Level 3 – Case 40
276
OAc
AcO
3
17
3
8
2
9
1
6
5
4 4 4 4
7 7
3
8
2
9
1
6
5
4
7 7
3
7
6
5
9
1
2
3
7
6
5
9
1
2
8
4 4
22
23
20
21
11
24
enantiomer of 3
f
8
4 4
Scheme 40.11
In Summary
The solvolysis of exo-8-deltacyclyl brosylate 2 proceeds directly to nonclassical
deltacyclyl carbocation intermediate 13, whereas the endo-isomer first forms a
classical carbocation 17, which either generates intermediate 13 or isomerizes by
alkyl migrations involving nonclassical isodeltacyclyl cation 11. The special stability of the nonclassical cations compared with their classical counterparts seems
to be the key of the process.
A Ad dd di it ti io on na al l C Co om mm me en nt ts s
This problem is based on the work by Freeman PK, Dacres JE (2002) J. Org.
Chem. 67:3742-3748.
S Su ub bj je ec ct ts s o of f R Re ev vi is si io on n
Classical and nonclassical carbocations. Anchimeric assistance. Wagner-Meerwein rearrangements.
276
OAc
AcO
3
17
3
8
2
9
1
6
5
4 4 4 4
7 7
3
8
2
9
1
6
5
4
7 7
3
7
6
5
9
1
2
3
7
6
5
9
1
2
8
4 4
22
23
20
21
11
24
enantiomer of 3
f
8
4 4
Scheme 40.11
In Summary
The solvolysis of exo-8-deltacyclyl brosylate 2 proceeds directly to nonclassical
deltacyclyl carbocation intermediate 13, whereas the endo-isomer first forms a
classical carbocation 17, which either generates intermediate 13 or isomerizes by
alkyl migrations involving nonclassical isodeltacyclyl cation 11. The special stability of the nonclassical cations compared with their classical counterparts seems
to be the key of the process.
A Ad dd di it ti io on na al l C Co om mm me en nt ts s
This problem is based on the work by Freeman PK, Dacres JE (2002) J. Org.
Chem. 67:3742-3748.
S Su ub bj je ec ct ts s o of f R Re ev vi is si io on n
Classical and nonclassical carbocations. Anchimeric assistance. Wagner-Meerwein rearrangements.