[rolnor]

I am checking in Scifinder if my compounds have been synthezised before, how big risk is it that I am missing something? Does Reaxys cover more?

[kriggy]

IIRC now they cover pretty much same stuff but one of them (reaxys I think) is few years older so it makes a difference in the older literature. Also, I had some troubles with this when scifinder didnt find my compound and reaxys did but those were quite rare. Novadays when Im looking for a procedure to make something, I only look at reaxys.

[EngPet]

SciFinder covers more, but reaxys has the power to retrieve more old literature, so they are complementary and you should check both of them for more assurance.