Table 4 Effect of different LAs in Cu(I)-catalysed addition of EtMgBr to 1a

From: Highly enantioselective catalytic synthesis of chiral pyridines

Entry LA T (°C) Cu/L1 (%) Conv. (%)a Yield (%)b ee (%)c
1 BF3·OEt2 −78 10 0 NA NA
2 BF3·OEt2 −78 0 NA NA
3 TMSOTf −78 10 100 94 93
4 TMSOTf −78 100 (in 4 h) ND Rac
5 TMSCl −78 0 NA NA
6 TMSBr −78 0 NA NA
7 TMSCl −78 10 60 47 >99.9
8 TMSBr −78 10 100 73 >99.9
9 TESOTf −78 10 95 85 88
10 TBSOTf −78 10 87 75 77
11 TBDPSOTf −78 10 96 47 62
12 TBDPSOTf −78 40 ND Rac
13 TBSCl, TBDPSCl, TBDMSCl (−78)–0 10–25 0 NA NA
14 TESCl 0 10 40 ND 82
15 TESCl 0 0 NA NA
16 TMSCl 0 10 91 ND 91