Here is how to build, run, and debug your .NET Framework Web Application with msbuild, iisexpress, and VS Code.

From PowerShell, build your app with a portable Program Database (PDB) output. 

msbuild `
  /property:Configuration=Debug `
  /property:Platform=x64 `
  /property:DebugType=portable `
  /t:Clean,Build `
  /p:DeployOnBuild=true `
  /p:WebPublishMethod=Package `
  /p:PackageAsSingleFile=false `
  C:\dev\MyApp

From PowerShell, start your web application with IIS Express. 

appcmd add site `
  /name:"MyApp" `
  /bindings:https/*:1234:localhost `
  /physicalPath:"C:\dev\MyApp\obj\x64\Debug\Package\PackageTmp"

iisexpress MyApp

In VSCode, Create ./.vscode/launch.config with this content.

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": ".NET Attach",
      "type": "clr",
      "request": "attach",
      "processId": "${command:pickProcess}"
    }
  ]
}

In VSCode, use <CTRL> + <SHIFT> + <P> to enter the command palette and choose Start Debugging. Then attach to iisexpress.exe for your particular app.

Now you will hit breakpoints in your web application.