This question already has an answer here:
I wrote a paper a few months ago, which I submitted to a journal and is currently under review. My field is mathematics.
Lately I have been thinking about a few things with a colleague and we came up with a small project which uses the results of my paper. The new paper is already written, and we are planning to submit it to a journal (not the same one).
The results from my paper, while obviously original, are not unexpected, and they extend previous (published) results to more general situations. This means that, at least for experts, the results themselves should be correct, so it's not something suspicious.
Is it acceptable to submit our new paper and cite the relevant results from my previous, still under review, paper? I don't think I want to wait for acceptance since it could still take a few more months and job application time is getting closer.
EDIT: I forgot to mention that my paper is available online, both on my home page and the arXiv.
EDIT: In Citing a paper under review in 2 different conferences there is a somewhat similar situation. I think mine is different in two aspects:
1) the fields, and hence the common practices, are generally different. 2) the second paper in question is with a second coauthor. It's out of the question to consider merging both papers into one, for example.