Unformatted text preview: �Br M g __ --i.� U e ther
X Mg Br _----;.� era O-D HO v 1 1- 54 00 [��+ f)]J,
� N OTE : CH 00 _-_H_2-i�� �5 + a.lkyl shift . n n expans O n g I r ecall that c arbocations probably do not exist; this could be considered a transition state 10 ri ng ex ansion f om 1 ° p r c a bocation to 2 °, resonance r stabilized c a bocation r T he m gration directly above does N OT occur i as the cationpr oduced is notr esonance stabili ed z.
An alternative mechanism could be proposed: protonate the ring oxygen, open the ring to a 2° carbocation followed by a hydride shift to a resonance-stabilized cation, ring closure, and dehydration. o :96 r?\ � (t OH j H: 9 II:� b
- h ydride sh i ft to resonance stabilized cation 2° c a bocation r .. H+ off o ne 0, H+
on the other °
.. H-O+ �90 H . 251 ...
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- Spring '10
- Chemistry, Trigraph, Transition state, Molecule, Kenji Kawai