Build another project by prebuild event without adding reference

Not that this is the best solution, but it will definitely work for what you want to do: Put the below into your pre-build event

"$(VS100COMNTOOLS)..\IDE\devenv" "csproj location OR sln location" /Rebuild "configuration required if you have more than configuration ex: Debug|x64"

This is what worked for me:

"$(DevEnvDir)devenv" "$(SolutionDir)MySolution.sln" /Build $(configuration) /project "$(SolutionDir)MyProjectFolder\MyProject.csproj"

Here $(DevEnvDir), $(SolutionDir), and $(configuration) are Visual Studio Macros, so this command will be translated into:

"C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\Common7\IDE\devenv" "D:\Learning\MySolutionFolder\MySolutionName.sln" /Build Debug /project "D:\Learning\MySolutionFolder\MyProjectFolder\MyProject.csproj"