Star Alliance partners have San Francisco SFO to Copenhagen, Denmark CPH as low as $394 round trip on United.com and $405 on Swiss Airlines through their own websites for travel in April-May 2017. Fares drop again in August with low fare dates through January 2018. The price drops to $380 round trip for United tickets in fall 2017.
Momondo.com has even lower fares, as low as $335 round trip for August departures flying Star Alliance airlines.
United Airlines San Francisco SFO – Los Angeles LAX – Toronto YYZ – Copenhagen CPH – Toronto YYZ – Denver DEN – SFO
Swiss Airlines San Francisco SFO – Zurich ZRH – Copenhagen CPH – Zurich ZRH – San Francisco SFO
Summer fare $335 round trip
Momondo.com searches pull up fares as low as $335 round trip for August departures.
TravelMerry.com Air Canada/Brussels Airlines/United flights
San Francisco SFO – Toronto YYZ – Copenhagen CPH – Brussels BRU – Washington IAD – SFO