Abstract
AbstractA bifunctional iminophosphorane (BIMP)‐catalysed enantioselective synthesis of α,β‐unsaturated cyclohexenones through a facially selective 1,3‐prototropic shift of β,γ‐unsaturated prochiral isomers, under mild reaction conditions and in short reaction times, on a range of structurally diverse substrates, is reported. α,β‐Unsaturated cyclohexenone products primed for downstream derivatisation were obtained in high yields (up to 99 %) and consistently high enantioselectivity (up to 99 % ee). Computational studies into the reaction mechanism and origins of enantioselectivity, including multivariate linear regression of TS energy, were carried out and the obtained data were found to be in good agreement with experimental findings.
Highlights
A bifunctional iminophosphorane (BIMP)-catalysed enantioselective synthesis of a,b-unsaturated cyclohexenones through a facially selective 1,3-prototropic shift of b,gunsaturated prochiral isomers, under mild reaction conditions and in short reaction times, on a range of structurally diverse substrates, is reported. a,b-Unsaturated cyclohexenone products primed for downstream derivatisation were obtained in high yields and consistently high enantioselectivity
Guided by our previous work, we initially investigated a range of 1st generation BIMP catalysts (3 a–d), including catalyst 3 a, which was used in the total synthesis of (À)-himalensine A.[8]
In further exploration of the reaction scope, we looked at the effect of pendant-heteroatom variance on reactivity and Scheme 2
Summary
A bifunctional iminophosphorane (BIMP)-catalysed enantioselective synthesis of a,b-unsaturated cyclohexenones through a facially selective 1,3-prototropic shift of b,gunsaturated prochiral isomers, under mild reaction conditions and in short reaction times, on a range of structurally diverse substrates, is reported. a,b-Unsaturated cyclohexenone products primed for downstream derivatisation were obtained in high yields (up to 99 %) and consistently high enantioselectivity (up to 99 % ee). We turned our attention to P(PMP)3-derived 2nd generation BIMP catalysts, and with catalyst 3 e, substrate 1 a underwent the 1,3-prototropic shift in decent yield (67 %), enantiocontrol (18 % ee) remained poor.
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