Handbook of Functionalized Organometallics Applications in S

548
13 Manganese Organometallics for the Chemoselective Synthesis of Polyfunctional Compounds
R2 Br
Mn + + R
CO2Et 3COR4 + Ac2O R 1
Scheme 13.15
10% ZnCl 2
AcOEt, 60ºC
α-haloester Carbonyl compound Yield (%)
BrCH 2CO 2Et HexCHO 80
BrCH2CO2Et PhCHO
89
BrCH2CO2Et HeptCOMe 86
Me Br
Me CO2Et HexCHO 81
13.4
Preparation of Ketones by Acylation of Organomanganese Reagents
13.4.1
Acylation of Organomanganese Reagents
OAc
R4 R3 R1 CO 2Et
Organomanganese bromides and iodides prepared in ether react, under mild conditions,
with a vast array of acylating agents (RCOCl, (RCO) 2O, RCO 2CO 2Et, etc.)
to give the corresponding ketones in high yields (Scheme 13.16). The acylation
reaction is highly chemoselective and numerous functional groups are tolerated
(e.g. halides, nitriles, esters, and even ketones ...) [3a].
RCOCl
Yield (%)
BuMnl +
Cl
Scheme 13.16
O
91
SPh
( ) 3
Cl
O
95
Br
( ) 10
RCOCl
Cl
O
86
Ether
-10ºC to20ºC
CN
( ) 4
Cl
O
( ) 6
97
O
Bu R
Organomanganese chlorides prepared in THF are also acylated in high yields
under mild conditions. The reaction is always very chemoselective. As an illustration,
it is possible to prepare various mono- and dichloromethylketones in spite of
the high reactivity of the chlorine atoms in the a-position of the carbonyl group
(Scheme 13.17).
O
OEt
Cl
O
R 2
( ) 6
90
O
Et