Control of regio-, diastereo-, 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 different nitrones 2 by the application of a TiX₂(TADDOLato)] complex as the catalyst was developed (TADDOL = α,α,α′,α′-tetraaryl-1,3-dioxolane-4,5-dimethanol). In the absence of a catalyst, the 1,3-dipolar cycloaddition of 4 with 2 proceeded to give a mixture of regioisomers, whereas, in the presence of a catalyst, the regioselectivity of the reaction could be controlled. Three asymmetric TiX₂(TADDOLato)] catalysts were tested, and it was found that use of the Ti(OTs)₂(TADDOLato)] complex gave complete regioselectivity, high ‘endo’-selectivities (> 90% d.e.), and enantioselectivities corresponding to 48–70% e.e.