Chemistry Reference
In-Depth Information
Scheme 18 Pd(OAc)
2
-mediated cyclization of 77a,b [
56
,
57
]
Scheme 19 Pd-catalyzed preparation of IF diones 22 and 82 [
58
]
transmetallation of the arylboronic acid to the Pd(II) catalyst is followed by a
reductive elimination to give intermediates 81a,b and generate a Pd(0) species.
Switching solvents from toluene to DMA and increasing the temperature promotes
oxidative addition of the aryl halide, C-H bond activation of the central aryl ring
and subsequent cross-coupling, and then oxidation of the alcohols to ketones gives
[1,2-
b
]IF diones 22 and 82 in 49% and 58% yield, respectively, for this complex
one-pot cascade reaction.
3.2
Indeno[1,2-
b
]fluorene-6,12-olefins
While not yet as ubiquitous as the above-mentioned diones, olefination at the 6- and
12-positions on the [1,2-
b
]IF scaffold has recently gained interest because of the
increased use of the electron-withdrawing dicyanovinylene moiety. This technique
was initially described by Gompper in 1987 when dione 22 was reacted with
2 equiv. malononitrile in the presence of TiCl
4
to form olefin 83a (Scheme
20
)
[
59
], though no yield was given.
In 2008, Marks expanded the scope of synthesizing IF olefins. Diones 67d,e and
73 were converted to their corresponding exocyclic olefins 83b,c and 84a using
the TiCl
4
method described above (Schemes
21
and
22
)[
37
]. Olefin 84c was
