Q Re: Sound Change (On Glide)

Now, I've never actually been taught this in any linguistics class (hence, why I'm
asking), but in Spanish, it appears that Latin long mid vowels, when stressed,
became diphthongs with an on-glide. Examples:

sentar "to sit" (stress on the /a/)

nosotros sentamos "we sit" (stress on the /a/)
yo siento "I sit" (stress on the /e/)

dormir "to sleep" (stress on the /i/)

nosotros dormimos "we sleep" (stress on the/i/)
yo duermo "I sleep" (stress on the /e/)

Note: I'm imagining that there was an secondary stage with "dormir" where it was
actually /dwormo/, at one time, and then the vowel fronted, for reasons
unknown.

My question: Does anyone have any examples of this happening in other languages
(nat or non)? I don't believe I've ever seen another example of this (though
I've seen countless where obstruents become palatalized before front vowels and
labialized before back vowels, resulting *kind of* in diphthongs with
on-glides), so I was wondering how it worked, and if it could work another way.

-David

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