Chemistry Reference
In-Depth Information
Fig. 10 Convergent bond lengths in extended [N]phenylenes [
67
]
Fig. 11 Archimedene 53.
Reprinted with permission
from [
68
]. Copyright 2003
American Chemical Society
R
R
Br
OHC
CHO
steps
CpCo(CO)
2
m
-xylene, h
,
R
Br
Br
R
CHO
R
R
54a
: R = H, 2%
54b
: R = hex, 0.24%
Scheme 15 Threefold cyclotrimerization to give archimedene fragment 54 [
68
]
six- and ten-membered rings are slightly negative,
0.2 respectively,
while those of the four-membered ring are slightly positive, 3.2 indicating that the
system is neither strongly aromatic nor antiaromatic.
Synthetic attempts towards 53 have so far focused on assembling smaller
fragments. In 2003, Vollhardt and coworkers reported the synthesis of the
C
3h
-
symmetric fragment [7]phenylene 54 (highlighted in red in Fig.
10
) by a threefold
cyclotrimerization of
1.9 and
the appropriate nonayne precursor
(Scheme
15
)[
68
].
