Heterohelicenes with embedded P-chiral 1H-phosphindole or dibenzophosphole units: Diastereoselective photochemical synthesis and structural characterization

Article abstract of DOI:10.1002/chem.201300844

The oxidative photocyclization reactions of olefins that contain 1H-phosphindole or dibenzophosphole substituents have been applied to the synthesis of P/N-bi-heterosubstituted dimeric helicenes, as well as of new [6]- and [8]phosphahelicenes. In these photocyclization processes, the configuration of the stereogenic phosphorus center dictates the sense of helical chirality. Thus, by starting from enantiomerically pure P-menthylphosphole-oxide units, this method affords enantiopure helical compounds. The helical phosphine oxides were characterized by X-ray diffraction. After reduction of the phosphine-oxides, the corresponding helical phosphines have been used as ligands in transition-metal complexes. The X-ray crystal structure of a gold chloride complex of a [6]helicene is reported. From phosphindoles to helicenes: Olefins with 1H-phosphindole or dibenzophosphole substituents are suitable precursors for P/N-bi-heterosubstituted dimeric helicenes, as well as for new [6]- and [8]phosphahelicenes. The highly diastereoselective oxidative photocyclization of these olefins opens up access to enantiomerically pure helical derivatives. The structural characterization of a helical phosphine oxide, sulfide, and gold complex is reported. Copyright

Full text of DOI:10.1002/chem.201300844

FULL PAPER
DOI: 10.1002/chem.201300844
Heterohelicenes with Embedded P-Chiral 1H-Phosphindole or
Dibenzophosphole Units: Diastereoselective Photochemical Synthesis and
Structural Characterization
Keihann Yavari, Pascal Retailleau, Arnaud Voituriez,* and Angela Marinetti*[a]
Abstract: The oxidative photocycliza-
tion reactions of olefins that contain
1H-phosphindole or dibenzophosphole
substituents have been applied to the
synthesis of P/N-bi-heterosubstituted
dimeric helicenes, as well as of new [6]-
and [8]phosphahelicenes. In these pho-
tocyclization processes, the configura-
tion of the stereogenic phosphorus
center dictates the sense of helical chi-
G
E
phosphine oxides were characterized
by X-ray diffraction. After reduction of
the phosphine-oxides, the correspond-
ing helical phosphines have been used
as ligands in transition-metal com-
plexes. The X-ray crystal structure of a
gold chloride complex of a [6]helicene
is reported.
Introduction
bis(diphenylphosphino)-1,1’-binaphthyl)
enantioselective
[2+2+2] cyclization[4] and palladium-promoted intramolecu-
lar P-arylation[5] reactions as the key steps, respectively.
Both methods afford helical derivatives in which phosphole
units are located in the internal section of the polyaromatic
sequence (Figure 1, left). Therefore, to increase the structur-
The ortho-fused polycyclic p frameworks of helicenes are
known to afford extremely appealing and useful physico-
chemical properties for various applications, such as lumi-
nescent materials, non-linear optics, wave guides, polymers,
photovoltaic energy storage, etc. Biological applications and
the use of helicenes as chiral auxiliaries have also been envi-
sioned.[1]
The embedding of phosphorus moieties into their polyaro-
matic sequence is expected to modulate, by itself, the physi-
cochemical properties of helicenes. Moreover, it opens up
an even more extended range of properties and applications
of these compounds, based on the potential coordination of
the phosphorus atoms to a variety of transition metals.[2,3]
Therefore, it is expected that unprecedented tools for both
materials science and innovative catalytic applications might
be developed in the future by taking advantage of such heli-
cenes. In this context and irrespective of the targeted appli-
cation field, versatile high-yielding synthetic access to phos-
phahelicenes and a variety of molecular engineering strat-
egies are key prerequisites for the successful development
of new practical applications. So far, synthetic strategies
have been reported by the groups of Tanaka and Nozaki,
which make use of RhI/H8-BINAP-catalyzed (BINAP=2,2’-
Figure 1. Representation of the known classes of phosphahelicenes, from
references [4], [5] (left), and [6] (right).
al diversity in these series, we recently designed a new
family of phosphahelicenes in which the phosphorus group
lay on the external edge of the polyaromatic sequence
(Figure 1, right).[6]
For their synthesis, we adapted the well-known photo-
chemical oxidative cyclization reaction of diarylethenes[7] to
phosphindole-substituted olefins, as shown in Scheme 1. We
have demonstrated that phosphindole-substituted 2-octenes
(I) undergo photochemical cyclization into [6]- and [7]heli-
cenes that are terminated by a phosphole moiety. These
photocyclization reactions are highly diastereoselective and
they afford helicenes with RP*,P* relative configurations as
the sole isolated products.
[a] K. Yavari, Dr. P. Retailleau, Dr. A. Voituriez, Dr. A. Marinetti
Institut de Chimie des Substances Naturelles
CNRS UPR 2301, Centre de Recherche de Gif
1, av. de la Terrasse, 91198 Gif-sur-Yvette (France)
Fax : (+33)1-69077247
Following these initial studies, we have expanded the
scope of our synthetic approach by varying both the phos-
phorus-containing unit and the polyaromatic unit on the ole-
finic substrate (I). Herein, we report that this method is suit-
E-mail: arnaud.voituriez@cnrs.fr
angela.marinetti@cnrs.fr
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201300844.
Chem. Eur. J. 2013, 19, 9939 – 9947
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
9939

