Synthesis and reactivity of 5,10,15-triaryl doubly N-confused bilanes

Article abstract of DOI:10.1002/chem.201103034

A series of 5,10,15-tris(pentafluorophenyl) doubly N-confused bilanes were synthesized in a stepwise manner with the aid of sterically demanding N-protecting groups, in which the difference in reactivity between regular pyrrole and N-confused pyrrole plays a crucial role in the synthetic strategy. Some doubly N-confused bilanes were converted into porphyrinoids or a unique 2:2 copper(II) complex with a helical structure. In addition, the conformations and electronic states of the doubly N-confused bilanes were investigated theoretically, giving fruitful information about the effect of confusion on the bilane skeleton.

Full text of DOI:10.1002/chem.201103034

DOI: 10.1002/chem.201103034
Synthesis and Reactivity of 5,10,15-Triaryl Doubly N-Confused Bilanes
Motoki Toganoh,[a] Sabapathi Gokulnath,[a] Yasunori Kawabe,[a] and
Hiroyuki Furuta*[a, b]
Abstract: A series of 5,10,15-tris(penta-
fluorophenyl) doubly N-confused bi-
lanes were synthesized in a stepwise
manner with the aid of sterically de-
manding N-protecting groups, in which
the difference in reactivity between
regular pyrrole and N-confused pyrrole
plays a crucial role in the synthetic
strategy. Some doubly N-confused bi-
lanes were converted into porphyri-
noids or a unique 2:2 copper(II) com-
plex with a helical structure. In addi-
tion, the conformations and electronic
states of the doubly N-confused bilanes
were investigated theoretically, giving
fruitful information about the effect of
confusion on the bilane skeleton.
Keywords: bilanes · confused com-
pounds
· macrocycles · porphy-
AHCTUNGTREGrNNNU inoids · pyrroles
Introduction
During the course of these studies, it became important to
prepare multiply N-confused oligopyrroles because they
were requisite compounds for the construction of multiply
N-confused porphyrinoids.[9] Despite rich examples of N-
confused porphyrinoids, the study of N-confused oligopyr-
roles is still in its infancy.[10]
Bilane is composed of four pyrrole units and three methyl-
ene carbon atoms, forming a linear precursor for porphyrin
and vitamin B12 in biosynthesis.[1] Although bilanes contain-
ing three identical substituents on the methylene carbon
atoms are obtained directly in an acid-catalyzed condensa-
tion reaction of pyrrole and aldehyde,[2] the yields are usual-
ly low, and thus, stepwise construction would be suitable for
efficient preparation. The stepwise method is essential for
the synthesis of asymmetrically meso-[3] and b-substituted bi-
lanes.[4] The bilanes thus synthesized are important precur-
sors for corroles and asymmetrically substituted porphy-
ACHTUNGTRENNUNG
and related macrocycles. Due to the high reactivity of a-
carbon atoms, pyrrole rings are usually connected to me-
thine or meso-carbon atoms in an a,a’-fashion.[5] Meanwhile,
we have managed to connect pyrrole rings in an a,b’-fashion
to the meso-carbon atoms, giving a wide variety of N-con-
fused porphyrinoids.[6] One important feature of N-confused
porphyrinoids is the high reactivity of the N-confused pyr-
role ring.[7] In particular, unique intramolecular fusion reac-
tions of N-confused porphyrinoids offer a way to peculiar
fused porphyrinoids.[8]
The significance of the study on confusion is categorized
into two elements. One is the creation of new molecules
with unique structures and interesting properties. Another is
the systematic study of the isomers of porphyrins and relat-
ed oligopyrrolic compounds. There is no doubt that under-
standing of the effects of conformation, polarization, hydro-
gen bonding, and so forth is important for the development
of porphyrin chemistry. However, it is often difficult to elu-
cidate them only with a single compound or regular oligo-
pyrrolic compound. The concept of confusion enables us to
create a library of compounds with similar structures and
properties. A comparison of regular and confused oligopyr-
rolic compounds would provide much information about
those effects.
[a] Dr. M. Toganoh, Dr. S. Gokulnath, Y. Kawabe, Prof. Dr. H. Furuta
Department of Chemistry and Biochemistry
Graduate School of Engineering, Kyushu University (Japan)
[b] Prof. Dr. H. Furuta
International Research Center for Molecular Systems
Kyushu University, 744 Moto-oka
Nishi-ku, Fukuoka 819-0395 (Japan)
Fax : (+81)92-802-2865
E-mail: hfuruta@cstf.kyushu-u.ac.jp
Herein, the synthesis and reactivity of a series of 5,10,15-
tris(pentafluorophenyl) doubly N-confused bilanes are re-
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201103034.
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FULL PAPER
ported in detail. The use of pentafluorophenyl groups is
very important to stabilize any intermediates. It is also bene-
ficial to avoid scrambling reactions. Although two isomers
of doubly N-confused bilanes have already been reported,
they are described again for comparison.[11]
on previously reported nomenclature for a series of porphy-
rin isomers,[9g] N, Ca, and Cb are used to indicate the site of
N confusion, as shown in the upper-left corner of Scheme 1.
First, oligopyrrole is arranged in a circular pattern, in which
a vacant site is placed downward. Second, each pyrrole ring
is assigned as rings A, B, and so on in a clockwise manner
starting from the lower left ring. N-Confused pyrrole rings
are placed in an alphabetically favorable manner. Finally,
the positions of the nitrogen atoms are indicated from rings
A to D, such as (Ca,N,N,N) and (Ca,Cb,N,N). These signs are
placed after the abbreviated names, NCB for singly N-con-
fused bilane, N2CB for doubly N-confused bilane, N3CB for
triply N-confused bilane, and N4CB for quadruply N-con-
fused bilane. Isomers of NCB, N2CB, N3CB, and N4CB are
listed in Scheme 1 with trivial names. Previously, NCB-
(Ca,N,N,N) and NCB-(N,Ca,N,N) were prepared from N-
confused dipyrromethane for the synthesis of N-confused
corroles and norroles.[12] Importantly, this rule can also be
applied to higher analogues, such as penta- and hexapyr-
rane.
Results and Discussion
Nomenclature: Because many isomers exist in N-confused
bilanes, we assign trivial names to distinguish them. Based
The numbering systems for dipyrromethane, tripyrrane,
and bilane were reviewed. To retain systematic numbering,
the positions of the nitrogen atoms in regular oligopyrroles
are numbered at the end, as shown in Scheme 2. In the case
of bilane, the 20-position is vacant, according to IUPAC rec-
ommendations.[13] Starting from regular oligopyrroles, nitro-
gen atoms are replaced with carbon atoms and the positions
are indicated by “carba”. Similarly, the carbon atoms are re-
placed with nitrogen atoms and then the positions are indi-
cated by “aza”. Specific examples of N-confused oligopyr-
roles are also shown in Scheme 2 with their compound
names.
Scheme 2. Numbering systems for oligopyrroles.
General strategy: The introduction of N-confused pyrrole
rings relied on steric repulsion imposed by an N-protecting
group of the pyrrole ring.[5] Acylation, halogenation, and
acid condensation reactions with pyrrole or dipyrromethane
usually proceed regioselectively at the a position. When
sterically demanding N-protecting groups, such as triisopro-
pylsilyl (TIPS), are introduced, reactions proceed preferen-
Scheme 1. Structures and trivial names for bilane isomers.
