Dejan Lekic had put hosts Osasuna ahead five minutes before the break in Pamplona before Sanchez headed in a 48th-minute equaliser for the Catalans.
Substitute Lionel Messi set up Roberto to seal victory after 71 minutes for a 6-1 aggregate scoreline and a meeting with Real Madrid next Wednesday.
Real Madrid qualified with a 72nd minute goal from Karim Benzema on Tuesday giving them a 1-0 win over Malaga for a 4-2 aggregate victory.
Real Madrid host Barcelona in the first leg next Wednesday with the return leg on January 25 at the Camp Nou. The two sides meet again just a month after the 'clasico' which Barcelona won 3-1 at the Santiago Bernabeu.
Athletic Bilbao also progressed with a 4-0 win over third division Albacete on Thursday.
Goals from Markel Susaeta (24), Ander Herrero (64), Gaizka Toquero (77) amd Mikel San Jose (86) ensured Athletic will play Real Mallorca in the last eight.
Valencia take on Levante and giant-killing Mirandes face Espanyol.