When approaching the tonic chord, from either the dominant or submediant degrees of a scale, many styles of music use a chromatic progression. This concept essentially creates a chord on each chromatic degree of the ascent. As you can see, in a minor key, the notes are simply a combination of the ascending and descending forms of the melodic minor scale.
For this reason, this type of chromatic progression would typically be found in a minor key.
Looking at the above example, we can see that all of the chromatic notes between the dominant (E) and the tonic (A) have a semitone relationship to the note preceding and to the note following. They can all, therefore, theoretically support either diatonic or secondary chords which will temporarily tonicise the note which follows. Despite this possibility, composers faced with our A minor example, would tend to use the notes E, F sharp and G sharp as the leading notes to tonicise the notes F, G and A. This is because the chords built on F, G and A are diatonic to A minor and maintain the sound of that key, whereas, tonicising the notes F sharp and G sharp require accidentals which suggest keys which are remote to A minor, and the progression would also require extra chords to achieve these remote tonicisations.
It should be noted that, because E is the dominant of A minor, any secondary chord built on E would need to occur after the dominant has sounded; not instead of the dominant.
The notes E, F sharp and G sharp may be harmonised in several ways: as roots of diminished seventh chords – the E and F sharp diminished sevenths are secondary chords while the G sharp diminished seventh is diatonic –
as the third of dominant seventh chords and their extensions – here, the C and D dominant sevenths are secondary chords while the E dominant seventh is diatonic –
also, the F major and G major chords may be preceded by half diminished seventh chords,
and finally, the progression may be harmonised using a combination of these chords.