Ammonium bifluoride catalysis

Homogeneous Catalysis with Chiral Quaternary Ammonium Bifluorides 125... 

The efficient homogeneous catalysis of chiral ammonium bifluorides of type 15 has been further utilized for achieving an asymmetric Michael addition of silyl nitronates to a,/ -unsaturated aldehydes. Here, chiral ammonium bifluoride 15b bearing a 3,5-di-tert-butylphenyl group was found to be the catalyst of choice, and the reaction of 16a with trans-cinnamaldehyde under the influence of (R,R)- 15b (2 mol%) in THF at —78 °C produced the 1,4-addition product 18 predominantly (18/19 = 24 1) as a diastereomeric mixture (syn/anti = 78 22) with 85% ee of the major syn isomer (Scheme 4.9). Further, use of toluene as solvent led to almost exclusive formation of the 1,4-adduct (18/19 = 32 1) with similar diastereoselec-tivity (syn/anti = 81 19), and critical enhancement of the enantioselectivity was attained (97% ee) [15]. 

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See also in sourсe #XX -- [ ]

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