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H. Furuta et al.
tially at the b position.[14] With the aid of the TIPS group,
singly and doubly N-confused dipyrromethane could be pre-
pared as summarized in Scheme 3.[11,12] The b-substituted
Scheme 3. Preparation of singly and doubly N-confused dipyrromethanes.
Scheme 4. Strategy for the synthesis of N-confused oligopyrroles.
pyrrole (or N-confused pyrrole), singly N-confused dipyrro-
methane, and doubly N-confused dipyrromethane are im-
portant building blocks for the synthesis of N-confused oli-
gopyrroles. It should be noted that singly and doubly N-con-
fused dipyrromethane derivatives could be prepared without
nitrogen protection.[15] The effectiveness of TIPS protection
is illustrated by the X-ray structure of N,N’-diprotected
doubly N-confused dipyrromethane (Figure 1), in which the
Based on the findings summarized in Scheme 4, retrosyn-
thetic analysis for N2CBs was achieved (Scheme 5). Each
isomer is labeled with Roman numerals for clarity. Isomer-
Scheme 5. Retrosynthetic analysis of N2CBs.
Figure 1. X-ray structure of N,N’-protected doubly N-confused dipyrro-
methane. Thermal ellipsoids are shown at the 30% probability level.
s II and VII could be synthesized from doubly N-confused
dipyrromethane. Isomers III and VI could be prepared from
singly N-confused dipyrromethane. Isomers I and IV require
both an N-confused pyrrole derivative and singly N-con-
fused dipyrromethane. Isomer V could be synthesized
simply from an N-confused pyrrole derivative and regular
dipyrromethane. Isomer VIII might be derived from doubly
N-protected dipyrromethane, although this has not yet been
developed. In general, the synthesis of N2CBs with neigh-
boring N-confused pyrrole rings is troublesome, except
when doubly N-confused dipyrromethane is chosen as a
starting precursor.
a positions of pyrrole rings are blocked by isopropyl groups.
The difference in reactivity between regular pyrrole and
N-confused pyrrole is an important factor for the synthesis
of N-confused oligopyrroles (Scheme 4). In acid condensa-
tion reactions, regular pyrrole usually shows a higher reac-
tivity than that of N-confused pyrrole.[9f,g] Thus, it is better
to avoid acid condensation for the synthesis of N-confused
pyrrole in the presence of a-free regular pyrroles. The use
of intact pyrrole is most favorable because excess amounts
can be used readily. In the case of acylation reactions, regu-
lar pyrrole and N-confused pyrrole behave in a similar
Synthesis of N2CB-(Ca,Ca,N,N) (isomer I): The synthesis of
isomer I required the reaction of N-confused pyrrole deriva-
tive 2 with singly N-confused dipyrromethane 1 (Scheme 6).
Because acid condensation for the synthesis of the N-con-
fused pyrrole ring is unfavorable, the a’ position of the regu-
lar pyrrole moiety in 1 was blocked by the acyl group to fa-
cilitate reaction at the N-confused pyrrole moiety. Treat-
manner.[12] Nevertheless, N-confused pyrrole showed
a
higher reactivity than that of regular pyrrole for limited sub-
strates (e.g., Scheme 15 below). To date, site-selective acyla-
tion in a reproducible fashion has been difficult. Important-
ly, a mixture of acylated products could be separated by
standard silica gel column chromatography.
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5,10,15-Triaryl Doubly N-Confused Bilanes
FULL PAPER
Synthesis
of
N2CB-
(Ca,N,Cb,N) (isomer IV): A key
intermediate for the synthesis
of isomer IV was symmetrical
doubly N-confused tripyrrane
12 (Scheme 9). Acid condensa-
tion of N-protected singly N-
confused dipyrromethane
8
with 2 and subsequent depro-
tection with Bu4NF afforded 12
in 63% yield (2 steps). Acyla-
tion of 12 gave monoacyl
doubly N-confused tripyrrane
13 in 55% yield and reduction
of 13 gave the corresponding
carbinol 14 quantitatively. Fi-
nally, acid condensation of 14
with pyrrole gave isomer IV in
76% yield.
Scheme 6. Synthesis of N2CB-(Ca,Ca,N,N) (isomer I).
ment of an equimolar mixture of 1 and 2 with CF3CO2H
gave doubly N-confused tripyrrane derivative 3 in 79%
yield. Deprotection of 3 with Bu4NF gave 4 in 96% yield
and subsequent reduction with NaBH4 gave doubly N-con-
fused tripyrrane monocarbinol 5 quantitatively. Finally, acid
condensation of 5 with pyrrole afforded isomer I in 72%
yield.
Synthesis of N2CB-(Ca,Cb,N,N) (isomer II): The synthesis of
isomer II was reported previously.[11] Acid-catalyzed conden-
sation of doubly N-confused dipyrromethane monocarbinol
6 with regular dipyrromethane 7 gave isomer II in 44%
yield (Scheme 7).
Scheme 8. Synthesis of N2CB-(Ca,N,Ca,N) (isomer III).
Synthesis of N2CB-(Ca,N,N,Cb) (isomer V): Isomer V has
a symmetrical structure and can be prepared in fewer steps
(Scheme 10). The acid-catalyzed condensation reaction of
regular dipyrromethane 7 with 2 gave N-protected N2CB 15
in 67% yield. Deprotection of 15 with Bu4NF gave isomer V
quantitatively.
Scheme 7. Synthesis of N2CB-(Ca,Cb,N,N) (isomer II).
Synthesis of N2CB-(N,Ca,Ca,N) (isomer VI): So far, it has
been difficult to prepare the parent isomer VI by the strat-
egy shown above because acid condensation toward N-con-
fused pyrrole is essential at some stage. Nevertheless, the
acyl derivative could be prepared by the acid condensation
of monoacyl doubly N-confused tripyrrane 4. Thus, the reac-
tion of 4 with pyrrolyl carbinol 16 gave the monoacyl isomer
VI (17) in 24% yield (Scheme 11).
Synthesis of N2CB-(Ca,N,Ca,N) (isomer III): Isomer III can
be constructed from two singly N-confused dipyrromethane
units (Scheme 8). Thus, the reaction of N-protected N-con-
fused dipyrromethane 8 with N-confused dipyrromethane
monocarbinol 9 gave N-protected N2CB 10. In this reaction,
an excess amount of 8 was used to prevent self-condensation
of 9. The reaction yield reached up to 78% when 7 equiva-
lents of 8 were used. Importantly, 92% of 8 (corresponding
to 5.5 equiv) was recovered after the reaction, indicating a
smaller loss of the N-confused dipyrromethane unit. Depro-
tection of 10 with Bu4NF proceeded smoothly to give isomer
III in 97% yield.
Synthesis of N2CB-(N,Ca,Cb,N) (isomer VII): The synthesis
of isomer VII has already been reported.[11] Upon treatment
of doubly N-confused dipyrromethane dicarbinol 18 with
pyrrole in the presence of CF3CO2H, isomer VII was ob-
tained in 84% yield (Scheme 12).
