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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
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