C The tetrahydrofuran derivative is obtained in all cases except with the propylene adduct (R= H) which affords butadiene derivatives (eq 3). In the case where R is H, the unfavorability of a primary carbonium ion minimizes this reaction path and permits oxygen protonation and dehydration of the butadiene to predominate.
![4-[chloro(difluoro)methyl]-5,5,5-trifluoropenta-1,3-diene Structure](https://image.chemsrc.com/caspic/109/31506-41-9.png)