C-sharp minor
There are very few symphonies written in this key. One of them is by Joseph Martin Kraus, but he later rewrote it in C minor. Another two are Mahler's Symphony No. 5 (though only the first movement is in C-sharp minor, and the finale is actually in D major) and Prokofiev's Symphony No. 7. Shostakovich's Violin Concerto No. 2 is also in C-sharp minor.