CONTROL OF REGIOSELECTIVITY, DIASTEREOSELECTIVITY, AND ENANTIOSELECTIVITY IN THE [TI(OTS)(2)(TADDOLATO)]-CATALYZED 1,3-DIPOLAR CYCLOADDITION REACTION BETWEEN 3-ACRYLOYLOXAZOLIDIN-2-ONE AND NITRONES

Catalytic control of regio-, diastereo-, and enantioselectivity in the 1,3-dipolar cycloaddition of 3-acryl-oyloxazolidin-2-one (4) with dif ferent nitrones 2 by the application of a [TiX2(TADDOLato)] complex as the catalyst was developed (TADDOL = a',alpha'-tetraaryl-1,3-dioxolan e-4,5-dimethanol). In the absence of a catalyst, the 1,3-dipolar cyclo addition of 4 with 2 proceeded to give a mixture of regioisomers, wher eas, in the presence of a catalyst, the regioselectivity of the reacti on could be controlled. Three asymmetric [TiX2(TADDOLato)] catalysts w ere tested, and it was found that use of the [Ti(OTs)(2)(TADDOLato)] c omplex gave complete regioselectivity high 'endo'-selectivities (> 90% d.e.), and enantioselectivities corresponding to 48-70% e.e.