BF₃·OEt₂-mediated syn-selective Meyer–Schuster rearrangement of phenoxy propargyl alcohols for Z-β-aryl-α,β-unsaturated esters

Abstract

Synthesis of Z-β-aryl-α,β-unsaturated esters from readily available 1-aryl-3-phenoxy propargyl alcohols is achieved via a BF3-mediated syn-selective Meyer-Schuster rearrangement under ambient conditions. The reaction mechanism is postulated to involve an electrophilic borylation of an allene intermediate as the key step to kinetically control the stereoselectivity.

Phosphorus-Recycling Wittig Reaction: Design and Facile Synthesis of a Fluorous Phosphine and Its Reusable Process in the Wittig Reaction

“…[ Z -Isomer (CAS no. 97585-04-1)]: 1 H NMR (400 MHz, CDCl 3 ) δ 7.52 (d, J = 8.2 Hz, 2H), 7.16 (d, J = 8.2 Hz, 2H), 6.90 (d, J = 12.8 Hz, 1H), 5.89 (d, J = 12.8 Hz, 1H), 4.18 (q, J = 7.0 Hz, 2H), 2.36 (s, 3H), 1.26 (t, J = 7.3 Hz, 3H).…”

Recent Developments in the Meyer‐Schuster Rearrangement

“…On the other hand, BF 3 .OEt 2 11 has been used with phenoxy propargylic alcohols to obtain, with a good stereoselectivity, the Z ‐conjugated esters. A mechanism involving an electrophilic borylation of an allene intermediate has been proposed to rationalize this stereoselectivity [16] . The same catalyst has been also used starting from fluoroalkylated propargylic alcohols, leading to a series of β‐fluoroalkyl‐α,β‐enones in moderate to good yields and an excellent E ‐stereoselectivity [17] .…”

“…A mechanism involving an electrophilic borylation of an allene intermediate has been proposed to rationalize this stereoselectivity. [16] The same catalyst has been also used starting from fluoroalkylated propargylic alcohols, leading to a series of β-fluoroalkyl-α,β-enones in moderate to good yields and an excellent E-stereoselectivity. [17] MSR was also effectively catalyzed by methyl triflate 12 in trifluoroethanol (TFE) to obtain a broad scope of conjugated E-enals and Eenones in fair to excellent yields.…”

Oxygen as a Heteroatom in Propargylic Alcohols: Reactivity, Selectivity, and Applications

“…Cis-unsaturated esters are the key synthetic intermediates, and very few synthetic literature reports are available, which are often limited either by multi-steps or a mixture of cis-trans isomerizations. In 2016, our group reported BF 3 .OEt 2 -mediated syn-selective MSR of phenoxy propargyl alcohols for the synthesis of Z-β-aryl-α, β-unsaturated esters [26] (Scheme 17). A series of Lewis acid BF 3 .OEt 2, TMSCl, Ti(O i Pr) 4 , Bi(OTf) 3 , Hg(OTf) 2 , La(OTf) 2 , FeCl 2 , AgOTf, Yb(OTf) 3 , Cu(OTf) 2 and Zn(OTf) 2 were screened, out of these, BF 3 .OEt 2 in ethanol and dioxane (1 : 1 mixture) was the best choice for the complete conversion and produced Z-α, β-unsaturated ethoxy ester as a major isomer.…”