I have the same request!!!
I thought about creating a workflow alert to let the sales people know when there is a deal that was created without a contact and or a company, but I had the same problem, I can’t add these properties to the workflow!
There is also another idea talking about this issue: https://community.hubspot.com/t5/HubSpot-Ideas/Associated-Contact-and-Company-required-when-create-a-Deal/idc-p/274019#M35932