Coupling of Vinylcyclopropanes with Aldehydes Induced by a TiCl₄/n-Bu₄NI Combination: Synthesis of Conjugated Dienols

Abstract

A TiCl₄/n-Bu₄NI combination induces ring opening coupling of vinylcyclopropanes with aldehydes and acetals. The coupling products obtained with this protocol can be converted into dienes in good yields.

Key words

vinylcyclopropane - titanium tetrachloride - aldehydes - quaternary ammonium halide - diene

References and Notes

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• The coupling reaction between vinylcyclopropanes and aldehydes without ring opening has been reported:
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6

The use of Et₂AlI in place of TiCl₄-n-Bu₄NI provided homoallyl alcohol 2 in moderate yields. The reaction of vinylcyclopropane 1a with benzaldehyde in the presence of Et₂AlI (2.0 equiv) at 0 °C yielded homoallyl alcohol 2a in 68% yield.

7

The apparent reversed E/Z ratio results from change in the priority of R¹ and the 2-hydroxyalkyl group. The sense of the stereoselectivity is the same.

8

The stereochemistry of the ring enlargement products was not assigned. Only two of possible four stereoisomers were detected in the ¹H NMR spectra.

9

Vinylcyclopropanes react with acyl chlorides in the presence of SnCl₄ as a Lewis acid. The use of SnCl₄ in place of TiCl₄-n-Bu₄NI provided β,γ-unsaturated carbonyl compounds in good yield.