Table 1. Photocyclization of Alkyl 1,2-Diketone 1 in Solution and Crystalline Statea.
| entry | medium | T (°C) | t (h) | 2/3/4b | (%)c |
|---|---|---|---|---|---|
| 1 | C6H6d | r.t. | 3 | 72/22/6 | 92 |
| 2 | C6D6 | 25 | 3 | 74/19/7 | 88 |
| 3 | CDCl3 | 25 | 2 | 78/20/2 | 81 |
| 4 | CDCl3 | –60 | 4 | 69/21/10 | 79 |
| 5 | CH3CN | 25 | 3.5 | 69/25/6 | 81 |
| 6 | tBuOH | 30 | 3.5 | 75/21/4 | 82 |
| 7 | Et2O | 25 | 2.5 | 77/17/4 | 83 |
| 8 | Et2O | –40 | 4.5 | 80/15/5 | 81 |
| 9 | Et2O | –90 | 4.5 | 83/13/4 | 84 |
| 10 | [BMIm]OTfe | 25 | 4 | 52/41/7 | 72 |
| 11 | 1A (crystals) | 25 | 9 | 0/100/0 | 92 |
| 12 | 1B (crystals) | 25 | 30 | 10/90/0 | 93 |
a
Irradiation with a Philips master PL electronic daylight lamp 23 W/865.
b
Ratio measured by 1H NMR spectroscopy.
c
Chromatographic isolated yield.
d
Irradiation with direct sunlight.
e
[BMIm]OTf: 1-butyl-3-metylimidazolium trifluoromethanesulfonate.