Study on Selective Dimerization of α-Methylstyrenes Promoted by Ionic Liquids

Abstract

The catalytic systems composed of ionic liquids containing BF 4 -anion and HBF 4 showed high catalytic activity to produce 4-methyl-2,4-diphenyl-1-pentene (MDP-1) or 1,1,3-trimethyl-3-phenylindan (TPI) under different temperature conditions. Up to 90.8% selectivity to MDP-1 with a 98.7% conversion of a-methylstyrene was obtained at 60°C in the presence of [HexMIm]BF 4 -HBF 4 , while exclusive TPI was yielded when the reaction temperature increased to 120°C. Further studies showed that another ionic liquid, [BMIm]Cl Á 2AlCl 3 , could act as an excellent catalyst and solvent for the dimerization of a-methylstyrene to produce TPI. The dimerization of a-methylstyrene catalyzed by [HexMIm]BF 4 -HBF 4 and [BMIm]Cl Á 2AlCl 3 performed the same reaction mechanism and the proton was the active species.

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

“…Since the pioneering work on the use of these ILs for the oligomerization of alkenes by transition-metal complexes (Figure ), ,, a wide range of biphasic oligomerization/polymerization reactions have been reported (Table ). , It should be noted that organo-aluminate and other acidic ILs are active for the oligomerization of alkenes through acid catalysis, ,− but this falls outside the scope of this review.…”

Cationic β‐Scission of C−H and C−C Bonds for Selective Dimerization and Subsequent Sulfur‐Free RAFT Polymerization of α‐Methylstyrene and Isobutylene

“…In particular, selective cationic dimerizations of vinyl and vinylidene compounds via β‐proton elimination have long been investigated by a wide range of researchers working on polymer, organic, catalytic, process, and industrial chemistry because the obtained olefins are useful organic molecules. Among them, α‐methylstyrene (αMS) has been most extensively studied with various acidic catalysts, such as Brønsted and Lewis acids and solid, organometallic, composite, and photocatalysts, as well as anionic and radical catalysts [18–42] . Since αMS dimers have varied structures with internal and external olefins as well as cyclic and indan structures due to the various accompanying reactions, the selective synthesis of a specific dimer provides an additional challenge.…”

One-Pot Synthesis of α-Alkyl Styrene Derivatives

“…All of the above-mentioned synthetic methods have appeared in the literature reflecting the many applications that α-alkyl styrenes can have. For instance, α-alkyl styrenes have been used in Povarov reactions, [6+2] cycloaddition reactions, isomerizations, , selective hydrocarboxylations, dimerizations, , fluorocyclizations, allylic fluorinations, in the synthesis of 2-fluoro-2-phenylalkancil acids, among others. , Therefore, it is valid to say that α-alkyl styrenes have emerged as synthetically useful building blocks. However, despite these various reported synthetic alternatives, it is reasonable to say that a milder, transition metal-free method to synthesize α-alkyl styrenes, with a broader scope, would be extremely useful.…”