Chiral Nanoparticles/Lewis Acids as Cooperative Catalysts for Asymmetric 1,4‐Addition of Arylboronic Acids to α,β‐Unsaturated Amides

Abstract

Cooperative catalysts consisting of chiral Rh/Ag nanoparticles and Sc(OTf) 3 have been developed that catalyze asymmetric 1,4-addition reactions of arylboronic acids with a,b-unsaturated amides efficiently. The reaction has been considered one of the most challenging reactions because of the low reactivity of the amide substrates. The new catalysts provide the desired products with outstanding enantioselectivities (> 98 % ee) in the presence of low loadings (< 0.5 mol %) of the catalyst. Table 3: Recovery and reuse of the catalyst. Parameter Run 1 [c] 2 [d] 3 [d] 4 [e] 5 [e]Yield (%) [a] 87 (1.32 g) 82 53 75 75 ee (%) [b] 99 99

A Scalable Synthesis of Chiral Himbert Diene Ligands for Asymmetric Catalysis

“…In the case of alkenylquinoxaline 24 , the 1‐naphthyl‐substituted Himbert dienes 11 a and 11 b gave comparable results to dienes 8 a and 8 b . Comparison of these results with the highest enantioselectivities reported previously for products 19 (90% ee [23a] ), 21 (99% ee [25f] ), 23 (99% ee [26e] ), and products similar to 25 (90−97% ee [27a,c] ) demonstrates the new chiral Himbert dienes are competitive with existing best‐in‐class chiral ligands for asymmetric Rh(I)‐catalyzed 1,4‐arylations.…”

“…These enantioselectivities are higher than those reported previously for all other processes catalyzed by either Rh(I) [6b,23] or Pd(II) [24] . With dienes 8 a and 8 b , good results were also observed in enantioselective 1,4‐additions of arylboronic acids to unsaturated amide 20 [25] using Sc(OTf) 3 as an additive, [25f] nitroalkene 22 , [26] and 2‐alkenylquinoxaline 24 , [27] which gave the corresponding products 21 , 23 , and 25 in reasonable to good yields and high enantioselectivities (93–>99% ee). In the case of alkenylquinoxaline 24 , the 1‐naphthyl‐substituted Himbert dienes 11 a and 11 b gave comparable results to dienes 8 a and 8 b .…”