Coupling reactions Trialkylaluminums

Hirota, K. Kitade, Y. Kanbe, Y. Maki, Y. Convenient Method for the Synthesis of C-Alkylated Purine Nucleosides Palladium-Catalyzed Cross-Coupling Reaction of Halopurine Nucleosides with Trialkylaluminums. J. Org. Chem. 1992, 57, 5268-5270. 

With the development of the cross coupling methodology, many 6-C-substituted purines have been prepared in the past decade. Thus, 6 halopurine derivatives react with arylmagnesium halides,25 alkyl(aryl)zinc or tin reagents,26 trialkylaluminum,27 or alkylcuprates28 to give the 6-alkylpurine derivatives. Also a reverse approach based on the reaction of purine-6-zinc iodide with aryl or vinyl halides has recently been described.29 For the synthesis of 6-arylpurines, an alternative approach makes use of radical photochemical reactions of adenine derivatives with aromatic compounds,30 but this method is very unselective and for substituted benzenes, mixtures of ortho-, meta-, and para substituted derivatives were obtained. 

However, allylation of alkylthioallylcopper compounds, generated in ether from alkylthioallyllithium and Cul at -78 °C (the synthesis of phenylthio analogs fails ), affords exclusively - 7-7 (tail-to-tail) coupled products (Scheme 27), whereas alkylthio allylic aluminum and boron ate complexes, readily available from reaction of alkylthioallyllithium compounds with trialkylaluminum and... 

---