Fig. 2: Formation of spirocycle and synthesis of iterative monomer 6.
From: A spirocyclic backbone accesses new conformational space in an extended, dipole-stabilized foldamer
a 1 (1 equiv.), 2 (1.2 equiv.), Cs2CO3 (1.5 equiv.), NBu4Br (0.1 equiv.), PhMe:CHCl3 (9:1, v:v), rt, 48 h, 70% yield, 3.6:1 d.r.; b TFA:CH2Cl2 (1:1, v:v), rt, 24 h, 91% yield; c EDCI (1.1 equiv.), NMM (2.2 equiv.), CH2Cl2, rt, 24 h, 75% yield, 11:1 d.r.; d 2,5-dibromopyrazine (5 equiv.), Pd2(dba)3 (10 mol%), Xantphos (30 mol%), Cs2CO3 (2.5 equiv.), PhMe, 110 °C, 18 h, 77% yield, >30:1 d.r. The d.r. increases throughout the sequence due to partial separation during purification. TFA trifluoroacetic acid, EDCI 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide; NMM N-methymorpholine.
