Stereoselective Reduction of 2-Methylacetoacetaldehydes Protected as Norephedrine-Derived Oxazolidines: A New Access to Enantiomerically Pure

Alessandra Pasquarello; Giovanni Poli; Carlo Scolastico

doi:10.1055/s-1992-21992

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Synlett 1992; 1992(1): 93-95
DOI: 10.1055/s-1992-21992

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Stereoselective Reduction of 2-Methylacetoacetaldehydes Protected as Norephedrine-Derived Oxazolidines: A New Access to Enantiomerically Pure "Propanal-Type" Aldols

Alessandra Pasquarello^* , Giovanni Poli, Carlo Scolastico

^*Dipartimento di Chimica Organica e Industriale dell'Universitá, Centro CNR per lo Studio delle Sostanze Organiche Naturali, Via Venezian 21, I-20133 Milano, Italy

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Publication Date:
18 September 2002 (online)

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The anti and syn diastereoselective reduction of the 2-methylacetoacetaldehydes (2-methyl-3-oxobutanals) 5 and 6, chirally masked as norephedrine-derived oxazolidines, has been achieved with lithium tri-sec-butylborohydride (Li-s-Bu₃BH) and lithium tri-tert-butoxyaluminohydride [Li(t-BuO)₃AlH], respectively. Subsequent auxiliary removal from the major diastereomers allows access to enantiomerically pure carbonyl-protected [11, 12; 2-(2-hydroxy-1-methylpropyl)-1,3-dithianes] and carbonylfree (15, 16; 3-tert-butyldimethylsiloxy-2-methylbutanals) "propanal-type" aldols.