3.3- diarylalkanal arene

Diarylalkanes are important structural motifs that can be found in a variety of pharmaceuticals, agrochemicals and fine chemicals. Examples are papaverin, avrainvilleol and beclobrate (Scheme 2). Traditionally, 1,1-diarylalkanes can be prepared from benzyl halides and the corresponding arenes under Friedel-Crafts-type conditions. 

Similar to Rueping s procedure, Hua and coworkers developed a BiCl3-catalyzed synthesis of 1,1-diarylalkanes also starting from electron-rich arenes and styrenes [68]. They found that styrenes 37 could be transformed to the substituted cyclopentanes 39 if catalytic amounts BiCl3 were applied (Scheme 30). This reaction is believed to proceed via an intermolecular ene-reaction between styrene and the carbocationic intermediate I, followed by an intramolecular Friedel-Crafts alkylation of the resulting intermediate II. 

Again FeCl3-6H20 is the catalyst of choice for the benzylation of o-xylene by 4-chlorostyrene (Table 6.2). This iron-catalyzed arylation reaction of styrenes allows the synthesis of a wide variety of 1,1-diarylalkanes employing various styrenes and diverse arenes. Scheme 6.15 illustrates selected examples of successfully synthesized 1,1-diarylalkanes and Table 6.3 shows the diversity of different substituted styrenes employed as benzylating agents. 

Iron salts (e.g. FeCls) have been identified as new catalysts for intramolecular hydroamination. A number of olefinic tosylamides underwent the reaction at 80 °C to form the corresponding the N-tosylpyrrolidine derivatives in good yield.63 The same salt can also catalyse Markovnikov addition of electron-rich arenes and heteroarenes to styrenes, giving rise to 1,1-diarylalkanes at 80 °C.64... 

Friedel-Crafts reaction. Active arenes (phenols, aryl ethers, aryl sulhdes,...) are alkylated by A-tosyl aldimines (and benzylamines) such that 1,1-diarylalkanes result, with promotion by Bi2(S04)3-Me3SiCl. ... 

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