- Asymmetric Sulfinylations of N-Methylephedrine-Modified Tri- or Tetraalkyl Zincates by Symmetric Diaryl Sulfoxides
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Diethylzinc was treated with 1 or 2 equiv. of AlkMgCl or PhMgBr (preferably) or with 1 equiv. of nBuLi (less efficiently) for forming species – plausibly zincates – which were sulfinylated by diaryl sulfoxides to give racemic alkyl aryl sulfoxides in yields reaching 100 %. Dialkylzinc reagents were also activated by treatments with 1 or 2 equiv. of an enantiomerically pure alkylmagnesium β-aminoalkoxide. This worked best when the alkoxide stemmed from a dialkylmagnesium reagent and an equimolar amount of N-methyl-(–)-ephedrine. This second activation mode allowed sulfinylations of what was originally the dialkylzinc reagent with diaryl sulfoxides. This generated alkyl aryl sulfoxides with enantiomeric ratios up to 93:7 in up to 100 % yield.
- Ruppenthal, Simon,Brückner, Reinhard
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supporting information
p. 2518 - 2530
(2018/06/11)
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- A high-throughput screening protocol for fast evaluation of enantioselective catalysts
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A new high-throughput screening protocol that allows fast evaluation of enantioselective catalysts has been developed. The usefulness of norephedrine-derived β-amino alcohols as catalysts for the enantioselective alkylation of prochiral aldehydes has been determined by simultaneous screening of three representative substrates. GC analysis of the crude product mixture using a selectively modified cyclodextrin as the chiral stationary phase avoids timeconsuming workup procedures. The chemical yield, enantioselectivity, substrate specificity, and catalytic activity of the chiral catalysts as well as the induced absolute configuration have been determined in a single screening experiment and two short GC runs.
- Wolf, Christian,Hawes, Pili A.
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p. 2727 - 2729
(2007/10/03)
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- Enantioselective Addition of Diethylzinc to α-Branched Aldehydes
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Reaction of diethylzinc with α-branched aldehydes in the presence of a catalytic amount of (1R,2S)-(-)-1-phenyl-2-piperidinopropane-1-thiol 1 provided the corresponding secondary alcohols in almost 100percent enantiomeric excess.
- Kang, Jahyo,Lee, Jun Won,Kim, Joo In
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p. 2009 - 2010
(2007/10/02)
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- Chiral Arene Chromium Tricarbonyl Complexes as Enantioselective Catalysts: Highly Selective 1,2-Alkyl Additions to Aldehydes
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The preparation of a rationally designed catalyst system derived from norephedrine is reported.The key stereodirective element emanates from a chromium tricarbonyl group complexed to one face of the aryl ring.The catalysts mediate the addition of diethyl zinc to a variety of aldehydes with extremely high enantioselectivity.Key Words: enantioselective catalyst; norephedrine; arene chromium tricarbonyl; diethyl zinc; chiral 1,2-addition
- Heaton, Steven B.,Jones, Graham B.
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p. 1693 - 1696
(2007/10/02)
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- Chiral N,N-Dialkylnorephedrines as Catalysts of the Highly Enantioselective Addition of Dialkylzincs to Aliphatic and Aromatic Aldehydes. The Asymmetric Synthesis of Secondary Aliphatic and Aromatic Alcohols of High Optical Purity
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The chiral N,N-dialkylnorephedrine-catalyzed addition of dialkylzincs to aliphatic and aromatic aldehydes afforded secondary alcohols of high optical purity (to > 95percent ee).Among the N,N-di(primary alkyl)norephedrines, N,N-di-n-butylnorephedrine (DBNE, 3d) was found to be the most effective catalyst. 1-Phenyl-2-(1-pyrrolidinyl)propan-1-ol (3i) and N,N-diallylnorephedrine (3j) were also highly effective catalysts.The method described provides optically active secondary aliphatic alcohols of high optical purity which cannot be prepared by conventional methods.
- Soai, Kenso,Yokoyama, Shuji,Hayasaka, Tomoiki
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p. 4264 - 4268
(2007/10/02)
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