Both are OK, but "in-truh-steen" is much more common. This is an example of something called "R-metathesis", where the sound "R" often moves to a different position in a word. One part of R-metathesis is that if the syllable before "r" is "uh", we will move the "r" in front of it and say "ruh". Two more words where we do this: comfortable= kumf-turr-bull temperature= temp-ruh-churr You can also see R-metathesis in the way "three" becomes thirty, third, and thirteen. Some examples of r-metathesis are nonstandard, but still very common. For many natives, pretty-->"purdy", professional-->"purrfeshuhnul", introduce-->"inturrdoos". I would recommend avoiding the pronunciations in this paragraph, but you will hear natives using them quite often.

As Michael said, both are correct. I use both, depending on the emphasis, and possibly on the sentence rhythm.

Thank you, Chris!

Thank you, Chris!

Both pronunciations are accepted in North America. New Oxford American Dictionary interesting | ˈɪnt(ə)rəstɪŋ | adjective As a related note, an unstressed middle vowel of three vowels often disappears. family => fam_ly every => ev_ry interesting => int_resting