| 1 | 251-05-8 | Imidazo[4,5-c]pyrazole | C4H2N4 | 106.09 | | |
| 2 | 251-22-9 | Furo3,2-dthiazole | C5H3NOS | 125.15 | | |
| 3 | 251-24-1 | Furo[3,2-b]furan | C6H4O2 | 108.09 | | |
| 4 | 251-41-2 | Thieno[3,2-b]thiophene | C6H4S2 | 140.23 | 56 °C | |
| 5 | 251-42-3 | Furo[2,3-d]thiazole | C5H3NOS | 125.14842 | | |
| 6 | 251-43-4 | Thieno[2,3-d]thiazole | C5H3NS2 | 141.21 | | |
| 7 | 251-49-0 | Selenolo[3,2-b]selenophene | C6H4Se2 | 234.02 | 127.5-128 °C | |
| 8 | 251-50-3 | Imidazo[4,5-d]imidazole | C4H2N4 | 106.09 | | |
| 9 | 251-56-9 | Thiazolo[5,4-d]thiazole | C4H2N2S2 | 142.2 | 149-150 °C | |
| 10 | 251-60-5 | 3H-Pyrrolizine | C7H7N | 105.13718 | | |
| 11 | 251-75-2 | 1H-Pyrrolo[1,2-a]imidazole | C6H6N2 | 106.13 | | |
| 12 | 251-80-9 | 1H-Imidazo(1,2-b)pyrazole | C5H5N3 | 107.1133 | | |
| 13 | 251-89-8 | IMIDAZO[5,1-B]THIAZOLE | C5H4N2S | 124.16 | | |
| 14 | 251-97-8 | Imidazo[2,1-b]thiazole | C5H4N2S | 124.16 | | |