Isobutene Friedel-Crafts reaction

Friedel-Crafts alkylation of benzo[6]thiophene has received little attention. The published results, which deserve reexamination, indicate that exclusive 3-substitution occurs in some cases, whereas in others, 2-substitution predominates. Benzo[6]thiophene is alkylated with isopropyl chloride, isopropanol, or propene in the presence of various acid catalysts under a variety of reaction conditions to give a mixture of 2- and 3-isopropylbenzo[6]thiophene in which the 2-isomer predominates (78-92%).358 410 In contrast, alkylation with isobutene in the presence of either 80% sulfuric acid415 or 100% phosphoric acid416 is said to afford exclusively 3-/er<-butylbenzo[6]thiophene in yields of 100 and 75%, respectively. In neither case was the structure of the product rigorously confirmed. Likewise, 3-Jeri-amylbenzo [63-thiophene is the exclusive product of alkylation with tert-amyl alcohol in the presence of stannic chloride414 alkylation with pent-l-ene, hex-l-ene, and a Ci8 propylene polymer is also claimed to give... 

The industrial synthesis of ibuprofen is a well-known case study for green chemistry . [190] The original Boots route, starting from benzene, comprised seven steps, p-lsobutylacetophenone is accessible by alkylation of benzene with isobutene, followed by a Friedel-Crafts acylation with acetic chloride. Homologation to the corresponding aryl-propionaldehyde is achieved by a Darzens reaction. Transformations via the oxime and nitrile, and hydrolysis of the latter, finally give ibuprofen. 

It is possible to graft isobutene onto activated polymer molecules when they can be alkylated in an electrophilic reaction [602-604]. Polystyrene, for instance, is alkylated with Friedel-Crafts catalysts. The grafting is simplified by the presence of halogen atoms in the main polymer chain. Addition of diethylaluminumchloride or triethylaluminum leads to the formation of cations. The graft polymers usually contain between 10 and 60% of isobutene units and feature outstanding elasticity and dimensional stability at higher temperatures. Also, copolymers of isobutene and isoprene, butadiene, styrene, and so on, can be grafted in this manner [605-607]. 

Friedel-Crafts and Other Alkylation Reactions. A variety of r-butyl-substituted aromatics have been prepared with isobutene in the presence of acids (eqs 19-21). Due to steric factors, the regiochemistry is enhanced. Isobutene can be alkylated by benzylic and allylic halides in the presence of Zinc Chloride (eqs 22-24). ... 

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