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

Abstract

TADDOLs (or,cc,cc',a'-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(OCHMe,),) to generate polymer heads incorporating Ti-TADDOLate centers (Figs. f and 2) for enantioselective catalysis (Et,Zn addition to PhCHO). Compared with conventionally polymerattached, insoluble Ti-TADDOLates (cf. 3), the new materials have a much higher catalytic activity, rather close to that of soluble analogs (Fig. 3).

Dendritic TADDOLs: Synthesis, Characterization and Use in the Catalytic Enantioselective Addition of Et2Zn to Benzaldehyde

“…inverse or unimolecular micelle), simpler recovery and separation from products, or better performance when incorporated in polymers. [12] Experiments along these lines are currently being performed in our laboratory.…”

“…[9] Finally, it is not to be expected that remote chiral units in a dendrimer have a strong influence on the stereoselectivity with which a catalytic site performs. [10] In view of possible applications of derivatives of TADDOL ((R,R)-a,a,a',a'-tetraaryl-1,3-dioxolane-4,5-dimethanol, Figure 1) [11] in membrane reactors and in dendritically crosslinked polymer particles, [12] we have now prepared compounds with the propeller-type [13] TADDOL moiety in the center [14] carrying four dendritic arms. These, in turn, were of three different types: ¹classicalª achiral Fre  chet dendrimer Figure 1.…”

TADDOLs, Their Derivatives, and TADDOL Analogues: Versatile Chiral Auxiliaries

“…The dendritic derivative with eight peripheral styryl groups is a novelty in two respects; quite apart from its TADDOL nucleus, it was the first dendritic cross-linking agent ever prepared for styrene, and this also represents the first occasion on which a chiral ligand-and thus an enantioselective catalytic agent (see below)-had been incorporated dendritically into a polymer. [371,376] The cross-linking suspension ± copolymerization of styryl-TADDOLs with styrene under standard conditions [375] resulted in nicely formed spheres that displayed good swelling capacity and a remarkable set of properties [71,371,372] (Figure 15). Figure 14.…”

Synthesis of enantiopure 2‐(aminoalkyl)phenol derivatives and their application as catalysts in stereoselective reactions

“…and also metal complex catalysts. [107][108][109][110][111][112] It is interesting therefore to develop much simpler and readily available ligand, possessing high catalytic effect, that features a deep chiral pocket after complexation with the organozinc reagent, in order to realize an efficient catalytic and enantioselective process. Among the other, 2-(aminoalkyl)phenols 20 and 1-(aminoalkyl)naphthols have been successfully applied in this sense, owing to their particular shape and the second ones have been also the object of patent for enantioselective addition reactions to carbonyl compounds.…”