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H. Furuta et al.
basic conditions, the product
yield was low. Additionally, iso-
merization from regular dipyr-
romethane to N-confused dipyr-
romethane was observed under
acidic conditions, such as in the
presence of AlCl3. Thus, less
bulky
tert-butyldimethylsilyl
(TBDMS) groups were used in
place of TIPS groups. Protec-
tion of regular dipyrromethane
with TBDMSCl proceeded
smoothly to give N,N’-bis-
TBDMS-dipyrromethane 19 in
79% yield. Bromination of 19
occurred preferentially at the b
position to give dibromo N,N’-
bis-TBDMS-dipyrromethane 20
in 49% yield. Treatment of 20
with
nBuLi
followed
by
C6F5CHO afforded
a
crude
product containing 21. Al-
though isolation of 21 in a pure
Scheme 9. Synthesis of N2CB-(Ca,N,Cb,N) (isomer IV).
form was difficult, acid conden-
sation of the crude product
with pyrrole successfully gave isomer VIII in 33% yield (2
steps); deprotection of the TBDMS groups occurred simul-
taneously.
Relative energy and conformation of N2CB: To investigate
the effect of confusion on the stability and structure of
bilane skeletons, a conformational search on unsubstituted
Scheme 10. Synthesis of N2CB-(Ca,N,N,Cb) (isomer V).
Scheme 12. Synthesis of N2CB-(N,Ca,Cb,N) (isomer VII).
Scheme 11. Synthesis of monoacyl isomer VI (17).
Synthesis of N2CB-(N,Cb,Ca,N) (isomer VIII): Isomer VIII
was synthesized from N,N’-diprotected regular dipyrrome-
thane (Scheme 13). In the early stage of synthetic study, we
tried to prepare N,N’-bis-TIPS-dipyrromethane as a key in-
termediate. Although the desired compound was obtained
by protection of regular dipyrromethane with TIPSCl under
Scheme 13. Synthesis of N2CB-(N,Cb,Ca,N) (isomer VIII).
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5,10,15-Triaryl Doubly N-Confused Bilanes
FULL PAPER
N2CBs was performed theoretically. Of course, numerous
conformations for N2CBs exist, so a thorough study was not
achieved. Nevertheless, significant results were obtained
through a synergy of systematic and arbitrary protocols.
Conformational studies were achieved as follows: When
3D structures were ignored, 10 representative conformers
could be described for regular bilane, which were catego-
rized into three groups: closed, bent, and linear
(Scheme 14). These three categories were also applied to
conformers of N2CBs. Starting from an arbitrary conforma-
À
tion, conformers were generated by rotating 6 C C bonds
that connect the pyrrole rings in steps of 608, namely, 6 dihe-
À
dral angles were considered for each C C bond and 46656
(=66) conformers were taken into consideration. The tenta-
tive stable conformers among the 46656 conformers were
calculated by the Monte Carlo method at the PM3 level of
semi-empirical calculations. Then, starting from the tentative
stable conformer, 729 (=36) conformers were systematically
À
generated by rotating the same 6 C C bonds again in steps
of 1208. All 729 conformers were optimized at the PM3
semi-empirical calculations and the stable closed, bent, and
linear conformers were selected. Finally, the stable closed,
bent, and linear conformers were further optimized at the
B3LYP/6-31G** DFT level of calculations. Molecular sym-
metry and overlapping of the conformers were not consid-
ered during these studies.
Scheme 14. Representative conformers of regular bilane.
The relative energies for stable conformers of N2CBs and
regular bilane thus obtained are summarized in Figure 2. In
the case of regular bilane, a closed conformer is most stable,
which is consistent with the favorable formation of tetrapyr-
rolic porphyrins in pyrrole/al-
while, N2CBs are less stable than regular bilane by only 3.7–
5.7 kcalmolÀ1. The loss of stability by confusion in the
bilane skeleton is not so significant, which is in marked con-
dehyde condensation reac-
tions.[16] Bent and linear con-
formers are less stable by 1.0–
1.2 kcalmolÀ1. The predomi-
nance of closed conformers re-
mains in isomers I–V of N2CB.
Interestingly, closed conform-
ers become less stable in iso-
mers VI–VIII, for which linear
or bent conformers are most
stable. Thus, the position of the
N-confused pyrrole affects the
conformation of the bilanes. A
characteristic feature of iso-
mers VI–VIII is the presence
of adjacent N-confused pyrrole
rings in the bilane skeleton. As
a
result,
isomers VI–VIII
might be not favorable for in-
tramolecular cyclization reac-
tions to give tetrapyrrolic N-
confused porphyrinoids, al-
though the relationship be-
tween bilane conformations
and intramolecular cyclization
reactions is not clear. Mean-
Figure 2. Relative energies for conformers of N2CBs and regular bilane. Optimized structures for regular
bilane are also shown.
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H. Furuta et al.
Table 1. Pyrrole rings that are the major contributors to the HOMO of
regular bilane and N2CBs.[a]
trast to the large destabilization of doubly N-confused por-
phyrins (ca. 38 kcalmolÀ1).[17]
Conformer Regular
bilane
N2CB
V
I
II
III IV
VI
VII
VIII
Reactivity of N2CB: To understand the reactivity of N2CBs,
predicting the most reactive pyrrole ring of the four pyrrole
rings would be helpful. In other words, we want to know
which pyrrole is more reactive: regular or N-confused. Be-
cause the preparation of porphyrinoids from oligopyrroles
usually relies on oxidation or electrophilic acid-catalyzed
condensation reactions, orbital coefficients in the HOMO
can be regarded as an approximate measure of reactivity.
Clearly, the HOMO of oligopyrrole is composed of pyrrole
p orbitals. The HOMOs of regular bilane and N2CBs for the
closed conformers are shown in Figure 3. The pyrrole rings
linear
bent
closed
BC
ABC
BC
C
C
C
B
BC
A
D
D
B
B
B
B
BC
BC
A
A
AB
AB
A
A
A
BC AD AD
[a] Normal text refers to the regular pyrrole ring, whereas italic text
refers to the N-confused pyrrole ring.
Some of the N2CBs could be used to prepare reported N-
confused porphyrinoids in an alternative synthetic pathway.
A synthetic study of new N-confused porphyrinoids by uti-
lizing other N2CBs is the next stage of our research.
Isomer III can be used as a precursor of N-confused N-
fused phlorin (Scheme 15).[9e] Thus, acylation of isomer III
afforded monoacylated product 22 and diacylated product
23 in 38 and 32% yield, respectively. Reduction of 22 gave
monocarbinol 24 and subsequent intramolecular acid con-
densation followed by DDQ oxidation afforded N-confused
N-fused phlorin 25 in 13% yield. The reaction yield is com-
parative to that reported for the [2+2] acid condensation
pathway. The lower yield was partly explained by scrambling
reactions because triply N-confused hexaphyrin was detect-
ed in the crude mixture.[9a]
Isomer V can be converted into corrorin.[18] Corrorin (26)
was previously obtained in 13% yield through a [2+2] acid-
catalyzed condensation reaction of N-confused dipyrrome-
thane. This time, the intramolecular oxidative cyclization re-
action of isomer V was examined. Treatment of isomer V
with DDQ (3.5 equiv) in CH3CN gave 26 in 92% yield
(Scheme 16). High efficiency of intramolecular cyclization
reaction might be rationalized by the conformation of iso-
mer V, which prefers the closed conformation, as shown in
Scheme 14.
Figure 3. HOMOs of regular bilane and N2CBs.
that are the major contributors
to the HOMO of regular bilane
and N2CBs for all three confor-
mations are listed in Table 1.
Essentially, the HOMO of
N2CB is composed of regular
pyrrole rings in almost all cases.
