Welcome to Autodesk Forums!

Hi,
Do you mean VIEWBASE command? If so - than it is not available in AutoCAD for Mac.

Do you need real flat 2D objects from 3D objects? - Than use FLATSHOT command.
You can also use SECTIONPLANE command to create Section object, than create 2D section using this Section object.

You can also use old SOLVIEW and SOLDRAW commands to create 2D objects from 3D geometry inside viewports in layout.

Maxim