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. 2020 May 26;15(13):1139–1149. doi: 10.1002/cmdc.202000147

Scheme 1.

Scheme 1

A) The reported synthesis of C‐3 aminoalkyl‐substituted 2,4‐PDCA derivative 18 31 compared with B) the new route to C‐3 aminoalkyl‐substituted 2,4‐PDCA derivatives. a) Br2, 20 % oleum, 165 °C, 35 %; b) KMnO4, NaOH, H2O, reflux; c) H2SO4, MeOH, reflux, 45 % (2 steps); d) amine (1.2 equiv), Pd2(dba)3 (2 mol%), Xantphos (6 mol%), Cs2CO3, toluene, 110 °C, 69 %; e) NaOH, MeOH/H2O, then: HCl, 96 %; f) SOCl2, MeOH, reflux, 89 %; g) CO (1.5 atm), Cl2Pd‐rac‐BINAP (1 mol%), iPr2NEt, MeOH, 100 °C (sand bath temperature, sealed flask), 90 %; h) alkylamine (H2NR′, 1.5 equiv), Pd(OAc)2 (4 mol%), Xantphos (6 mol%), pyridine, toluene, 190 °C (sand bath temperature, sealed flask), 32–71 %; i) LiOH, MeOH/H2O, 0 °C to RT, then: Dowex® 50XW8, 61–88 %. Crystal structure colour code: grey: carbons; white: hydrogens; blue: nitrogen; red: oxygens; green: chlorine.