Bis(hydroxyphenyloxazolinato)-titanium(IV) and -zirconium(IV) triflates as novel transition metal-based Lewis acids
作者:Pier Giorgio Cozzi、Carlo Floriani
DOI:10.1039/p19950002557
日期:——
The preparation of novel titanium, 3, and zirconium, 4, organometallic Lewis acids by treatment of the readily available [M(L)(2)(CI)(2)] complexes (M = Ti, Zr; L = hydroxyphenyl-4,5-dihydrooxazole) with AgOSO2CF3 are described. The new homogeneous organometallic Lewis acids, prepared in situ, are active in promoting aldol reactions, additions to imines and catalytic allylations. In addition, some examples of the use of 3 and 4 in other reactions (i. e. Mukaiyama-Michael reaction,addition of Me(3)SiCN, Diels-Alder, and hetero Diels-Alder reaction) are presented. Some mechanistic studies on the:aldol reaction and on the catalytic allylation have been performed in order to show some of the characteristics of the present Lewis acid system.
Al3+ ion-exchanged montmorillonite efficiently catalyzes the aldol reactions of silyl ketene acetals with carbonylcompounds and acetals. The optimum preparation of the effective montmorillonite catalyst is described.