Chemistry Reference
In-Depth Information
Cl
Bpin
Cl
[Ir(OMe)COD)]
2
B
2
pin
2
, Ligand
Bpin
ICl
CH
2
Cl
2
Cl
Bpin
t
-BuOK, THF
70%
50%
Cl
Bpin
1
Cl
46
Bpin
47
O
O
BB
O
B
2
pin
2
=
Ligand =
O
N
N
Scheme 12 Synthesis of pentasubstituted corannulenes directly form corannulene [
34
,
49
,
82
]
(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)diborane (B
2
pin
2
) gave 47, which can
easily be separated from the two accompanying tetrasubstituted products. The
selective formation of 1,3,5,7,9-pentakis(Bpin)corannulene (47) in the poly-
borylation conditions is caused by low steric repulsion between any two Bpin
substituents, which does not violate the
ortho
/
peri
-prohibition, and the slow sub-
stituent redistribution process with the operation of a de-borylation/re-borylation.
Compound 47 is a new precursor for synthesis of highly substituted corannulenes
through further functionalization.
Siegel and coworkers were the first to study systematically transformations of
pentachlorocorannulene 46 [
83
]. Pentaalkylcorannulenes 45 and pentaaryl-
corannulenes 50 were accessible by Ni-catalyzed cross-coupling reactions of 46
with organoaluminum and arylzinc reagents, respectively (Scheme
13
). More
recently, iron-catalyzed Kumada coupling also gave pentaalkylcorannulene deriv-
atives 45 [
84
]. 1,3,5,7,9-Pentakis(trimethylsilylethynyl)corannulene 49 (R
SiMe
3
)
[
83
] was prepared from the cross-coupling of pentachloride 46 with a large excess
of trimethylsilylethyne (ca. 50 equiv.) by using Eberhard's method [
85
] with a
pincer catalyst at high temperature (ca. 165
C). At that time, the product was
obtained in low yield. Later on, a modification of Nolan's procedure (Pd catalyst,
ligand IPr) [
86
] developed by the same group made these reactions more efficient
[
39
]. Pentaethynylcorannulenes 49 were obtained in 45-93% yields by the Stille
coupling reaction of 46 with trimethylalkynylstannanes (eight examples)
[
39
]. Reaction of 49 with tetracyanoethene (TCNE) yielded an electron-poor
corannulene with five cyanobuta-1,3-dienyl branches [
87
]. Using the Nolan's
procedure, the yields of pentaarylcorannulenes 50 were also improved, even
with sterically congested manisyl moieties, and the products were obtained in up
to 35% yield [
70
]. Moreover, the cross-coupling of 46 with less sterically congested
arylboronic acids using Nolan's protocols [
86
] or Fu's catalytic system [Pd(
t
-Bu)
3
,
CsF] [
88
] allow a variety of functionalized pentaarylcorannulenes 50 [
89
,
90
].
Direct nucleophilic substitution of 46 with nucleophiles makes it possible to
produce 48. The treatment of 46 with sodium arylthiolates gave 1,3,5,7,9-
pentakis(arylthio)corannulene derivatives 48 (XR
¼
SAr) [
83
,
91
]. Formation of
pentakis(diethylene glycol methyl ether)corannulene 48 (XR
¼
¼
O(C
2
H
4
O)OMe) by