Stereodivergent Quaternization of 2-Alkyl-2-p-tolylsulfinylacetonitriles: NMR Spectroscopic Evidence of Planar and Pyramidal Benzylic Carbanions

Enantiomerically enriched α,α‐disubstituted phenylacetonitriles have been readily prepared by stereoselective quaternization of 2‐alkyl‐2‐[2‐(p‐tolylsulfinyl)phenyl]acetonitriles with different alkylating electrophiles in the presence of bases. The use of potassium hexamethyldisilazane (KHMDS)/[18]c...

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Bibliographic Details
Published in:Chemistry : a European journal 2010-06, Vol.16 (21), p.6317-6325
Main Authors: García Ruano, José Luis, Martín-Castro, Ana M., Tato, Francisco, Torrente, Esther, Poveda, Ana M.
Format: Article
Language:English
Subjects:
Acetonitriles - chemistry
Alkylation
Anions - chemistry
asymmetric synthesis
carbanions
Carbon - chemistry
Chemistry
chirality
diastereoselectivity
Enrichment
Ethers
Halides
Isomers
Magnetic Resonance Spectroscopy
NMR
NMR spectroscopy
Nuclear magnetic resonance
Potassium
Spectroscopic analysis
Spectroscopy
Stereoisomerism
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Summary:Enantiomerically enriched α,α‐disubstituted phenylacetonitriles have been readily prepared by stereoselective quaternization of 2‐alkyl‐2‐[2‐(p‐tolylsulfinyl)phenyl]acetonitriles with different alkylating electrophiles in the presence of bases. The use of potassium hexamethyldisilazane (KHMDS)/[18]crown‐6 ether and NHMDS with alkyl halides afforded S,SS and R,SS diastereoisomers, respectively, in high enantiomeric purities, thus providing stereodivergent processes for synthesizing both isomers. The dependence of the stereochemical course of the reactions on the experimental conditions (mainly on the counterion) has been rationalized by assuming a planar or pyramidal structure for the benzylic carbanions. This hypothesis has been supported by NMR spectroscopic studies, which permit one to assign a chelated pyramidal structure to the sodium benzylic carbanions and an almost planar naked carbanionic structure to the potassium benzylic carbanions generated in the presence of [18]crown‐6 ether. Remote stereocontrol: Enantiomerically enriched α,α‐disubstituted phenylacetonitriles were prepared by stereoselective quaternization of 2‐alkyl‐2‐[2‐(p‐tolylsulfinyl)phenyl]acetonitriles with different alkyl halides in the presence of bases (see scheme). The stereochemical course of the reactions has been rationalized and supported by NMR spectroscopic studies.
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.200903521