I have a brasillian friend who wants to visit the UK via lisbon in portugal. IS there a transit visa required?

No, your friend does not need a visa to enter the UK via Lisbon. Brazilians do not require visas to enter the European Union. Although the U.K. is part of the EU, they are not part of the Schengen Zone of nations. Regardless, due to British immigration law, Brazilian nationals do not need transit or tourist visas to enter the UK.