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Versatile Friedel–Crafts‐Type Alkylation of Benzene Derivatives Using a Molybdenum Complex/ ortho ‐Chloranil Catalytic System
Author(s) -
Yamamoto Yoshihiko,
Itonaga Kouhei
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200801105
Subject(s) - chloranil , chemistry , alkylation , catalysis , benzene , molybdenum , friedel–crafts reaction , medicinal chemistry , phenylacetylene , organic chemistry , cyclopentadienyl complex , electrophile
A variety of molybdenum complexes catalyze Friedel–Crafts‐type alkylation reactions of benzene derivatives with alkenes and alcohols in the presence of an organic oxidant, o ‐chloranil. The utilization of [Mo(CO) 6 ] and two equivalents of o ‐chloranil catalytically furnished the hydroarylation product of norbornene with p ‐xylene at 80 °C, whereas [Cr(CO) 6 ] and [W(CO) 6 ] failed to catalyze the same reaction, thus indicating the importance of the molybdenum source. The best results were obtained when a molybdenum(II) complex [CpMoCl(CO) 3 ] (Cp=cyclopentadienyl) was used as a precatalyst. The hydroarylation reactions also took place with styrenes, cyclohexenes, and 1‐hexene as olefin substrates. The electrophilic‐substitution mechanism was proposed on the basis of the ortho / para selectivities and the Markovnikov selectivities observed for the hydroarylation products. Our hypothesis was further corroborated by the fact that in the presence of the [CpMoCl(CO) 3 ]/ o ‐chloranil catalytic system, secondary, benzylic, or allylic alcohols participated in the alkylation of benzenes with similar selectivities.