Isovaleraldehyde aldol reaction

Polymeric Evans auxiliary 76 was also applied to aldol reactions2 4 (Scheme 1.6.37). In a model reaction, immobilised dihydrocinnamic acid was converted into the boron enolate and reacted with isovaleraldehyde. Products were released by treatment of the resin with NaOMe. The p-hydroxy ester 79 was obtained in a 20 1 diasteromeric ratio, along with some ester 80 derived from unreacted starting material. 

Although treatment of enolate 184 with isovaleraldehyde produced no reaction, addition of the enolate to a solution of isovaleraldehyde precom-plexed with TiCl4 provided the anti aldol product 187 in 97% yield as a single isomer (by HPLC and NMR) as shown in Scheme 2.16. 

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