Table 1. Compound Numbering Scheme and Isolated Yields (%) of Heterocycles.
| R′
of nitrone/reaction conditions |
||||
|---|---|---|---|---|
| R2 of NCNR2 | Me | reaction conditions | CH2Ph | reaction conditions |
| Me2 | 1 (68) | 2 h, 45 °C | 2 (30) | 2 h, 45 °C |
| Et2 | 3 (30) | 2 h, 45 °C | 4 tracesa | |
| (CH2)5 | 5 (60) | 2 h, 45 °C | 6 (50) | 2 h, 45 °C |
| (CH2)4O | 7 (73) | 2 h, 45 °C | 8 (55) | 2 h, 45 °C |
| (CH2)4 | 9 (57) | 2 h, 45 °C | 10 (34) | 2 h, 45 °C |
| tetrahydroisoquinolin-2-yl (C9H10) | 11 (45) | reaction time 24 h, RT | 12 (28) | reaction time 24 h, RT |
| (CH2Ph)2 | 13 (68) | 2 h, 45 °C | 14 (53) | 24 h, 45 °C |
| Ph(Me) | 15 (45) | 2 h, 45 °C | 16 (50) | 48 h, 45 °C |
a
We were unable to isolate the cycloadduct when the reaction was carried out under standard conditions (2 h, 45 °C); upon prolonged treatment (24 h, 45 °C) under harsh conditions (MW irradiation, 100 °C, 30 min), we only observed peaks corresponding to the cycloadduct in HRESI+-MS of the reaction mixture.