Grignard polymer-bound

The reaction of a polymer-bound imidazole-iV-carboxylate with a Grignard reagent leads to an ester [93]... 

The halogen-magnesium exchange reaction can be easily applied to solid-phase synthesis, affording polymer-bound Grignard reagent, otherwise unavailable (Scheme 27). 

Addition of Grignard Reagents to Polymer-Bound Carbonyl Compounds and Imines... 

The addition of an organomagnesium reagent to a polymer-bound aldehyde, ketone, or ester to form an alcohol, is the most common appHcation of Grignard reagents on solid phase and with many examples in the literature. A review by Franz n covers the earlier reports up to 1999 [45]. In many cases, the Grignard reaction has been used to test the compatibility of new Hnkers towards various reaction conditions. One such example concerns a modified... 

The resulting active end-groups have a covalent structure, rather than ionic, with tetrahedrally bound ligands persisting unaltered during the lifetime of the polymeric chains 46). This persistence of the various initially formed structures accounts for the multimodal distribution of the molecular sizes of polymers initiated by Grignard compounds46). 

Kawana et al. used xylofuranose derivates as chiral auxiliaries [7, 13], Through its primary hydroxy function, the auxiliary was loaded to the polystyrene resin. Esterification of the immobilized auxiliary 8 gave a-keto esters. Subsequent nucleophilic additions of Grignard reagents afforded resin-bound a-hydroxy esters. Subsequent saponification afforded the chiral a-hydroxy acids 9 (Scheme 12.5) in 18-84% yields and 36-65% enantiomeric excesses. The recovered polymer supported chiral auxiliaries could be reused without decrease of enantioselectivity. 

Synthesis of Vitamin D3 Core 248 Phosphine oxide 245 (1.1 equiv) was dissolved in anhydrous THF, cooled to —50°C, and treated with nBuLi (1.0 equiv) under argon. The mixture was then transferred via cannula to a solution of resin-bound ketone 244 (0.72 equiv) in anhydrous THF and reacted at —40°C to — 10°C for 3 hours to yield immobilized triene 246. Concomitant alkylation and cleavage from the polymer-support occurred via a copper-promoted Grignard reaction with 247 at room temperature for 3 hours. The crude protected product was then immediately treated with CSA in methanol and water at room temperature for 6 hours to afford vitamin D3 analog 248 in 47% yield (from 244). 

---