In addition, it is less dependent
on the conformation. The only
exceptions are isomers II and
VII, for which significant con-
tribution from the N-confused
pyrrole rings is recognized in
the HOMO. Specifically, the
b,b-linked doubly N-confused
dipyrromethane unit is highly
reactive. The other N-confused
pyrrole rings might be less reac-
tive than the regular pyrrole
rings.
Scheme 15. Synthesis of N-confused N-fused phlorin from N2CB-(Ca,N,Ca,N) (isomer III). DDQ=2,3-di-
chloro-5,6-dicyano-1,4-benzoquinone.
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5,10,15-Triaryl Doubly N-Confused Bilanes
FULL PAPER
Scheme 16. Synthesis of corrorin (26) from N2CB-(Ca,N,N,Cb) (iso-
mer V).
Figure 4. X-ray structure of the doubly N-confused biladiene copper(II)
complex (28). The pentafluorophenyl groups are omitted for clarity.
Thermal ellipsoids are shown at the 30% probability level.
When isomer VII was oxidized by DDQ, no cyclized
product was obtained. This is consistent with the fact that
the closed conformer would be less stable in isomer VII
(Figure 2). In turn, the formation of doubly N-confused bila-
diene 27, which was readily decomposed on silica gel and
opment of N-confused and N-fused porphyrinoid chemistry.
The formation of fascinating macrocyclic compounds by
using N2CBs can also be expected in the near future.
1
alumina, was suggested by H NMR spectroscopic analysis.
Although isolation of 27 itself was difficult, the addition of
CuACHTUNGTRENNUNG(OAc)2 to a solution of 27 in toluene caused a color
change from brown to red, which implied the formation of a
copper complex. After passing the crude mixture through a
pad of alumina and recrystallization from CH2Cl2/heptane,
the doubly N-confused biladiene copper(II) complex 28 was
obtained in 56% yield (Scheme 17). The X-ray structure of
28 is shown in Figure 4. Two copper atoms are chelated by
the doubly N-confused biladienes in a 2:2 fashion, forming a
unique helical structure. Similar structures were previously
reported for b-alkyl-substituted bilane derivatives.[19]
Experimental Section
General: All reactions were performed in oven-dried reaction vessels
under Ar or N2. Commercially available solvents and reagents were used
without further purification, unless otherwise stated. Dry THF (stabilizer
free) was purchased from Kanto. N-Bromosuccinimide (NBS) was recrys-
tallized from water. CH2Cl2 was distilled over CaH2. TLC was carried out
on aluminum sheets coated with silica gel 60 F254 (Merck). Preparative
separation was performed by silica gel flash column chromatography
(Kanto silica gel 60 N, spherical, neutral, 40–50 mm) and silica gel gravity
column chromatography (Kanto silica gel 60 N, spherical, neutral, 63–
210 mm). 1H NMR spectra were recorded in CDCl3 on a JEOL JNM-AL
series FTNMR (300 MHz) spectrometer at ambient temperature and
chemical shifts were reported relative to the residual solvent (d=
7.26 ppm). 13C NMR spectra were recorded in CDCl3 on the same instru-
ment and chemical shifts were reported relative to CDCl3 (d=
77.00 ppm). UV/Vis absorption spectra were recorded on a Shimadzu
UV-3150PC spectrometer. Mass spectra were recorded on a Bruker Dal-
tonics autoflex MALDI-TOF MS spectrometer. High-resolution mass
spectra were recorded on a JEOL JMS-T100CS spectrometer. Com-
pounds 1, 2, 7, and 8 were prepared as reported.[12] Synthesized tripyrrane
and bilane derivatives should be a mixture of diastereomers. In addition,
complicated long-range couplings existed due to 19F atoms and then com-
plete assignment of the NMR spectroscopy signals was nearly impossible,
especially for 13C NMR spectra. Thus, it was difficult to avoid ambiguity
to some degree. Many 13C NMR spectroscopy signals were observed as
doublets or multiplets; hence, superscript f, d, and m are used to show
the following signal patterns: f=further multiplet coupling due to remote
13C–19F coupling and signals were often not clear due to low intensity;
Scheme 17. Oxidation and copper(II) metallation of N2CB-(N,Ca,Cb,N)
(isomer VII).
thus, the chemical shift and 1J
ACTHNUTRGNEU(GN C,F) value would have some margin of
error up to 0.2 ppm (or 15 Hz); d=double singlets, probably from the
mixture of diastereomers; signal intensities were not always identical be-
cause they depended on the diastereomeric ratio; and m=multiple sin-
glets, probably from the mixture of diastereomers.
Conclusion
Compound 3: Trifluoroacetic acid (TFA; 30 mL, 0.40 mmol) was added to
a stirred solution of mixture containing
1 (1.0 g, 1.98 mmol) and 2
A series of doubly N-confused bilanes were synthesized and
their reactivity was analyzed theoretically as well as experi-
mentally. Although we succeeded in the preparation of
N2CBs, the reaction yields were limited in some cases, and
thus, the development of a new synthetic method for b-se-
lective reactions of the pyrrole ring can be expected. Never-
theless, the strategy and concept developed herein is appli-
cable to higher oligopyrroles and could accelerate the devel-
(0.828 g, 1.98 mmol) in CH2Cl2 under argon. The solution was stirred for
90 min and then neutralized with triethylamine. Removal of the solvent,
followed by column chromatography on silica gel (CH2Cl2/hexane 6:4
AHCTUNGTRNEG(UN v/v)), afforded 3 as a pale yellow, foamlike solid (79%, 1.42 g,
1.56 mmol). 1H NMR (CDCl3, 300 MHz): d=1.07 (d, J=7.5 Hz, 9H),
1.08 (d, J=7.5 Hz, 9H), 1.42 (septet, J=7.5 Hz, 3H), 5.74 (s, 1H), 5.77
(s, 1H), 5.92 (s, 1H), 6.04–6.06 (m, 1H), 6.21 (s, 1H), 6.62 (s, 3H), 6.75–
6.77 (m, 1H), 8.18 (brs, 1H), 9.45 ppm (brs, 1H); 13C NMR (CDCl3,
75 MHz): d=11.6, 17.7, 32.3, 32.7, 106.2,d 110.2, 110.9, 114.0,f 115.5,d
Chem. Eur. J. 2012, 18, 4380 – 4391
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4387

H. Furuta et al.
1
116.2,f 117.7,f 119.4, 122.4,d 122.6,d 125.2,d 130.6, 132.7,d 137.7 (d, J
G
lowed by column chromatography on silica gel (CH2Cl2/hexane 7:3 (v/v)),
249 Hz),f 140.1 (d, 1J(C,F)=247 Hz),f 142.1 (d, 1J(C,F)=257 Hz),f 144.2
G
ACHTUNGTRENNUNG
afforded isomer III as
a foamlike solid (97%, 0.81 g, 1.01 mmol).
