Level 1 – Case 5
28
O
O
SnCl 4
O
O
SnCl 4
O
OSnCl 3
O
Cl 3 SnO
Cl
Cl
O
OH
Cl
O
O
O
O
1
3
4
2
5
6
7
Scheme 5.1
and 10, which recombine to form the carbocationic intermediate. Fragments 9 and
10 could be solvent-separated fragments or a solvent-caged ion pair (path b,
r
Scheme 5.2). The investigation of the reaction mechanism was finally done by
means of labeling crossover experiments.
O
O
O
SnCl 4
O
O
Cl 4 Sn
O
OSnCl 3
Cl
1, 2
8
3, 4
9
1 0
n
n
n
n
path a
path b
Scheme 5.2
Discuss the following experiments and determine if the rearrangement proceeds
via an inter- or an intramolecular pathway
Experimental Data
E Ex E Ex E Ex Ex E E p
x xp xp xp p
x xpe er ri ri ri r ri ri r rim i im im im
i i e en nt t 1 1
Unlabeled cis-11 was treated with SnCl 4 in dichloromethane (DCM) at –30°C,
yielding exclusively trans-12 as a (3:1) mixture of diastereomers (Scheme 5.3).
28
O
O
SnCl 4
O
O
SnCl 4
O
OSnCl 3
O
Cl 3 SnO
Cl
Cl
O
OH
Cl
O
O
O
O
1
3
4
2
5
6
7
Scheme 5.1
and 10, which recombine to form the carbocationic intermediate. Fragments 9 and
10 could be solvent-separated fragments or a solvent-caged ion pair (path b,
r
Scheme 5.2). The investigation of the reaction mechanism was finally done by
means of labeling crossover experiments.
O
O
O
SnCl 4
O
O
Cl 4 Sn
O
OSnCl 3
Cl
1, 2
8
3, 4
9
1 0
n
n
n
n
path a
path b
Scheme 5.2
Discuss the following experiments and determine if the rearrangement proceeds
via an inter- or an intramolecular pathway
Experimental Data
E Ex E Ex E Ex Ex E E p
x xp xp xp p
x xpe er ri ri ri r ri ri r rim i im im im
i i e en nt t 1 1
Unlabeled cis-11 was treated with SnCl 4 in dichloromethane (DCM) at –30°C,
yielding exclusively trans-12 as a (3:1) mixture of diastereomers (Scheme 5.3).