Rearrangement of Grignard reagent formed from exocycloproyl vinyl bromide
Grignard reagents are capable of rearranging, especially in this situation where there is significant strain. The specific vinyl bromide you drew here has been studied: J. Org. Chem., 1974, 39 (10), pp 1411–1416. The table of data shown below is hard to read without including more of the text, but it was found that at 66 C in THF, after 5-10 minutes, 41% of the initial Grignard had undergone rearrangement, so this is a fairly likely process.





A potential mechanism for the rearrangement is: