chiral «-alkyl -hydroxy esters or acids with high optical purity were determined. This reaction has been now extended, with good results, to other substrates.
Experimental SectionGeneral Methods.NMR spectra were recorded on a Perkin-Elmer (90 MHz) spectrometer using tetramethylsilane as an internal standard. Optical rotations were taken on a Perkin-Elmer 241 polarimeter using a 1-dm cell.Chiral Lithium Alkoxytrialkylaluminates. LiAl-:-Bu3OR*. This reagent can be prepared in stock quantities in the following manner: 5 g (30 mmol) of methyl phenylglyoxylate. After saponification of the -hydroxy ester la, 5.5 g (25 mmol) of crude acid (2a was obtained. Recrystallization in hexane-ethanol (94/6 by volume) gives 3.24 g (52% yield) of pure chiral -hydroxy acid 2a with 98% ee: [a]20D +19.6°(c 2.1, ethanol); mp 131 °C.
Perfluoroalkylation of electron-rich aromatic compounds with trifluoromethyl bromide, or long-chain perfluoroalkyl iodides, was performed in the presence of sodium dithionite or zinc-sulphur dioxide. This alkylation occurred at the ortho and para positions relative to the amino or hydroxy substituent. Pyrroles were perfluoroalkylated regioselectively at the 2-position. This alkylation was interpreted as a radical aromatic substitution; the formation of the perfluoroalkyl radical can be induced by a single-electron transfer from sulphur dioxide radical anion to the perfluoroalkyl halide.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.