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. 2018 Nov 27;3(11):16005–16013. doi: 10.1021/acsomega.8b02749

Table 1. Evaluation of Catalysts, Reducing Agents, and Solvents in the Catalytic Reduction of 1 into 1a.

graphic file with name ao-2018-027493_0006.jpg

entry catalysta solventa reducing agenta time (h) 1%/1a%b
1   MeOH NaBH4 18 100/0
2   THF/MeOH NaBH4 18 100/0
3c   THF LiAlH4 18 43/0
4c   THF NaH 18 47/0
5   THF/MeOH TMDS 24 100/0
6 Au/TiO2 THF/MeOH NaBH4 1 0/>99
7 Au/TiO2 THF/MeOH TMDS 1 0/>99
8 Au/TiO2 MeOH TMDS 1 0/>99
9 Ag/TiO2 THF/MeOH NaBH4 18 3/97
10 Ag/TiO2 MeOH NaBH4 18 5/95
11 Ag/HMS(10) MeOH NaBH4 18 0/>99
12 Ag/HMS(10) THF/MeOH NaBH4 1 0/>99
13d Ag/HMS(10) THF/MeOH NaBH4 1 60/40
14 Ag/HMS(10) THF/MeOH TMDS 1 100/0
15 Ag/HMS(10) THF/MeOH Et3SiH 18 100/0
16 Ag/HMS(30) THF/MeOH NaBH4 1 0/>99
17 Ag/HMS(50) THF/MeOH NaBH4 1 5/95
18 HMS THF/MeOH NaBH4 1 100/0
19e AgNO3 THF/MeOH NaBH4 1 2/98
20e AgOTf THF/MeOH NaBH4 1 7/93
a

Conditions: 20 mg of the Au/TiO2 or 10 mg of the Ag/TiO2 (ca. 0.8 mol %) or 3 mg of the Ag/HMS (ca. 1.4, 4, and 7 mol %), 0.2 mmol of 1, 0.8 mmol of the hydrosilanes or 0.4 mmol of the sodium borohydride, 1 mL of solvent mixture, at rt.

b

Relative yields of 1 and 1a at appropriate time measured by 1H NMR of the crude reduction mixture.

c

Unidentified products missing either the tert-amide or the anisole group from its structure as determined by 1H NMR in some cases.

d

Equimolar amount of the reducing agent was used.

e

All the salts were used in 20 mmol %.