For the preparation of α,β-unsaturated esters, Horner–Wadsworth–Emmons (HWE) modiﬁcation of the Wittig reaction is a widely used method in organic synthesis. Especially, this reaction is popular for stereoselective olefination of carbonyl compounds which are useful in the synthesis of complex natural products. Till date the HWE reaction has been extensively studied1, however most of the conditions demonstrated for aldehyde and ketone functional group. To the best of our knowledge, only few reports demonstrated with ester group.2,3
Given our interest in finding selective and one pot reactions, and the above situation was prompted us to carry out reductive-HWE reaction with ester group. Recently, we have identified reductive-HWE olifination from ester group via partial reduction followed by Wittig homologation in one pot. In continuation, the present abstract demonstrates HWE olifination with modified and efficient protocol from readily available reagents. As a result, α,β-unsaturated esters were prepared successively form the homologation of esters using LDBBA and n-BuLi under mild conditions (Scheme).
1. K. Kobayashi. et. al. Tetrahedron Letters. 2018, 59, 568-582
2. J. Jeon. et. al. Org. Lett. 2015, 17, 5792-5795.
3. J. Takacs. et. al. Tetrahedron Letters. 1986, 27, 1257-1260