1,8-biphenylenediol catalysts

TABLE 14. Some Diels-Alder reactions catalysed by the biphenylenediol catalyst (cat) 9175 Reaction Conditions Product formation (%)... 

The strong dependence of the reaction rate on the catalyst concentration relative to control experiments in which the amino-hydrogen atoms of 7 were substituted by methyl groups demonstrate that hydrogen bonding represents the major interaction responsible for the observed accelerations. Diels-Alder reactions are also accelerated by hydrogen-bond donors. It was shown that a biphenylenediol 9 is able to catalyse [4 + 2]-cycloadditions of cyclopentadiene, 2,3-dimethylbutadiene and other simple dienes with various a,fi-unsaturated carbonyl compounds (Table 14)175. 

Maruoka and co-workers reported a conceptually new MPV reduction system based on bidentate Lewis-acid chemistry [29]. The initial formation of bidentate aluminum catalyst 9 derived from (2,7-dimethyl-l,8-biphenylenedioxy)bis(dimethylalu-minum) (8 prepared from 2,7-dimethyl-l,8-biphenylenediol and 2 equiv. MesAl) and i-PrOH (4 equiv.), followed by treatment of benzaldehyde with the in situ generated (2,7-dimethyl-l,8-biphenylenedioxy)bis(diisopropoxyaluminum) (9) at room temperature instantaneously produced the reduced benzyl alcohol almost quantitatively (Table 2, entry 2). Even with 5 mol% catalyst 9 the reduction proceeds quite smoothly at room temperature to furnish benzyl alcohol in 81 % yield after 1 h (Table 2, entry 3). This remarkable efficiency can be ascribed to the double electrophilic activation of carbonyls by the bidentate aluminum catalyst (Sch. 7). 

Hine, J., Linden, S.M. and Kanagasabapathy, V.M. (1985) 1,8-Biphenylenediol is a double-hydrogen-bonding catalyst for reaction of an epoxide with a nucleophile. Journal of the... 

Another 0,0 -bidendate ligand class with a more constrained bisphenol backbone based on 2,7-dimethyl-l,8-biphenylenediol has been comprehensively investigated by the group of Ooi and Maruoka. The ligands were reacted with trimethyl aluminium as precursor to afford, after controlled alcoholysis, highly efficient aluminium catalysts, as shown in Scheme 18.14. ... 

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