Molecule 1.

molecule 01

Base: Furan (Rule 2. component with higher priority heteroatom)
Annex: Thiophene (thiene)
Annexed numbering: starts at the sulfur and goes towards the C. bridge.
Literature base: it begins in the oxygen and goes towards the C. bridge.
Peripheral numbering: start at oxygen to give the lowest locants to the heteroatoms. (rule 1)
Name: Thieno [3,4-b] furan

Molecule 2.

molecule 02

Base: Pirano (Rule 3. component with the largest of the rings)
Attached: Furan (furo)
Annexed numbering: starts at the sulfur and goes towards the C. bridge.
Literature base: it begins in the oxygen and goes towards the C. bridge.
Peripheral numbering: start at oxygen to give the lowest locants to the heteroatoms. (rule 1)
Name: 2H- Furo [3,2-b] pyran

Molecule 3.

molecule 03

Base: Oxazine (Rule 4. component with more heteroatoms)
Annexed: Pyridine (Pyrido)
Numbering annexed: it begins in the nitrogen and goes towards the C. bridge.
Literature base: it begins in the oxygen and goes towards the C. bridge.
Peripheral numbering: it begins in the nitrogen next to the bridgehead and continues further away from it.
Name: 5H- Pyrido [2,3-d][1,2] oxazine

Molecule 4.

molecule 04

Base: Oxazole (Rule 5. component with the greatest variety of heteroatoms)
Added: Pyrazole (Pyrazolo)
Name:
1H- Pyrazolo [4,3-d][1,3] oxazole

Molecule 5.

molecule 05

Base: Dithiazine (Rule 6. component with the highest number of heteroatoms of greatest preference)
Annexed: Thiadiazine (Thiadiazine)
Name: 4H-[1,2,3]Thiadiazine[4,5-e][1,2,4]dithiazine

Molecule 6.

molecule 06

Base: Pyridazine (1,2-diazine) (Rule 7. component that, before condensation, has the least locants for its heteroatoms)
Annexed: Pyrazine (1,4-diazine) (Pyrazino)
Name: Pyrazino[2,3-d]pyridazine

Molecule 7.

molecule 07

Base: 1,2,3-Oxathiazole (Rule 8. Rule 7 considering the priority of heteroatoms)
Annex: 1,2,3-Oxazathiazole (1,2,3-Oxazathiazole)
Name: 3H,5H-[1,2,3]Oxazathiazolo[4,5-d][1,2,3]oxathiazole

Molecule 8.

molecule 08

Base: 1,3-thiazole (Rule 5. component with the greatest variety of heteroatoms)
Addendum: Imidazole (Imidazolo)
Name: 5-Methylimidazolo[2,1-b][1,3]thiazole
Note: Note that the outer numbering includes the bridging atom when it is a heteroatom .