Abstract
Asymmetric alkynylation reactions to mono-, di-, and trisubstituted aromatic aldehydes have been accomplished in good yields and with a range of selectivities. For salicylaldehyde derivatives both the yield and the enantioselectivity of the alkynylation reaction appears to depend not only upon the electron-donating/electron-withdrawing nature of substituents but also upon their position in the ring relative to the carbonyl. For benzaldehyde derivatives this observation is exemplified with nitrobenzaldehyde wherein asymmetric alkynylation with 3-nitrobenzaldehyde occurs in virtually quantitative yield and enantioselectivity. In contrast our attempts at asymmetric alkynylations with 4-nitrobenzaldehyde failed.
Key words
asymmetric alkynylation reaction - aromatic aldehydes -
N- methylephedrine - substituent effects - position effects
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15 16 CCDC 628668 [(R )-10 ] and CCDC 628669 [(R )-15 ] contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
17 We have used both forms of N -methylephedrine in some selected examples in our studies in an attempt to obtain crystals suitable for X-ray analysis. We observed a significant difference in crystal morphology between enantiomeric propargyl alcohols.
18 In addition to the differences in the 1 H NMR spectra of these enantiomers, we observed differences in mp 90.5-90.7 °C (R
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