Asymmetric Protonation of Cumulenolates: Synthesis of Allenyl Aldehydes Facilitated by an Organomanganese Auxiliary
journal contributionposted on 29.02.2016, 16:33 by Animesh Roy, Bilal A. Bhat, Salvatore D. Lepore
Chiral ammonium salts were used to catalyze the isomerization of organomanganese-complexed alkynyl aldehydes to chiral allenal building blocks in moderate to good enantiomeric excesses. Normally, conjugated alkynyl aldehydes do not isomerize to their thermodynamically less stable allene isomers. However, with a manganese auxiliary in place to promote allene formation, asymmetric protonation of cumulenolate intermediates was realized using a variety of cinchonidinium salts in a weakly basic biphasic reaction system. Optimal results were realized using a novel cinchonidinium geranyl derivative with its C-9 hydroxyl group playing a crucial role in enantioselectivity.
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enantioselectivitycinchonidinium saltsnovel cinchonidinium geranylenantiomeric excessescatalyzebiphasic reaction systemOptimal resultsvarietyallene formationcumulenolate intermediatesSynthesiAsymmetric Protonationalkynyl aldehydeschiral allenal building blocksallene isomershydroxylroleAllenyl Aldehydes FacilitatedprotonationOrganomanganese Auxiliary Chiral ammonium saltsisomerizeisomerizationCumulenolate