Chemistry Reference
In-Depth Information
Tab l e 9 . 2
Substrate
Product
Yield (%)
R
R
Z
Z
O
R
′
R
′
Z
R
R
′
Me
Ph
Me
H
H
H
H
Ph
C(CO
2
Et)
2
O
NTs
O
98
98
98
93
O
+
R
R
R
Ph
n-Pent
Cl
98
98
22
although the average size of Raney cobalt seems to be in the range of nanoparticles.
19
The
catalytic system was quite effective for the intramolecular PKR of carbon-tethered enynes
(Table 9.3). However, rather moderate yields (52-56%) were observed for the intermolec-
ular reaction of norbornene with 1-pentyne, 1-octyne or 4-pentyn-1-ol. Raney cobalt is
commercially available, cheap, easy to handle and nontoxic. Moreover, the catalytic sys-
tem can be efficiently separated and reused by filtration and by exploiting its ferromagnetic
properties.
9.2.4 Mesoporous Organized Zirconium Oxide Silica Powders as Catalyst
21
The mesoporous silicas have been considered fascinating materials for many technological
applications due to their porous and morphological characteristics.
20
Sanchez et al. re-
ported
21
the use of mesoporous mixed zirconia-silica powders (
ZS20
c
) in the PKR. Under
the optimized reaction conditions (4 mol% zirconium at 130
◦
C under 30 bar of CO for 48 h
in toluene), they studied a reaction between cyclohexene and alkynes such as phenylacety-
lene, 1-octyne, 4-octyne and methyl butyndioate (Scheme 9.4). The conversion rates for
terminal alkynes were low, 20% for phenylacetylene and 12% for 1-octyne. In the cases
of 4-octyne and methyl butynedioate, no conversion was observed. One notable thing is
that the acetylenic moiety was located in
position of the carbonyl group in the reaction
product. Overall, the observed regioselectivity is rather unusual and thus interesting, but
β
