Handbook of Functionalized Organometallics Applications in S

546
13 Manganese Organometallics for the Chemoselective Synthesis of Polyfunctional Compounds
The diastereoselectivity of the 1,2-addition of various organomanganates on
cyclic ketones has been studied [13,14]. The best results have been obtained by
using heteromanganates such as (R¢COO) 2RMnLi or (R¢COO) 2RMnMgX. The nature
of the (R¢COO) group greatly influences the selectivity of the reaction
(Scheme 13.11).
O
O
Scheme 13.11
Me(n-BuCO2) 2MnLi
Et2O, -50ºC to r.t.
88%
Me(t-BuCO2) 2MnLi
THF, -50ºC to r.t.
OH
Me
+
96 :
4
OH
Me
90% 91 :
9
Organomanganese halides and organomanganates prepared by transmetallation
from organolithium and Grignard reagents add smoothly to enantiopure acylsilanes
and aldehydes bearing a chiral center in the a-position of the carbonyl
group (Scheme 13.12). The desired alcohols are obtained with satisfactory diastereoselectivities
in good to excellent yields and the starting product is not enolized
during the reaction (no isomerization of the chiral center) [15].
O
OBn
O
O
SiMe 3
CHO
Scheme 13.12
1) RMnCl, THF
2) Bu 4NF
R= Bu
R= allyl
BuMnCl, THF
-50ºC tor.t.
OBn
R
OH
60% (syn>90%)
66% (syn>75%)
O
O
HO
Bu
76% (syn/anti= 85/15)
+
Me
OH
Me
OH