Synthetic Studies on Potent Marine Drugs: Synthesis and the Crystal Structure of 6-tert-butyl-4-phenyl-4H-chromene-2-carboxylic Acid
Table 1
Survey of conditions for the condensation of 11a with 12a a.
Entry
Catalyst
Temperature
Solvent
Time
Yield
1
5 mol% AuCl3/3AgOTf
83°C
DCE
6 h
43%
2
5 mol% AuCl3
83°C
DCE
12 h
0
3
15 mol% AgOTf
83°C
DCE
12 h
trace
4
15 mol% AgCl
83°C
DCE
12 h
0
5
10 mol% LiCl
83°C
DCE
12 h
0
6
10 mol% Mg(OTf)2
83°C
DCE
12 h
0
7
10 mol% Sc(OTf)3
83°C
DCE
12 h
trace
8
10 mol% Yb(OTf)3
83°C
DCE
12 h
trace
9
10 mol% Hf(OTf)4
83°C
DCE
12 h
4%
10
10 mol% Fe(OTf)3
83°C
DCE
12 h
8%
11
10 mol% FeCl3
83°C
DCE
12 h
5%
12
10 mol% PtCl2
83°C
DCE
12 h
0
13
10 mol% Cu(OTf)2
83°C
DCE
12 h
trace
14
10 mol% Zn(OTf)2
83°C
DCE
12 h
0
15
10 mol% Al(OTf)3
83°C
DCE
12 h
trace
16
10 mol% Bi(OTf)3
83°C
DCE
12 h
5%
17
1 mol% AuCl3/3AgOTf
83°C
DCE
12 h
13%
18
5 mol% AuCl3/3AgOTf
66°C
THF
6 h
15%
19
5 mol% AuCl3/3AgOTf
76°C
CH3CN
6 h
19%
20
5 mol% AuCl3/3AgOTf
83°C
PhCH3
6 h
39%
21
5 mol% AuCl3/3AgOTf
83°C
CH3NO2
6 h
41%
General conditions: the mixture of 11a (1.0 mmol), 12a (1.0 mmol), and catalyst (1–15 mol%) in solvent (5 mL, c = 1.0 M) was stirred at 66–83°C for 6–12 hours, cooled to room temperature, and filtered through Celite. The filtrate was added with a drop of concentrated sulfuric acid and stirred at room temperature for 0.5 hour.
