Enantioselective Alkynylation Reactions to Aldehydes: The Effects of Aromatic Substituents upon the Enantioselectivity

Abstract

Asymmetric alkynylation reactions to linear alkyl and substituted aromatic aldehydes have been accomplished in good yields and with a range of selectivities. For aromatic aldehydes we observed that the selectivity of the alkynylation reaction appears to depend upon the substituents on the aromatic ring. Thus with electron-withdrawing substituents both the yield and enantioselectivities were good to excellent. In contrast to this, the presence of electron-donating groups provided excellent conversions; however, these were coupled with poor enantioselectivities.

Key words

asymmetric alkynylation reaction - aromatic aldehydes - N-methylephedrine - organozinc - substituent effects - citronellal

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18

The results from these studies will be disseminated at a later date (although see ref. 4).

19

All compounds provided satisfactory spectral data that were consistent with the assigned structures. For succinctness we have limited the experimental section to a representative example of salicylaldehyde derivatives, e.g. non-substituted, mono- and di-substituted and naphthyl derivatives. Optical rotation data and HPLC retention times are included for all relevant examples.