Kinetic Resolutions - The Stoltz Group

t-Bu
R 3
OH
R 1
R 1
R 1
(±)- + +
R 2
N N
Mn
MeO O Cl O
OMe
t-Bu
Epoxidation of Allylic Alcohols - Salen too! (Adam)
(R,R)-10
10 mol% Catalyst 10 or 11
t-Bu
20 mol% PPNO
60 mol% PhIO
CH 2Cl 2, r.t.
Enantiomer of alcohol depends on catalyst used (10 and 11 give opposite enantioenrichment)
Epoxide ee's 50-80%, Alcohol ee's < 50% (10 -50% conv.), s = 1.5-12.9
Oxidation of alcohol to ketone over epoxidation often problematic
R 3
OH
R 2
N N
Mn
O
R 3
OH
R 2
t-Bu O Cl O
t-Bu
t-Bu
(S,S)-11
t-Bu
R 3
O
R 2
PPNO
R 1
N O
Adam, et. al., J. Org. Chem., 2001, 66, 5796
Selectivity in Salen Epoxidations of Allylic Alcohols
O
t-Bu
N
O
Mn
2
N
HO
O
t-Bu
Ph
3
1 - A 1,3 Interaction
1
2 - Hydrogen Bonding
3 - Katsuki Trajectory
H
Me
t-Bu
Me
Ph
H
OH
Katsuki Trajectory
O
Mn
O
R L is forced away from the bulky salen tert-butyl groups, especially when R L is aromatic
1, 2, and 3 require that the (S)-enantiomer be the more reactive (when the catalyst is derived from the (S,S)-salen
ligand, as shown)
N
R S
R L
Adam, et. al., J. Org. Chem., 2001, 66, 5796
Katsuki, et. al., J. Mol. Cat. A, 1996, 113, 87
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