Dendritic styryl TADDOLs as novel polymer cross-linkers: First application in an enantioselective Et2Zn addition mediated by a polymer-incorporated titanate

TADDOLs (alpha,alpha,alpha',alpha'-tetraaryl-1,3-dioxolane-4,5-dimethanols) with dendritic branches attached to the aryl groups and with 8 or 16 peripheral styryl double bonds have been synthesized (4 and 5). With these compounds, dendritic molecules were employed for the first time as cross-linkers in a polymerization. The resulting polystyrene was loaded with titanate (Ti(OCHMe2)(4)) to generate polymer beads incorporating Ti-TADDOLate centers (Figs. 1 and 2) for enantioselective catalysis (Et2Zn addition to PhCHO). Compared with conventionally polymer-attached, insoluble Ti-TADDOLates (cf. 3), the new materials have a much higher catalytic activity, rather close to that of soluble analogs (Fig. 3).