Abstract
The asymmetric cross-coupling reaction is developed as a straightforward strategy toward 1,1-diaryl alkanes, which are a key skeleton in a series of natural products and bioactive molecules in recent years. Here we report an enantioselective benzylic C(sp3)−H bond arylation via photoredox/nickel dual catalysis. Sterically hindered chiral biimidazoline ligands are designed for this asymmetric cross-coupling reaction. Readily available alkyl benzenes and aryl bromides with various functional groups tolerance can be easily and directly transferred to useful chiral 1,1-diaryl alkanes including pharmaceutical intermediates and bioactive molecules. This reaction proceeds smoothly under mild conditions without the use of external redox reagents.
Highlights
The asymmetric cross-coupling reaction is developed as a straightforward strategy toward 1,1-diaryl alkanes, which are a key skeleton in a series of natural products and bioactive molecules in recent years
By the merge of photocatalysis and transition-metal catalysis[20,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56], the milestone of C–H arylation reactions via hydrogen atom transfer (HAT) process has been recently marked by Molander and colleagues[57], Shields and Doyle[58], MacMillan and colleagues[59], and Martin and colleagues[60] (Fig. 1b) to provide an alternative for the direct construction of 1,1-diaryl alkanes with readily available starting materials in a mild reaction condition
Inspired by previous reports on nickelcatalyzed asymmetric cross-coupling reactions using chiral BiOX ligand, we were so excited to find that the chiral BiOX ligands LS1 could accelerate the reaction to deliver 3aa in 79% yield, with a moderate enantiomeric ratio (69:31 er) (Table 1, entry 1)
Summary
The asymmetric cross-coupling reaction is developed as a straightforward strategy toward 1,1-diaryl alkanes, which are a key skeleton in a series of natural products and bioactive molecules in recent years. Available alkyl benzenes and aryl bromides with various functional groups tolerance can be and directly transferred to useful chiral 1,1-diaryl alkanes including pharmaceutical intermediates and bioactive molecules This reaction proceeds smoothly under mild conditions without the use of external redox reagents. We report the enantioselective benzylic C–H arylation of readily available alkyl benzene with commercially available aryl bromides by using our designed chiral biimidazoline (BiIM) ligand (Fig. 1c). This protocol is redox neutral without using any additional single-electron oxidant or reductant
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