- Highly enantioselective iridium-catalyzed hydrogenation of α,β-unsaturated esters
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α,β-Unsaturated esters have been employed as substrates in iridium-catalyzed asymmetric hydrogenation. Full conversions and good to excellent enantioselectivities (up to 99 % ee) were obtained for a broad range of substrates with both aromatic- and aliphatic substituents on the prochiral carbon. The hydrogenated products are highly useful as building blocks in the synthesis of a variety of natural products and pharmaceuticals. Asymmetric hydrogenation: A variety of α,β-unsaturated esters were hydrogenated with high enantioselectivities (see scheme). The hydrogenated products have been used in synthetic transformations as well as in formal total syntheses. Copyright
- Li, Jia-Qi,Quan, Xu,Andersson, Pher G.
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p. 10609 - 10616
(2012/11/07)
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- Enantioselective synthesis of 2-substituted 6- and 7-membered lactones via α-alkylation of lactone hydrazones
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2-Alkyl-substituted lactones 4 were synthesized in good overall yields and high enantiomeric purities (ee = 90-94%) by deprotonation and alkylation of the corresponding lactone SAMP-hydrazones 2 and subsequent oxidative cleavage of the product hydrazones 3 by ozonolysis. The lactone hydrazones 2, in turn, were prepared in good yields by silver promoted cyclization of ω-chloroalkanohydrazides 1.
- Enders,Grobner,Runsink
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p. 947 - 951
(2007/10/02)
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- Asymmetric Synthesis of 2-Substituted Butyrolactones and Valerolactones
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The use of chiral oxazolines 1, 2, 5, and 8 under asymmetrically induced alkylation conditions gave α-substituted oxazolines 3, 6, 9, and 13 which were hydrolyzed to α-substituted butyro- and valerolactones 4 and 11.Either enantiomer of the lactones could be prepared in predictable absolute configuration by reversing the order of alkyl group introduction.The lactones were prepared in 60-86 percent enantiomeric excess which was determined by either chemical correlation or high-pressure liquid chromatography of the diastereomers 10.
- Meyers, A. I.,Yamamoto, Yukio,Mihelich, Edward D.,Bell, Richard A.
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p. 2792 - 2796
(2007/10/02)
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