(d, 1J(C,F)=250 Hz),f 143.1,d 144.9 (d, 1J(C,F)=246 Hz),f 171.7 ppm; IR
ACHTUNGTRENNUNG ACHTUNGTRENNUGN
1H NMR (CDCl3, 300 MHz): d=5.73 (s, 1H), 5.76 (s, 1H), 5.77 (s, 1H),
5.87–5.89 (m, 2H), 5.93–5.98 (m, 2H), 6.07 (s, 1H), 6.14–6.17 (m, 1H),
6.54 (s, 1H), 6.58 (s, 1H), 6.69–6.71 (m, 1H), 6.75–6.76 (m, 1H), 8.05
(brs, 1H), 8.18 ppm (brs, 3H); 13C NMR (CDCl3, 75 MHz): d=32.3,
33.1, 106.8,m 107.2, 108.0, 108.4, 115.4,f 116.3, 117.1,d 117.7,f 118.8, 121.0,d
(powder): n˜ =1628 cmÀ1 (CO); elemental analysis calcd (%) for
C42H32F15N3OSi: C 55.57, H 3.55, N 4.63; found: C 55.32, H 3.57, N 4.46.
Compound 4 (including a general procedures for deprotection): Com-
pound 3 (1.0 g, 1.1 mmol) was dissolved in dry THF at room temperature
in a 100 mL round-bottomed flask and purged with argon. Then Bu4NF
(1.14 mL, 1.14 mmol, 1.0m in THF) was added slowly for 5 min and the
resulting mixture was stirred for 1 h. After deprotection was complete (as
monitored by TLC), the reaction was quenched with water and the or-
ganic layer was separated, washed twice with water, and dried (Na2SO4).
Removal of the solvent, followed by column chromatography on silica
gel (CH2Cl2/hexane 7:3 (v/v)), afforded 4 as a foamlike solid (96%,
0.79 g, 1.05 mmol). 1H NMR (CDCl3, 300 MHz): d=5.75 (s, 1H), 5.78 (s,
1H), 5.96 (s, 1H), 6.07–6.09 (m, 1H), 6.16 (s, 1H), 6.60–6.64 (m, 1H),
6.68 (s, 1H), 6.78–6.80 (m, 1H), 8.27 (brs, 2H), 9.66 ppm (brs, 1H);
13C NMR (CDCl3, 75 MHz): d=32.2, 32.7, 106.3,d 108.2, 110.9, 113.9,f
115.7,d 116.1,f 116.5,d 117.5,f 118.8, 119.4, 120.7,d 122.6, 130.6, 132.3,d 137.7
122.0,d 126.5, 129.3, 130.3,d 131.3, 137.9 (d, J
N
(C,F)=240 Hz),f 140.0 (d, J-
ACHTUNGTRENNUNG
1
1
ACHTUNGTRENNUNG
calcd (%) for C37H27F15N4: C 55.37, H 2.14, N 6.98; found: C 55.59, H
2.26, N 6.68.
Compound 11: TFA (55.5 mL, 0.72 mmol) was added to a stirred solution
of 2 (2.1 g, 4.77 mmol) and 8 (3.16 g, 4.77 mmol) in CH2Cl2 under argon.
The solution was stirred for 90 min and then neutralized with triethyl-
AHCTUNGERTGaNNUN mine. Removal of the solvent, followed by column chromatography on
silica gel (CH2Cl2/hexane 5:95 (v/v)), afforded 11 as a fluorescent orange
solid (72%, 3.0 g, 3.45 mmol). 1H NMR (CDCl3, 300 MHz): d=1.05 (d,
J=7.5 Hz, 36H), 1.40 (septet, J=7.5 Hz, 6H), 5.75 (s, 2H), 5.85–5.92 (m,
2H), 6.10–6.12 (m, 2H), 6.54 (s, 2H), 6.68–6.71 (m, 2H), 8.18 and
8.31 ppm (both brs, 1H in total)* [*NH signals for each diastereomer
would be observed separately]; 13C NMR (CDCl3, 75 MHz): d=11.7,
(d, 1J
257 Hz),f 143.1,d 143.8 (d, 1J
N
E
ACHTUNGTRNE(NUNG C,F)=
U
ACHTUNGTRENNUNG
17.7, 32.5, 106.5, 110.1, 122.3, 123.3, 124.9, 130.0, 137.6 (d, 1J
ACHTUNGTRENNUNG
1
1
250 Hz),f 139.8 (d, J(C,F)=252 Hz),f 144.9 ppm (d, J
ACTHNUGTRENNUGN ACHTUNGTRENNNUG
emental analysis calcd (%) for C44H53F10N3Si: C 60.74, H 6.14, N 4.83;
found: C 60.52, H 6.15, N 4.76.
Isomer I (including a general procedures for reduction): Compound 4
(0.75 g, 1.0 mmol) in THF (30 mL) and methanol (6 mL) in a 50 mL
round-bottomed flask was treated with the portions of NaBH4 (0.94 g,
25.0 mmol). After reduction was complete (as monitored by TLC), the
reaction mixture was poured into a saturated aqueous solution of NH4Cl
(20 mL) and CH2Cl2 (40 mL) in a 200 mL beaker. The organic layer was
separated, washed twice with water, and dried (Na2SO4). Removal of the
solvent under vacuum yielded monocarbinol 5 as a foamlike solid. Then
pyrrole (1.73 mL, 25.0 mmol) was added and the reaction mixture was
stirred for 5 min under argon. TFA (19 mL, 0.25 mmol) was then added
and the reaction mixture was stirred for an additional 1 h and quenched
with triethylamine. Removal of excess pyrrole, followed by column chro-
matography on silica gel (CH2Cl2/hexane 6:4 (v/v)), afforded isomer I as
an off-white foamlike solid (72%, 0.58 g, 0.72 mmol). 1H NMR (CDCl3,
300 MHz): d=5.70 (s, 1H), 5.72 (s, 1H), 5.82–5.86 (m, 3H), 5.92–5.95
(m, 2H), 6.12–6.15 (m, 2H), 6.45 (s, 1H), 6.62 (s, 1H), 6.71 (d, J=1.2 Hz,
1H), 6.78 (d, J=2.7 Hz, 1H), 8.10–8.20 ppm (m, 4H); 13C NMR (CDCl3,
75 MHz): d=32.6, 32.8, 33.5, 106.6,m 107.1,m 107.7,d 108.4,d 108.7, 109.0,d
115.7,d 116.2,f 116.9,d 118.0,f 118.2,m 119.2, 121.3,m 121.7,m 127.4,m 128.6,m
Compound 12: Compound 11 (2.22 g, 2.56 mmol) was dissolved in dry
THF at room temperature and treated with Bu4NF, according to the gen-
eral procedure. Removal of the solvent, followed by column chromatog-
raphy on silica gel (CH2Cl2/hexane 4:6 (v/v)), afforded 12 as a foamlike
solid (88%, 1.25 g, 2.24 mmol). 1H NMR (CDCl3, 300 MHz): d=5.75 (s,
2H), 5.87–5.90 (m, 2H), 6.08 (s, 2H), 6.59 (s, 2H), 6.75 (d, J=1.8 Hz,
2H), 8.15 (brs, 2H), 8.23 ppm (brs, 1H); 13C NMR (CDCl3, 75 MHz):
d=32.4, 106.7, 108.1, 116.2, 118.5, 121.6, 129.8, 137.6 (d, 1J
ACHTUNGTRENNUNG
1
1
253 Hz),f 139.9 (d, J(C,F)=253 Hz),f 144.8 ppm (d, J
ACTHNUGTRENNUGN ACHTUNGTRENNNUG
Compound 13: A solution of EtMgBr (7.18 mL, 7.18 mmol, 1.0m in
THF) was carefully added to a stirred solution of 12 (1.0 g, 1.79 mmol) in
THF (10 mL) under argon. The mixture was stirred at room temperature
for 20 min and then cooled to À788C. A solution of S-2-pyridyl penta-
fluorobenzothioate (602 mg, 1.97 mmol) in THF (5 mL) was then added
over 1 min. The solution was maintained at À788C for 30 min and the
temperature was raised to 08C. The reaction was quenched with a satu-
rated aqueous solution of NH4Cl and the mixture was allowed to warm
to ambient temperature, poured into CH2Cl2, washed with water, and
then dried (Na2SO4). After filtration, the solvent was removed under re-
duced pressure to afford a dark foam, which was purified by column
chromatography on silica gel (CH2Cl2/hexane 7:3 (v/v)) to give 13 as a
golden amorphous solid (55%, 0.74 g, 0.99 mmol). 1H NMR (CDCl3,
300 MHz): d=5.69 (s, 1H), 5.76 (s, 1H), 5.86–5.98 (m, 2H), 6.07 (s, 1H),
6.51 (s, 1H), 6.59 (s, 1H), 6.75–6.77 (m, 1H), 6.99–7.03 (m, 1H), 8.12
(brs, 1H), 8.22 (brs, 1H), 9.87 ppm (brs, 1H); 13C NMR (CDCl3,
75 MHz): d=32.1, 32.3, 106.6, 107.9, 108.2, 113.5,f 116.3, 116.4,f 117.8,f
131.6,m 132.3,m 138.1 (d, 1J
(C,F)=251 Hz),f 140.6 (d, 1J(C,F)=244 Hz),f
ACHUTGTNRENNUG CAHTUNGTRENNUGN
145.3 ppm (d, 1J(C,F)=245 Hz)f; elemental analysis calcd (%) for
ACHTUNGTRENNUNG
C37H27F15N4: C 55.37, H 2.14, N 6.98; found: C 55.70, H 2.17, N 6.93.
