Hey there,
Welcome to the forum and congratulations on your first post being an interesting one! So let me break my response up into two parts:
Recommendations: the obvious question is, if you leave, will your supervisors be upset? If not, then you're set! Tell them your plans, ask for their support, and if they're already table pounders, you have yourself a couple of recommenders! However, if you're going to burn bridges by leaving the company, then let's talk. A little introspection and talking it out with someone can provide a whole new list of options that you may not have considered. So answer that question first - and then we'll see how to proceed!
Start-up: Ok, so maybe the start-up isn't going to be the next Facebook overnight but clearly you believe in it enough to leave your job for it! Even if it fails, it's important experience to have and I think you're selling yourself a little short. Obviously, if you're successful, that helps
So here's another question for you to tie the above two threads into one. What's your overarching timeline here? Are you applying R1 and leaving the company at the same time? Or are you leaving now, then doing R1? Or considering leave after R1 is back?
Hmm, so it seems I have asked you more questions than I have provided answers but if you could share a little bit more, that'll help us get to the bottom of this!
Bhavik