Based on available information, it appears that Alaska Airlines does not currently operate scheduled flights to Puerto Rico (specifically to Luis Muñoz Marín International Airport in San Juan). Some travel-sites list flights to Puerto Rico under Alaska Airlines, but other sources (such as customer discussions) suggest the carrier has never flown there.
If you would like, I can check for recent scheduled routes to confirm.
If you would like, I can check for recent scheduled routes to confirm.