Compound 10: A sample of 2-pentafluorobenzoyl-5-pentafluorophenyl-1-
aza-10-carbadipyrromethane (1.35 g, 2.67 mmol) was reduced with
NaBH4 (2.52 g, 66.8 mmol), according to the general procedure, giving 9
in a quantitative manner as a pale yellow, foamlike solid. Compound 9
was treated with 8 (8.75 g, 18.7 mmol) in CH2Cl2 and stirred for 5 min
under argon before TFA (62 mL, 0.8 mmol) was added slowly to the reac-
tion mixture. After stirring for 1 h at room temperature, triethylamine
(0.11 mL, 0.8 mmol) was added and removal of the solvent, followed by
column chromatography on silica gel (CH2Cl2/hexane 6:4 (v/v)), afforded
10 as a pale yellow foamlike solid (78%, 2.0 g, 2.09 mmol), along with re-
covered 8 (6.87 g, 14.7 mmol). 1H NMR (CDCl3, 300 MHz): d=1.05 (d,
J=7.5 Hz, 18H), 1.39 (septet, J=7.5 Hz, 3H), 5.71 (s, 1H), 5.75 (s, 2H),
5.81 (d, J=2.7 Hz, 1H), 5.86 (s, 1H), 5.95–6.01 (m, 2H), 6.12–6.14 (m,
2H), 6.50 (s, 1H), 6.55 (s, 1H), 6.69 (s, 1H), 6.73 (s, 1H), 7.96–8.20 ppm
(m, 3H); 13C NMR (CDCl3, 75 MHz): d=11.5, 17.6, 32.3, 32.1, 106.6,m
106.7,m 107.1, 108.4,m 109.9,d 115.4,f 116.2, 117.0,d 117.8,f 122.0,m 122.4,d
118.9, 120.1, 121.0, 126.3, 127.0,m 127.7, 131.1, 131.6, 137.6 (d, 1J
251 Hz),f 140.0 (d, 1J(C,F)=253 Hz),f 142.4 (d, 1J(C,F)=258 Hz),f 143.9
(d, 1J(C,F)=252 Hz),f 144.8 (d, 1J(C,F)=253 Hz),f 172.9 ppm; IR
(powder): n˜ = 1625 cmÀ1 (CO).
ACHTUNGTRENNUNG(C,F)=
E
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
Isomer IV: Compound 13 (0.70 g, 0.93 mmol) was reduced with NaBH4
(0.88 g, 23.3 mmol), according to the general procedure. The resulting
carbinol 14 was treated with pyrrole (1.6 mL, 13.3 mmol) in the presence
of TFA (14.4 mL, 0.19 mmol) for 1 h and then neutralized with triethyl-
AHCTUNGERTGaNNUN mine. Removal of the solvent, followed by column chromatography on
silica gel (CH2Cl2/hexane 6:4 (v/v)), afforded isomer IV as a pale yellow
foamlike solid (76%, 0.57 g, 0.71 mmol). 1H NMR (CDCl3, 300 MHz):
d=5.68 (s, 1H), 5.75 (s, 1H), 5.82 (s, 1H), 5.85–5.89 (m, 3H), 6.03–6.05
(m, 2H), 6.16–6.17 (m, 1H), 6.48 (s, 1H), 6.56 (s, 1H), 6.75 (s, 2H), 8.04
(brs, 1H), 8.15–8.25 ppm (m, 3H); 13C NMR (CDCl3, 75 MHz): d=32.3,
33.0, 106.8,m 107.2, 108.0,d 108.7, 115.3,f 116.3,d 117.7,f 118.4, 118.6,m
122.7, 125.3,d 126.4,m 129.2,m 130.2,d 131.8,m 137.8 (d, 1J
(C,F)=241 Hz),f
ACHTUNGTRENNUNG
140.0 (d, 1J(C,F)=247 Hz),f 144.9 ppm (d, 1J(C,F)=242 Hz)f; elemental
G
ACHTUNGTRENNUNG
analysis calcd (%) for C46H37F15N4Si: C 57.62, H 3.89, N 5.84; found: C
57.83, H 3.98, N 5.81.
Isomer III: Compound 10 (1.0 g, 1.04 mmol) was deprotected with
Bu4NF, according to the general procedure. Removal of the solvent, fol-
ACTHNGUTERNNUG
121.6,d 122.1,d 127.6, 129.3,m 129.9,d 137.6 (d, 1J(C,F)=250 Hz),f 140.2 (d,
4388
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 4380 – 4391

5,10,15-Triaryl Doubly N-Confused Bilanes
FULL PAPER
1J
(C,F)=250 Hz),f 144.8 ppm (d, 1J
E
18.9, 26.1, 36.4, 97.4, 116.1, 116.2,f 125.6, 136.9, 137.8 (d, 1J
ACHTUNGTRENNUNG
1
1
calcd for C37H17F15N4 [M+]: 802.12137; found: 802.12586.
256 Hz),f 140.4 (d, J(C,F)=253 Hz),f 145.2 ppm (d, J
ACTHNGUTRENNUG CAHTUNGTRENNUNG
emental analysis calcd (%) for C27H35Br2F5N2Si2: C 46.42, H 5.05, N 4.01;
found: C 47.13, H 5.08, N 4.01 (this compound undergoes gradual decom-
position even in the solid state).
Compound 15: A solution of 7 (400 mg, 1.28 mmol) in CH2Cl2 (5 mL)
was added dropwise to a stirred solution of 2 (2.0 g, 4.77 mmol, 3.7 equiv)
and CF3CO2H (40 mL, 0.520 mmol, 0.4 equiv) in CH2Cl2 (10 mL) at 08C.
