converted into its 4-nitrophenyl ester using DCC and DMAP. This ester reacts with dimethylsulfoxonium methylide, generated from trimethylsulfoxonium iodide and potassium tert-butoxide, to form a sulfur ylide. The sulfur ylide is subsequently treated with lithium chloride and methanesulfonic acid to produce the chloroketone, TPCK. This method achieves an overall yield of 36% and avoids the use of hazardous diazomethane, providing a safer and practical synthesis route.
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