1. He is going to leave for New York.

2. He is goin' to leave for New York.
3. He is gonna leave for New York.

4. I want to go back home.
5. I wanna go back home.
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Can we use all these expressions?

1 answer

One and four are correct. The others are all slangy and not correct grammar, although some people might use "goin'" and "gonna" in casual, informal speech.