Acetalisation acid catalysed

The formation of acyclic dialkyl acetals is generally restricted to aldehydes and more reactive ketones. The most common methods involve acid-catalysed acet-alisation using an alcohol solvent (usually methanol) or, more usually, by trans-acetalisation, which is preferred because it provides the most efficient means for removing water liberated in the reaction. Scheme 2.58 illustrates acetal formation in the presence of an add-sensitive jV-Boc group catalysed by... 

Scheme 7.17 L,L-Prolylprolinol/3-fluorobenzoic acid catalysed tandem stereoselective Michael/acetalisation process to chroman-2-ols.

The synthesis starts with the known lactone 21 (ref. 14) which is easily obtained from ( )-quinic acid (20) by treatment with acetone in the presence of a trace of acid. After benzoylation and removal of the acetal protecting groups, 21 yielded the diol 22 which was converted into the cyclohexene derivative 23 by application of Eastwood s method (ref. 15). Reduction of 23 with LiAlH followed by acid catalysed acetalisation with 2,2-dimethoxypropane afforded the cyclohexe-nol derivative 24. 

New developments of catalytic reactions with tin(iv) oxide are connected to the acid-catalysed biomass transformation. Acetalisation of glycerol with acetone in a 1/1 molar ratio was catalysed by tin(iv) oxide under solventless conditions at room temperature. The conversion could be greatly increased from 15 to 60% by the addition of 10 wt% of M0O3 (Scheme 21.6). It was further shown that molybdenum(vi) oxide led to a larger BET surface area... 

Scheme 7.40 Three-component domino cyclisation-Mannich-type-acetalisation reaction catalysed by chiral phosphoric acid catalysis and gold catalysis.

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