Gene Wolfe’s “Book of the New Sun” tetralogy is said to be rife with alchemical symbolism. I have not read it yet, although it has been on my to-read stack for years. Nonetheless, here is a diagram for you, partly because it’s an easy post, but also for me, so that I can add interesting links as I might find them.
The Shadow of the Torturer
The Claw of the Conciliator
The Sword of the Lictor
The Citadel of the Autarch
Of course, there are a few other tetralogies that exist, although they are not as common as trilogies. One already mentioned on this blog is the Aeygpt Tetralogy by John Crowley.