The resulting mixture was warmed to ambient temperature and stirred
for 12 h. Then, the reaction was quenched with an aqueous solution of
NaOH and diluted with CH2Cl2 and water. The organic phase was sepa-
rated, washed with water, dried over sodium sulfate, and evaporated in
vacuo. The residue was separated by column chromatography on silica
gel using hexane/CH2Cl2 4:1 (v/v) as the eluent. The first fraction (Rf =
0.80, hexane/CH2Cl2 1:1 (v/v)) afforded 15 as a clear oil (67%, 950 mg,
0.85 mmol). 1H NMR (CDCl3, 300 MHz): d=1.09 (d, J=7.5 Hz, 18H),
1.10 (d, J=7.5 Hz, 18H), 1.44 (septet, J=7.5 Hz, 6H), 5.79 (s, 3H), 5.85
(d, J=3.0 Hz, 2H), 5.90 (d, J=3.0 Hz, 2H), 6.15–6.20 (m, 2H), 6.59–6.63
(m, 2H), 6.75–6.79 (m, 2H), 8.08 ppm (brs, 2H); 13C NMR (CDCl3,
75 MHz): d=11.6, 17.7, 32.4, 33.3, 106.5,d 107.6,d 110.1, 122.4,d 122.8,m
Isomer VIII: nBuLi (5.38 mL, 3.44 mmol, 4.0 equiv) was added dropwise
to a stirred solution of 20 (600 mg, 0.86 mmol) in anhydrous THF at
À788C and the resulting mixture was stirred for 1 h at À788C. Penta-
fluorobenzaldehyde (265 mL, 2.15 mmol, 2.5 equiv) in THF (15 mL) was
added slowly and stirring was continued for an additional 1 h at À788C.
The cooling bath was removed and the mixture was allowed to warm to
room temperature. Then a saturated aqueous solution of NH4Cl was
added and the mixture was diluted with Et2O. The organic layer was sep-
arated, dried (Na2SO4), and concentrated under reduced pressure. The
resulting pale yellow oil, including 21, was used for the next step without
further purification. Pyrrole (3.7 mL, 53.4 mmol) was added to the above
oil and stirred under argon for 5 min. Then TFA (10 mL, 0.13 mmol) was
added and the solution was stirred for an additional 2 h. The reaction
was quenched with triethylamine and excess pyrrole was removed under
vacuo. The residue was purified by column chromatography on silica gel
(CH2Cl2/hexane 6:4 (v/v)) to afford isomer VIII as a pale yellow foamlike
solid (33%, 0.228 g, 0.284 mmol). 1H NMR (CDCl3, 300 MHz): d=5.73
(s, 2H), 5.78 (s, 1H), 5.92 (s, 2H), 5.98 (s, 2H), 6.13–6.16 (m, 2H), 6.55
(s, 2H), 6.67–6.71 (m, 2H), 8.06 (brs, 2H), 8.18 ppm (brs, 2H); 13C NMR
(CDCl3, 75 MHz): d=32.3, 33.1, 106.8,d 107.8, 108.4, 114.9,f 116.7, 117.2,
125.2,d 127.0,m 131.2, 137.6 (d, 1J(C,F)=249.1 Hz),f 140.0 (d, 1J
ACTHNUTRGENNUG AHCUTNGTREN(NUGN C,F)=
ACTHNUTRGNEUNG
252.8 Hz),f 144.9 ppm (d, 1J(C,F)=241.7 Hz)f; HRMS (ESI+): m/z calcd
for C55H57F15N4Si2 [M+H]+: 1115.39605; found: 1115.39680.
Isomer V: Compound 15 (67 mg, 0.061 mmol) was deprotected with
Bu4NF, according to the general procedure. Removal of the solvent, fol-
lowed by column chromatography on silica gel (CH2Cl2/hexane=6/4
ACHTUNGTRENNUNG(v/v)), afforded isomer V as a foamlike solid (99%, 49 mg, 0.061 mmol).
1H NMR (CDCl3, 300 MHz): d=5.75 (s, 2H), 5.78 (s, 1H), 5.86–5.91 (m,
4H), 6.08 (s, 2H), 6.59 (s, 2H), 6.75–6.77 (m, 2H), 8.11 (brs, 2H),
8.16 ppm (brs, 2H); 13C NMR (CDCl3, 75 MHz): d=32.3, 33.2, 106.8,m
107.7,d 108.0,m 115.8,f 116.3, 117.7,f 118.7,d 121.0,d 127.1,d 130.9,d 137.6 (d,
ACTHNUTRGNEUNG
117.5,f 122.2,d 128.6,d 130.1,d 137.7 (d, 1J(C,F)=251 Hz),f 140.0 (d, 1J-
ACHUTNGRENNUG CAHTUNGTRENNUGN
(C,F)=253 Hz),f 144.8 ppm (d, 1J(C,F)=242 Hz)f; HRMS (ESI+): m/z
calcd for C37H17F15N4 [M]+: 802.12137; found: 802.12383.
1J(C,F)=253 Hz),f 140.0 (d, 1J(C,F)=253 Hz),f 144.8 ppm (d, 1J
ACHTUNGTRENNUNG ACHTUNRTGENNUNG ACHTNUGERTN(NUGN C,F)=
Compound 22: A solution of EtMgBr (5.0 mL, 5.0 mmol, 1.0m in THF)
was added dropwise to a stirred solution of isomer III (1.0 g, 1.25 mmol)
in THF (10 mL) under argon. After stirring at room temperature for
247 Hz)f; HRMS (ESI+): m/z calcd for C37H18F15N4 [M+H]+: 803.12919;
found: 803.13118.
20 min,
a solution of S-2-pyridyl pentafluorobenzothioate (382 mg,
Compound 17: TFA (7.8 mL, 0.1 mmol) was added to a stirred mixture of
4 (0.38 g, 0.51 mmol) and 16 (0.16 g, 0.61 mmol) in CH2Cl2 (20 mL) at
room temperature. The reaction mixture was quenched with triethyla-
mine after 1 h and evaporated in vacuo. Removal of the solvent, followed
by column chromatography on silica gel (CH2Cl2/hexane 9:1 (v/v)), af-
forded 17 as a pale yellow foamlike solid (24%, 0.12 g, 0.12 mmol).
1H NMR (CDCl3, 300 MHz): d=5.65 (s, 1H), 5.69 (s, 1H), 5.74 (s, 1H),
5.83 (s, 1H), 5.99–6.01 (m, 2H), 6.10 (s, 1H), 6.50 (s, 1H), 6.62 (s, 2H),
6.74–6.77 (m, 2H), 8.20 (brs, 2H), 8.49 (brs, 1H), 9.40 ppm (brs, 1H);
HRMS (ESI+): m/z calcd for C44H17F20N4O [M+H]+: 997.10830; found:
997.10804.
