Abstract
The development of efficient Friedel–Crafts alkylations of arenes and heteroarenes using only catalytic amounts of a Lewis acid has gained much attention over the last decade. The new catalytic approaches described in this review are favoured over classical Friedel–Crafts conditions as benzyl-, propargyl- and allyl alcohols, or styrenes, can be used instead of toxic benzyl halides. Additionally, only low catalyst loadings are needed to provide a wide range of products. Following a short introduction about the origin and classical definition of the Friedel–Crafts reaction, the review will describe the different environmentally benign substrates which can be applied today as an approach towards greener processes. Additionally, the first diastereoselective and enantioselective Friedel–Crafts-type alkylations will be highlighted.
Highlights
In 1887 Charles Friedel and James Mason Crafts isolated amylbenzene after the treatment of amyl chloride with AlCl3 in benzene (Scheme 1) [1]. This was one of the first descriptions of a Lewis acid used in organic synthesis and the first example of what was later to be called Friedel–Crafts alkylation (FC alkylation) after its inventors
Today Friedel–Crafts alkylations remain the method of choice for the alkylation of arenes and heteroarenes
Despite the great importance of the Friedel–Crafts alkylation for organic synthesis it has major drawbacks since stoichiometric or super stoichiometric amounts of a Lewis acid or Brønsted acid and toxic alkyl halides have to be utilized leading to vast amounts of salt side products
Summary
Received: 10 September 2009 Accepted: 17 November 2009 Published: 20 January 2010. Keywords: allyl alcohols; arene; asymmetric Friedel–Crafts reaction; benzyl alcohols; Friedel–Crafts alkylation; green chemistry; hydroalkylation; hydroarylation; Lewis-acid catalysis; propargyl alcohols. Received: 10 September 2009 Accepted: 17 November 2009 Published: 20 January 2010
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