Abstract
The isomerization of dienyl alcohols and polyenyl alkyl ethers catalyzed by TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene) under metal-free conditions is presented. Two reaction pathways have been obser...
Highlights
The isomerization of allylic alcohols into carbonyl compounds is a fundamental and powerful tool in organic synthesis
In 2016, we reported that the isomerization of electron-poor allylic alcohols and allylic ethers could be mediated by a simple base, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), through a stereospecific [1,3]-proton shift (Scheme 1b)
We describe the first examples of the isomerization of conjugated allylic alcohols and ethers using a base catalyst (Scheme 1c)
Summary
We describe the first examples of the isomerization of conjugated allylic alcohols and ethers using a base catalyst (Scheme 1c). When ((1E,3E)-5-methoxypenta-1,3-diene-1,5-diyl)dibenzene (3a) was treated with TBD (20 mol %) in toluene at 60 °C overnight, interestingly, and in contrast to the reaction of conjugated dienyl alcohols, diene 4a formed as the major product as a result of a formal [1,5]-proton shift ([1,5]: [1,3] > 20:1). These results suggest that in both cases the reaction starts with a rate-determining deprotonation at C-1. The calculated energies of the ratedetermining transition states (TSI−II and TSI−II′, Figure 1) increase by 0.6−0.9 kcal/mol when H is replaced with D (see the Supporting Information for further details) This explains the KIE and the lower rates observed for the deuterated substrate 3a.
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