1.25 mmol) in THF (5 mL) was added over 1 min at À788C. The temper-
ature was raised to 08C after stirring the resulting mixture at À788C for
30 min. The reaction was quenched with a saturated aqueous solution of
NH4Cl and the mixture was allowed to warm to ambient temperature,
poured into CH2Cl2, washed with water, and then dried (Na2SO4). After
filtration, the solvent was removed under reduced pressure to give a dark
foam, which was purified by column chromatography on silica gel
(CH2Cl2/EtOAc=98/2 (v/v)), to give 22 as a pale yellow solid (38%,
0.45 g, 0.45 mmol). 1H NMR (CDCl3, 300 MHz): d=5.69 (s, 1H), 5.72 (s,
1H), 5.77 (s, 1H), 5.89–5.99 (m, 4H), 6.14–6.18 (m, 1H), 6.49 (s, 1H),
6.53 (s, 1H), 6.70–6.71 (m, 1H), 6.97–6.99 (m, 1H), 8.04 (brs, 2H), 8.18
(brs, 1H), 9.80 ppm (brs, 1H); 13C NMR (CDCl3, 75 MHz): d=32.1,
32.3, 33.1, 106.9,d 107.5,m 108.0,m 108.4, 113.4,f 115.1,f 116.0,f 116.6, 117.2,d
117.5,f 119.6, 122.4,m 125.5,d 126.5,d 128.1,m 128.8,m 129.4, 130.1,d 131.7,
Compound 19: A stirred suspension of NaH (769 mg, 19.2 mmol) in THF
(150 mL) was treated with 5-pentafluorophenyldipyrromethane (2.0 g,
6.4 mmol) at 08C. When the evolution of gas ceased, the mixture was
stirred for 1 h at room temperature before being treated with tert-butyldi-
methylsilylchloride (1.93 g, 12.8 mmol). After 12 h, the reaction mixture
was quenched using saturated aqueous NH4Cl and diluted with CH2Cl2.
The organic layer was separated, washed with water and brine, and dried
(Na2SO4). Removal of solvent, followed by column chromatography on
silica gel (CH2Cl2/hexane 1:9 (v/v)), afforded 19 as a white crystalline
solid (79%, 2.73 g, 5.0 mmol). 1H NMR (CDCl3, 300 MHz): d=0.19 (s,
6H), 0.35 (s, 6H), 0.81 (s, 18H), 5.58 (s, 1H), 5.62 (brs, 2H), 6.13 (t, J=
3.0 Hz, 2H), 6.77–6.79 ppm (m, 2H); 13C NMR (CDCl3, 75 MHz): d=
À4.6, À2.8, 19.0, 26.2, 36.6, 109.5, 113.5, 117.8,f 126.1, 136.8, 137.6 (d, 1J-
137.7 (d, 1J(C,F)=250 Hz),f 140.1 (d, 1J(C,F)=240 Hz),f 142.5 (d, 1J-
ACTHNUTRGENNUG CAHTUNGTRENNUGN
(C,F)=258 Hz),f 143.9 (d, 1J(C,F)=255 Hz),f 144.8 ppm (d, 1J
AHCTUNGTRENGNUN ACHTUNRTGENNUNG ACHTUNGTRENNUNG(C,F)=
244 Hz)f; IR (powder): n˜ =1634 cmÀ1 (CO); elemental analysis calcd (%)
for C44H16F20N40: C 53.03, H 1.62, N 5.62; found: C 53.11, H 1.66, N 5.95.
Compound 28: A solution of isomer VII (50 mg, 62 mmol, 1 equiv) in
CH3CN (50 mL) was added dropwise over 5 min to DDQ (50 mg,
220 mmol, 3.5 equiv) in CH3CN (50 mL) at ambient temperature. After
stirring for 10 min, the reaction mixture was concentrated under reduced
pressure and the residue was dissolved in CH2Cl2 (20 mL). NaOAc·3H2O
(85 mg, 620 mmol, 10 equiv) and CuII
ACTHNUTRGEN(UNG OAc)2·H2O (62 mg, 310 mmol,
ACHTUNGTRENNUNG ACHTUNRTGENNUNG ACHTNUGERTN(NUGN C,F)=
(C,F)=255 Hz),f 140.1 (d, 1J(C,F)=253 Hz),f 144.8 ppm (d, 1J
247 Hz)f; elemental analysis calcd (%) for C27H37F5N2Si2: C 59.97, H
6.90, N 5.18; found: C 59.88, H 6.93, N 5.15.
5 equiv) were added and the mixture was stirred at ambient temperature
for 2 h. The resulting mixture was passed through a pad of alumina and
the filtrate was evaporated to give 28, which was further purified by re-
crystallization from CH2Cl2/hexane (30 mg, 17 mmol, 56% yield). The
copper(II) complex 28 was NMR silent.
Compound 20: A solution of 19 (1.5 g, 2.78 mmol) in dry THF (25.0 mL)
at À788C under argon was treated with NBS (1.04 g, 5.83 mmol). The re-
action mixture was stirred for 1 h at À788C and gradually warmed up to
À208C. After adding hexane (50 mL) and water (5 mL), the mixture was
warmed up to ambient temperature. The organic layer was separated,
dried (Na2SO4), and concentrated. The resulting pale yellow solid was pu-
rified by column chromatography on alumina with hexane as the eluent
to afford 20 as a white solid (49%, 0.95 g, 1.36 mmol). 1H NMR (CDCl3,
300 MHz): d=0.19 (s, 6H), 0.35 (s, 6H), 0.81 (s, 18H), 5.47 (s, 1H), 5.66
(s, 2H), 6.73 ppm (s, 2H); 13C NMR (CDCl3, 75 MHz): d=À4.4, À2.8,
Calculation details: Conformational search was performed with the Spar-
tan’10 program package. DFT calculations were performed with the
Gaussian 09 program package[20] without symmetry assumption. The geo-
metries were fully optimized at the Beckeꢁs three-parameter hybrid func-
tional[21] combined with the Lee–Yang–Parr correlation functional,[22] ab-
breviated as the B3LYP level of DFT. Stationary points were confirmed
by frequency analysis, in which no imaginary frequency was found.
Chem. Eur. J. 2012, 18, 4380 – 4391
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www.chemeurj.org
4389

H. Furuta et al.
X-ray crystallography: X-ray analysis of N,N’-protected doubly N-con-
fused dipyrromethane was performed on a SMART APEX diffractome-
ter equipped with a CCD detector (Bruker AXS) using MoKa (graphite,
monochromated, l=0.71069 ꢂ) radiation. X-ray analysis of 28 was per-
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formed on
a Saturn diffractometer equipped with a CCD detector
(Rigaku) using MoKa (graphite, monochromated, l=0.710747 ꢂ) radia-
tion. The structure was solved by the direct method of SHELXS-97 and
refined by using the SHELXL-97 program.[23] The positional parameters
and thermal parameters of non-hydrogen atoms were refined anisotropi-
cally on F2 by the full-matrix least-squares method except for disordered
positions of 28. Hydrogen atoms were placed at calculated positions and
refined riding on their corresponding carbon atoms.
CCDC-843906 (N,N’-protected doubly N-confused dipyrromethane) and
CCDC-843907 (28) contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from
The
Cambridge
Crystallographic
Data
Centre
via
www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgements
The present work was supported by a Grant-in-Aid for Scientific Re-
search (21750047, 21108518, and 22350020) and the Global COE Pro-
gram “Science for Future Molecular Systems” from the Ministry of Edu-
cation, Culture, Sports, Science and Technology of Japan.
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Chem. Eur. J. 2012, 18, 4380 – 4391

5,10,15-Triaryl Doubly N-Confused Bilanes
FULL PAPER
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
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Received: September 28, 2011
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Published online: February 23, 2012
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ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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