CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

eaction of OsO 4 with olefins which was shown to be accelerated by pyridine. 41a The cost
considerations, however, make the stoichiometric osmylation uneconomical. Not
surprisingly, catalytic variants of the reaction, which employ relatively inexpensive
reagents for the reoxidation of the osmium (VI) glycolate products, greatly enhance its
synthetic utility. 41b Introduction of inorganic cooxidants, such as KClO 4 or NaClO 4 or
H 2 O 2 led to diminished yields due to over-oxidation. Better results were obtained with
alkaline tert-BuOOH, 41c or N-methylmorpholine N-oxide (NMO), 41d or even better with
K 3 Fe(CN) 6 -K 2 CO 3 . 41e Initial efforts to induce enantioselectivity in the osmylation with
chiral pyridine derivatives failed due to the low affinity of these ligands for OsO 4 . 42
Consequently, quinuclidine derivatives like the acetates of cinchona alkaloids (Fig. II.1.1)
were used more efficiently due to their intrinsically higher affinity for OsO 4 . 43
Et
Et
N
N
RO
H
H
OR
OMe MeO
N
N
DHQ D DHQ
Cinchona alkaloid-based ligands
N
N
OR
OR
S
O 2
Monodentate ligands
O
N
N
H
O
Azolidine
NH
NH
Ph
Ph
O N
Nap
Pr N N
N N Pr
O
N
Ph
Ph
Diamino ligands
Alk *O
N N
OAlk*
Alk *O
N
Ph
OAlk*
N
Ph
CL
O
OAlk*
Second generation ligands
Fig. II.1.1. Chiral ligands used in ADH
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