[nar_v_mtz]

Hello again!

Lately these kinds of reaction mechanisms seem harder for me. I've appended an image containing the problem, in which I've made advances but I'm stuck at one point.

I can't seem to understand how to get from point 4 to point 5. Maybe it's just one step? Or maybe several? I don't know. I know that at some point the CH2 has to be deprotonated and before, the CH has to be converted not to a substituent but to a part of the cycle.

Can anyone please offer me some guidance? I know I've made a question before, but guidance is just what its needed.

Thanks in advance.

[spirochete]

I'd say typical 1,2 alkyl shift to expand the ring to make a secondary carbocation, then E1 with weak base (probably H2O) to make alkene.