called a “tosyl” group.
2) Methanesulfonates are known as “mesylates” and p-toluenesulfonates are
known as “tosylates”.
or Ms− or Ts−
The mesyl group
S
O
O
S CH 3
O
O
H 3 C
The tosyl group
or or
An alkyl mesylate
S
O
R R OR R
O
S CH 3
O
O
O
H 3 C
An alkyl tosylate
MsO TsO
11.11 MESYLATES AND TOSYLATES IN SN 2 REACTIONS
- Alkyl sulfonates are frequently used as substrates for nucleophilic substitution
reactions.
Alkyl sulfonate
(tosylate, mesylate, etc.)
Sulfonate ion
S
O
O
O
R' CH 2 R +− Nu Nu S
O
O−
O
RH 2 C + R'
(very weak base −−−
a good leaving group)
- The trifluoromethanesulfonate ion (CF 3 SO 2 O–) is one of the best of all known
leaving groups.
- Alkyl trifluoromethanesulfonates –– called alkyl triflates –– react extremely
rapidly in nucleophilic substitution reactions.
- The triflate ion is such a good leaving group that even vinylic triflatres undergo
SN1 reactions and yield vinylic cations.
