Is there a particular sound change that would explain changing a word-initial [ʒu] (or alternatively [dʒu]) to [iʒ] before a stressed syllable? Or might this be best explained as dropping the [u] by syncope and adding a [i] by prothesis?
I found this in a couple words of the São Vicente dialect of Cape Verdean Creole, which is related to both Portuguese and other dialects of Cape Verdean Creole:
| Portuguese | Sotavento Creoles | São Vicente |
|-------------------|-------------------|-------------|
| jogar [ʒug'aɾ] | ['dʒugɐ] | [iʒ'ga] |
| ajudar [ɐʒudˈaɾ] | ['dʒudɐ] | [iʒ'da] |
This dialect often elides unstressed [i] and [u] sounds in words, compared to other dialects or languages. So a change from [ʒu-] → [ʒ-] (or [dʒu-] → [ʒu-] → [ʒ-]) would make some sense. In other languages I'm familiar with, [ʒda] or [ʒga] would be seen as "unpronounceable", so adding an initial vowel could make sense.
However, this particular dialect elided many (most?) of the initial unstressed vowels present in Portuguese. Many words start with [ʃt-], [ʃk-], [ʃp-], etc. The dialect seems very comfortable with consonant clusters at the start of words: commonly-used words include [tʃga], [pʰta], [fka], and [zbi]. There are other cases of vowel prothesis, however.
Is there another sound change I should be looking at for a possible explanation? Or is ([dʒu-] →) [ʒu-] → [ʒ-] → [iʒ-] the best bet?
(I started to wonder more about this when I heard a speaker of this dialect pronounce a name [iʃ'sɛ] instead of the standard [ʒu'zɛ]. This speaker has both speech and hearing disorders, so isn't representative of all speakers, but the sound change was so similar that I wondered if this is a pattern seen in other languages.)
A couple notes about other prothetic vowels from @KennyLau's questions:
Words that come from Portuguese words starting with "es" plus a consonant generally have no initial vowel (as is common in Portugal), across the dialects of Cape Verdean Creole.
| Portuguese | Sotavento Creoles | São Vicente |
|------------|-------------------|-------------|
| escola | ['skɔlɐ] | ['ʃkɔlɐ] |
Another example of vowel prothesis in the São Vicente dialect is the addition of an initial /a/ in certain words:
| European Portuguese | Sotavento Creoles | São Vicente |
|---------------------|-------------------|-------------|
| mulher [muʎˈɛɾ] | [mu'dʒɛɾ] | [am'dʒɛʀ] |
| melhor [mɘʎˈɔɾ] | [mi'dʒoɾ] | [am'dʒoʀ] |
However, this might not be consistent for all speakers of the São Vicente dialect, as Wikipedia seems to say that these start with a syllabic m, instead of [am].