From Rachmaninoff's 3rd piano concerto 1st movement 2nd subject:
I've been trying to understand what's going on structurally in this passage but I'm having trouble figuring out what's going on. In the picture I've presented my chord analysis. In particular I don't understand what he's doing in the red section of the image. What I'm thinking is he's just treating D as borrowed "extension" of I(63) and then walking down to ii and then slowly back to V? Can anyone help me understand what's going on here?