[Seks]

How are you supposed to remember the reagents that are involved in synthesis of compounds?

There are so many of them

[Rabn]

You should not remember specific reagents, you should remember the properties of the reagents.  I.e. an acid that is a proton donor but poor nucleophile, solvent is aqueous, need divalent metal cation, and an alkane with a primary halogen.  Doing that will allow you to not be confused if you see HBr instead of HCl, both of which may be exchanged in some synthesis.