HIGH ACTIVATION OF CARBONYL GROUPS WITH B IDENTATE LEWIS-ACID CATALYSTS

Carbonyl group is one of the most popular and yet ubiquitous functiona lity of organic compounds and often encountered in biomolecules such a s peptides and lipids, playing a crucial role to organize three dimens ional intermolecular associations. For organic chemists, it always app ears as an extremely useful functional group to be manipulated and eit her Bronsted acids or Lewis acids are routinely employed for the activ ation of carbonyls in electrophilic substitution reactions, where the acids preferably coordinate to one of the two carbonyl lone pairs. Bei ng close to the core of Lewis acid chemistry, we have been interested some time in the possibility of double electrophilic activation of car bonyl functionality by designing bidentate Lewis acid catalysts which could simultaneously coordinate to both of the carbonyl lone pairs wit h two metals. In this review, we describe the development of bidentate aluminum and titanium Lewis acids, and evaluation of their reactivity and selectivity in organic synthesis. Further, the applications of ou r concept to the elaboration of new synthetic methodologies are also d iscussed. Those include neutral allylation of carbonyls with bidentate tin compounds by using chelation-induced Lewis acidity, and activatio n of bidentate bis(silyl) compounds with a fluoride anion.