Skip to main content
. Author manuscript; available in PMC: 2019 Apr 3.
Published in final edited form as: Org Lett. 2019 Jan 30;21(4):876–879. doi: 10.1021/acs.orglett.8b03716

Table 1.

Selective Boc-protection of 4.a

graphic file with name nihms-1008789-t0008.jpg
Entry MLx Time (h) Selectivity (7 : 8)c Yield for 7 (%)d
1 CuSO4 12 1 : 0 20
2 Cu(OAc)2 12(1)b 1 : 0 95
3 CuBr2 12 1 : 0 10
4 CuCl2 12(5)b,e 1 : 0 90
5 NiCl2•6H2O 12(5)b >19 : 1 85
6 Ni(OAc)2•nH2O 12(5)b >19 : 1 85
7 Ni(NO3)2•6H2O 12(5)b >19 : 1 85
8 VCl3 12 4 : 1 40
9 Zn(NO3)2•6H2O 12(3)b 1 : 1 45
10 ZnCl2 12(3)b 1 : 1 40
11 CoCl2 12(3)b 1 : 1 45
12 FeSO4•H2O 12(3)b 1 : 1 40
13 FeCl3•6H2O 12(3)b 1 : 1 40
14 - 12(1)b 1 : 1 35
a

Reaction condition: 3 (1.0 equiv), MLx (3.0 equiv), and NaOH (1N, 4.0 equiv) in DMF-MeOH-H2O (1/1/1, 0.05M), after 30 min. (Boc)2O (2.5 equiv)

b

time in the parenthesis: time required for the reaction to be completed

c

Selectivity was determined via HPLC analysis for the reaction mixtures after 12h

d

Isolated yield

e

the same reaction with CuCl2 (1.0 equiv) provided 6 in >90 yield in 1 h.