Figure 4. Direct arylation approach to (R)-5 and (R)-6.
Reagents and conditions: (a) 1.5 eq pyrazole 10, 2 eq T3P (50% in EtOAc), 4 eq TEA, 2-MeTHF, room temperature (rt), 5 h, 79%; (b) 8 mol% CataCXium A, 8 mol% Pd(OAc)2, 3 eq KOAc, 1 eq H2O, t-AmOH, reflux, 16 h; (c) 4 M HCl/EtOAc, EtOAc, rt, 56 h, 71% over two steps, chiral purification by SFC; (d) 10 eq (Boc)2O, 0.5 eq DMAP, CH2Cl2, 25 °C, 16 h, 76%; (e) 8 eq Na2S2O4, 8 eq NaHCO3, H2O/THF (1:1), 20 °C, 16 h, 58%; (f) 2 eq isoamyl nitrite, 2 eq CH2I2, CH3CN, 80 °C, 4 h, 21%.