Setting a shortcut to change focus to a different section in a web app?

Let's say you have a web app with 3 sections. A left nav menu, a toolbar/settings section, and a main application area. Most of the time, the user will be engaging directly with the application, and their document's focus will be potentially somewhere deep inside of the application's "hierarchy", meaning that tabbing into/out of the application to place focus on the left nav or toolbar will be a pain.

Is adding a shortcut (and making the shortcut's keystrokes visible next to that section maybe?) to change focus to the left navigation menu or the toolbar a good idea generally? Otherwise they may have to do a lot of tabbing or use some other method of interacting with that part of the site, which we'd like to avoid. Bonus points if anyone knows how this aligns with WCAG a11y requirements.

EDIT, update with wireframes:

Let's say we've got an application with a left nav, a toolbar, and an application (the "meaty" part of the application). The application focuses on the application section first, labelled "SOME APPLICATION" in the wireframes, and has many nested sections that might make it difficult to get out of using focus. Is it appropriate to allow the user to shift focus to, let's say, the first relevant link or button in each of the sections using a shortcut? (I used some contrived examples of shortcuts for the image, but you can imagine some that may be more appropriate perhaps)