Titanium(IV) Bromide and Boron(III) Tribromide Promoted Baylis-Hillman Reactions of Arylaldehydes with But-3-yn-2-one

Abstract

The reaction of arylaldehydes with but-3-yn-2-one in the presence of the Lewis acids titanium(IV) bromide (TiBr 4 ) or boron(III) tribromide (BBr 3 ) (1.4 equiv.) can be drastically affected by the reaction temperature. When the reaction was carried out at À 208, the brominated compound 1 was obtained as the major product. However, when the reaction was carried out at room temperature (208), both the brominated compound 1 and dibrominated compound 2 were formed as major products. The substituent on the phenyl ring can affect the (E)/ (Z) ratio. Moreover, with 2 as the substrate, the Pd-catalyzed allylic substitution and Suzuki-type coupling reaction have been examined.

Recent Advances in the Baylis−Hillman Reaction and Applications

“…Shi and Wang also examined the reaction between but-3-yn-2-one with aryl aldehydes in the presence of TiBr 4 or BBr 3 . At −20 °C, β-bromo Baylis−Hillman adducts were formed with high E -selectivity (in the case of 2-(NO 2 )Ph and 3-(NO 2 )Ph, Z -selectivity is favored due to steric factors), whereas at room temperature dibromides 116 were obtained along with β-bromo Baylis−Hillman adducts (Scheme ).…”

Titanium Enolate Chemistry at the Beginning of the 21st Century

“…The far less reactive methyl prop‐2‐ynoate and HC≡C–CN gave β,β‐dibromo compounds 83 (Scheme ). Simultaneous research conducted by Li and co‐workers125b showed that the excesses of the ketone and TiBr 4 could be lowered to give “aldol adducts” 87 with various aldehydes, with excellent E selectivity and moderate yields. TiF 4 can also promote the MBH reaction, giving exclusively products of type 88 126…”