Aldol-acetalisation reaction

Later, Ramachary and Sakthidevi reported for the first time the organo-catal)Aic cascade approach to the asymmetric synthesis of functionalised chromans via Barbas-List aldol-acetalisation reaction, as depicted in Scheme 2.28. The reaction of acetone with 2-hydro ybenzaldehyde under trans-4-OH-L-proline-catalysis in NMP as solvent furnished the corresponding aldol/lactol intermediate which upon treatment with p-TSA in methanol in one-pot furnished the selectively frans-2-metho y-2-methyl-chroman-4-ol in 55% yield and 77% ee, as shown in Scheme 2.28. 

Scheme 2.28 Tandem aldol-acetalisation reaction catalysed by chiral 4-hydroxy-proline and p-TSA.

Lanthanide(ni) on ion exchange resins catalyse Mukaiyama aldol reactions in aqueous media, acetalisations, additions of silyl enol ethers to imines, saz-Diels-Alder reactions and the ringopening of epoxides with alcohols as depicted in Scheme 3.6.7. 

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