A common musical pattern is the descending chromatic bass line ($\hat{1}$ –$\hat{7}$ –♭$\hat{7}$ –$\hat{6}$ –♭$\hat{6}$ –$\hat{5}$ ). Composers harmonize descending chromatic bass lines with all manner of harmonies, including secondary chords, borrowed chords, augmented sixth chords, and rarely–used diatonic chords. Below are some examples from the past four centuries.
For the harmonization of scale degree $\hat{6}$ , remember that the concept of ♯$\left.\text{vi}^{\circ}{}\right.$ was introduced when Roman numerals in minor were introduced. The notes of the ♯$\left.\text{vi}^ø{}^{7}\right.$ chord belong to the melodic minor scale.