Chemistry Reference
In-Depth Information
Based on these results, a catalytic process was developed and the reaction of several
allyl acetates with the same cyclic nucleophile or sodium malonate was investigated in
the presence of several Mo complexes. While Mo(dppe)(CO)
4
and Mo(TMEDA)(CO)
4
were nearly ineffective, Mo(CO)
6
and Mo(bipy)(CO)
4
gave the expected allylation
product in good yields, although the reactions, especially of the bipy complex, were
rather slow. In general, 5-20 mol % of catalyst had to be used and the reactions had to
be carried out in refl uxing toluene to get acceptable yields. These are much harsher
conditions compared with Pd-catalyzed reactions. Interestingly, the regioselectivity
observed with these two Mo catalysts was opposite (Scheme 8B.52).
Ph
ONa
O
O
CO
2
Me
Ph
CO
2
Me
Ph
OAc
CO
2
Me
+
Mo-Cat.,
toluene,
Δ
Mo(CO)
6
95
:
5
(73%)
Toluene,
Δ
Mo(bipy)(CO)
4
30
:
70
(75%)
CO
2
Me
OAc
CO
2
Me
CO
2
Me
NaCH(COOMe)
2
+
CO
2
Me
Mo-Cat.,
toluene,
Δ
Mo(CO)
6
Mo(bipy)(CO)
4
15
:
85
(69%)
67
:
33
(45%)
ONa
O
O
CO
2
Me
CO
2
Me
CO
2
Me
OAc
+
Mo(CO)
6,
solvent
95
:
5
Toluene
DME
15
:
85
Scheme 8B.52.
Catalytic Mo - catalyzed allylic alkylations.
The solvent has also a marked effect on the reaction in terms of rate and regioselec-
tivity. Etheral solvents such as THF or dioxane decellerate the reaction relative to
toluene, presumably due to their coordination ability for the metal, thereby reducing its
electrophilicity. For example, the reaction of crotyl acetate in DME is not only slower
than in toluene, but also shows a different regioselectivity (Scheme 8B.52). This effect
can be explained by the formation of a new catalyst, that is, Mo(DME)(CO)
4
. DME as
a strong σ-donor ligand, comparable to bipy, therefore shows a similar selectivity pattern.
