Subdirectory install with access from root

I’m attempting to run WordPress from the root while keeping it in its own subdirectory. I’ve essentially followed the procedure under “Moving a root install to its own directory” in the Codex, the only difference being that my core files were already in the subdirectory, which makes Step 6 unnecessary.

This has worked exactly as intended. Now, the /wordpress bit of the URL is stripped out and it looks to the end user as though they’re browsing https://mysite.com instead of https://mysite.com/wordpress.

Problem: I don’t want all the old links to break. If an external site linked to https://mysite.com/wordpress/2011/06/an-article-slug, they’re now going to get a 404 page. I’d much prefer that they get automatically (301-)redirected to https://mysite.com/2011/06/an-article-slug, which is the new location of the file.

I’ve tried to insert a rule into the .htaccess files [N.B. the procedure in the Codex means that there are now two .htaccess files: one in the root and one in the subdirectory] to bring about this behaviour, but it is still failing to do the redirection (and is therefore delivering 404s). Here’s the .htaccess:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /wordpress/
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /wordpress/index.php [L]

RewriteBase /
RewriteRule ^wordpress/(.*)$ /$1 [R=301,NC,L]
</IfModule>
# END WordPress

The last two lines before the end of the if statement are my attempt to get the redirection to work.