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Conjugate Addition of Lithiated ( S )‐4‐Isopropyl‐3‐ [(methylthio)methyl]‐5,5‐diphenyloxazolidin‐2‐one to Cinnamoyl Derivatives: Preparation of Enantiomerically Pure 1,4‐Diols
Author(s) -
Gaul Christoph,
Seebach Dieter
Publication year - 2002
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(200203)85:3<772::aid-hlca772>3.0.co;2-i
Subject(s) - chemistry , stereocenter , cinnamates , isopropyl , adduct , medicinal chemistry , conjugate , derivative (finance) , stereochemistry , organic chemistry , enantioselective synthesis , catalysis , mathematics , financial economics , mathematical analysis , economics
The Li derivative of ( S )‐4‐isopropyl‐3‐[(methylthio)methyl]‐5,5‐diphenyloxazolidin‐2‐one (Li‐ 2 ; synthetically equivalent to a chiral formyl anion) adds to enones and enoates in a 1,4‐fashion. Best results are obtained with 1,3‐diarylpropenones (chalcones; Scheme 2 ), trityl enones, and 2,6‐di( tert ‐butyl)‐4‐methoxyphenyl cinnamates ( Scheme 3 ), with yields up to 80% and diastereoselectivities up to and above 99 : 1 of the products ( 5a – f and 8a , b , e ) containing three stereogenic centers! X‐Ray crystal‐structure analysis reveals that the C,C‐bond formation occurs preferentially with relative topicity ul ( Re / Si ; Fig. 2 ). The MeS group of the 1,4‐adducts can be replaced by RO groups in Hg 2+ ‐assisted substitutions, with subsequent removal and facile recovery of the chiral auxiliary ( Schemes 4 – 6 ). 4‐Hydroxycarbonyl derivatives (‘homoaldols') and mono‐, di‐, and trisubstituted 1,4‐diols are, thus, accessible in enantiomerically pure forms ( cf. 15, 16 , and 18 – 20 ).