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Primary-Secondary Diamine Catalysts for Malonate Additions to Enones
Y.-Q. Yang, G. Zhao*
University of Science and Technology of China, Hefei and Shanghai Institute of Organic Chemistry, P. R. of China
22 January 2009 (online)
This work describes the highly enantioselective Michael addition of dibenzyl malonate 2 to enones 1 in the presence of a catalytic amount (20 mol%) of the TFA salt of the novel primary-secondary diamine 3. A broad range of benzylideneacetone derivatives, irrespective of their electronic nature, chalcone, an aliphatic enone, and cyclohexenone were suitable substrates yielding the corresponding products 4 in good to excellent yields (66-99%) and enantiomeric ratios of up to >99.5:0.5. Notably, in contrast to previous studies on the same reaction, the use of two equivalents of the malonate component was sufficient. The authors’ working hypothesis invokes a bifunctional iminium mechanism with the enone being activated as iminium ion (see Scheme, 5).