I can think of at least one, maybe two reason why this might be uncommon, especially in jazz: > *The **Altered Dominant** chord is enharmonic to and a different voicing of the **♭II13♯11** chord.* > - Strictly speaking, the altered dominant chord would (in C major) theoretically contain some of the notes **G, B, D, F, A♭, A♯, C♯, and E♭**. This is of course from the Altered Scale, G A♭ B♭ C♭ D♭ E♭ F, and also the fifth of the chord, D, which is usually omitted in practice anyway. The Neapolitan chord traditionally was the ♭II chord; in C major this is the notes D♭, F, and A♭. In jazz, this often becomes D♭13♯11 (a tritone substitution of the dominant, but extended), containing **D♭, F, A♭, C♭, E♭, G, and B♭.** Look how similar the two are! - G and G - A♭ and A♭ - B♭ and A♯ - C♭ and B - D♭ and C♯ - E♭ and E♭ - F and F All of the notes are enharmonic to each other! The two are identical without context when certain voicings are considered. F-A-B-E might be a G13, but it could also be a D♭ ALT voicing. To answer the original question: OP asks why (whether) ♭II is rarely used in the Circle of Fifths progression. The ii chord is always followed by a V chord; such is the nature of the progression. Try to follow a D♭ chord with a G chord, and it may end up **sounding like the chords have the same root but diffeent qualities, namely from some alteration to dominant**. This can kill the motion of the progression, and while it's not always undesirable as a sound, it's certainly different enough to be a difficult substitution to pull off. For another example of the often undesirable "same-root-different-quality", try playing A-Amaj7-A7-A6-A, then juxtapose that with A-E-A7-D. And in the case of the Neapolitan chord, the more extensions you add on, the worse the effect gets. Especially in minor, where that V chord might even contain a lot of the altered extensions present in the ♭II, and it could end up sounding like **the same chord twice**. And of course, root motion by a tritone will ruin the smooth voice-leading. There will always be a jump of a minor third in one voice (with triads only). And let's not forget that the ♭II chord is definitely an acquired taste; it would be the only chord in that progression outside of the diatonic major scale. *I can't see any really great reasons to substitute that chord for the ii; if you must not use the ii, try the II instead. it's a secondary dominant, which is also non-diatonic but at least keeps the sense of resolution towards the V.* A great example of others learning about substitution possibly for the first time and then applying it in nonidiomatic contexts (no disrespect to user xnakos) is https://music.stackexchange.com/q/48592/45266. The rest of this thread is great, but OP lists a few candidate progressions where substitution is applied but doesn't sound very smooth or functional. The important thing to remember about advanced concepts is that sometimes less is more, and that the more theoretical your music gets, the easier it gets to lose track of what sounds good. Harmony is like walking dogs, to paraphrase Jacob Collier. The more complicated, the more responsibility you have to control it, but the more potential exists to be creative and original.