Table 2.
Pyridines via the cycloisomerization-6π-electrocyclization sequence
 | ||||
|---|---|---|---|---|
| entry | diene-al/ -one | isolated yield (E/Z) | pyridine | isolated yield |
| 1 |  |
70%a) |  |
95% b) |
| 2 |  |
70%a) |  |
99% c) |
| 3 |  |
70% |  |
40% d) |
| 4 |  |
68% |  |
75% c) |
| 5 |  |
60% (5:1) |  |
85% d) |
| 6 |  |
80% (7:1) |  |
84% d) |
| 7 |  |
54% (8:1) |  |
73% d) |
| 8 |  |
70% (12:1) |  |
97% d) |
| 9 |  |
60% (2:1) |  |
85% d) |
| 10 |  |
74% |  |
85% b) |
| 11 |  |
70% |  |
87% c) |
E = CO2Me.
a)
See Ref. 7.
b)
methods:i) NH2OH·HCl, NaOAc, EtOH, 90 °C, 30 min, ii) PhCF3, microwave, 220-240 °C, 4 h.
c)
NH2OH·HCl, NaOAc, EtOH, microwave, 150 °C, 1-1.5 h
d)
NH2OH·HCl, NaOAc, EtOH, 90 °C, 5-24 h.