Coming from a psychology perspective, I have seen eminent authors adopt both writing approaches.
Introductions to journal articles should generally have an opening. The opening of an introduction should generally introduce the aim of the research, the importance of the research, the gap in the literature that is addressed, and the method adopted to achieve the aim. Of course, often these themes are only touched on in the opening, and emerge more completely through the course of the literature review and are also often consolidated at the end of the introduction in a section often titled "the current study".
Your question pertains to how to structure the sentences or paragraphs of the opening. The more common model I have seen used is to have a motivating introductory paragraph that relates more to importance or gap and then have a second or third paragraph that culminates in the aim of the research. However, it's also possible to do it the other way around and have a very clear opening paragraph that states exactly what the study aims to do. And then have a second paragraph that touches more on importance, gap, and context.
I have found article deconstruction to be a useful tool to develop ideas about writing structure. In particular I wrote up an article deconstruction of an introduction that used the "aim-first" approach here where the first-sentence started with "The purpose of this study was ..." . I also have more detailed notes about introductions - see particularly the discussion of the opening.