Chemistry Reference
In-Depth Information
O
CO
2
Et
H
+
Fe(CO)
3
Fe(CO)
3
10.65
OEt
1
0
.
5
1
0
.
4
CO
2
Et
Br
CO
2
Et
10.66
Scheme 10.18
NC
NPhth
Cu
NPhth
1. NaBH
4
, AcOH
2. TsCl, Na
2
CO
3
ZnI
Mo(CO)
2
Mo(CO)
2
Cp
Cp
10.67
10.68
H
NHTs
NHTs
Et
3
N
NO
+
BF
4
-
Ts
Mo(CO)
2
Mo(CO)(NO)
H
Cp
Cp
10.69
10.70
10.71
Scheme 10.19
attack of the carbon nucleophile on
10.21
and delivery of hydride to ketone
10.60
from sodium borohydride
occur
trans
to the iron for steric reasons.
Trimethylene methane complexes are also susceptible to nucleophilic attack.
21
Powerful nucleophiles
attack at a methylene carbon to give anionic
3
-allyl complexes
10.64
, which may be protonated or alkylated
(Scheme 10.18).
There are diene complexes of other metals that are also electrophilic. The cationic molybdenum complex
10.67
reacts with an organocopper reagent to give the product
10.68
of C1 attack (Scheme 10.19).
22
Removal
of the phthaloyl group and tosylation gives the sulfonamide
10.69
.The
3
-allyl molybdenum complex is
not sufficiently electrophilic to undergo a second nucleophilic attack. If, however, one of the CO ligands
is replaced with a nitrosyl ligand so that the complex becomes cationic, the second attack does occur. The
product is the
cis
isomer
10.71
: both nucleophilic attacks occur
trans
to the metal.
Thismolybdenumchemistry has been employed in heterocyclic systems. An enantiomerically pure
4
-diene
molybdenum complex
10.77
was prepared from arabinose
10.72
(Scheme 10.20),
23
a sugar that is unusual
in that it is naturally available in both enantiomeric forms. The anomeric hydroxy group was exchanged for
a methoxy group and the triol was differentiated by formation of a cyclic ortho-ester
10.73
. This reaction
is selective for the pair of hydroxy groups with the
cis
-relationship. Thermolysis (200
◦
C) of the cyclic
ortho-ester
10.73
gave the alkene
10.74
, which could then be converted into the allylic bromide
10.75
,the
startingmaterial for the organometallic chemistry. Treatment of bromide
10.75
with a reactive molybdenum(0)
complex
10.76
, generated by the reaction between molybdenum hexacarbonyl and acetonitrile, gave a
3
-
allyl complex
10.77
that was converted to the desired Cp derivative
10.78
by treatment with cyclopentadienyl
