1. He refused to accept his suggestion.
2. He refused his suggestion.
[Both are grammatical, aren't they?]
3. He rejected to accept his suggestion.
4. H rejected accepting his suggestion.
5. He rejected his suggestion.
[Which one is gramatical among the three? Can't we use #3 or #4?]
Yes, both 1 and 2 are correct.
3 and 4 are incorrect, but 5 is correct.