I am an A-level student going into university and I am looking for a source of organic synthesis problems and answers that is freely available on the internet. The difficulty level I am looking for is something like first year undergraduate level. Any links would be greatly appreciated.
Search for the latest IChO tests and preparatory problems. You can find quite a few interesting problems.
Janice G. Smith's textbook "Organic Chemistry", while unfortunately expensive, has a good interactive workbook online which is useful even without the companion text.
You can find it here.
I would recommend doing textbook problems e.g. those of David Klein and Clayden. In addition, it might be useful to refer to MIT open courseware's organic problems. I have included their links:
These problems might be old, but I still found them useful... As for which year to do, I don't think it matters too much