Scheme 3). These two fragments were connected onto the
same olefin group through two sequential palladium-cata-
lyzed Suzuki reactions. 11-BromonaphthoACTHNUTRGNEUNG[1,2-f]quinoline (1)
was prepared through a photochemical cyclodehydrogena-
tion reaction of the corresponding 6-(4-bromostyryl)quino-
line.[12] Then, compound 1 was submitted to a coupling reac-
tion with bis-boronate 2[13] in the presence of [Pd
ACHTNUTRGNEGNU(PPh3)4] to
afford the olefinic boronate 3 in 46% yield. The second cou-
pling step, between compound 3 and phosphindole oxide tri-
flate (RP)-4,[6] was performed in a THF/water mixture, in the
presence of Cs2CO3, with 10 mol% [PdCl2ACHTNUTRGNEU(GN SPhos)2] as the
catalyst (Scheme 2). The desired stilbene, (RP)-5, was ob-
tained in 75% yield.
In these reactions, we used the RP epimer of the P-stereo-
genic 1-(1R,2S,5R)-menthyl-1H-phosphindole triflate (4; for
clarity, the stereochemical descriptors of the menthyl frag-
ment are omitted herein and the RP/SP labels indicate the
configuration of the phosphorus atoms). This epimer was
obtained in its pure form by flash chromatography on silica
gel of the corresponding epimeric mixture.[6] Its coupling
with 3 afforded the stilbene derivative (RP)-5 which dis-
played an [a]D value of +35 (c=0.4, CHCl3). Compound
(RP)-5 was subjected to photochemical cyclodehydrogena-
tion under standard conditions, that is, in toluene/THF (1:1,
6ꢁ10À4 mmolmLÀ1) with I2 as the oxidant in the presence of
propylene oxide (Scheme 3). This reaction proceeded as ex-
Scheme 1. Photochemical synthesis of phosphorus-containing helicenes.[6]
able for the synthesis of P/N-bi-heterosubstituted dimeric
helicenes, as well as for the syntheses of [6]- and [8]heli-
cenes in high yields starting from dibenzophospholes as
structural units. Moreover, we show that the two epimers of
the P-menthyl-substituted substrates may afford different
product distributions in these photochemical cyclization re-
actions. Finally, we demonstrate that both [6]- and [8]heli-
cenes with trivalent phosphorus groups are effective ligands
for transition-metal complexes.
Results and Discussion
Azahelicenes have been known since 1969[8] and recent stud-
ies have demonstrated their potential, as well as the poten-
tial of their N-oxides and salts, in asymmetric catalysis.[9] On
the other hand, myriad ligands and catalysts have been re-
ported that synergistically combine phosphorus and nitrogen
functionalities into the same entity.[10] However, helical com-
pounds of this class in which phosphorus functions are ap-
pended onto an azahelicene structure are extremely rare.[11]
In this respect, bi-heterohelicenes that combine phosphole
and pyridine groups are relevant target compounds for illus-
trating the scope of our synthetic approach to the oxidative
photocyclization of suitable diarylolefins shown in
Scheme 1. Herein, we show that bi-heterohelicenes can be
readily obtained by using this photocyclization strategy, by
combining 1H-phosphindol-5-yl and naphthoquinolin-11-yl
fragments as the key structural units (Scheme 2 and
Scheme 3. Photochemical synthesis of dimeric bi-heterohelicenes. i) I2,
propylene oxide, toluene/THF (1:1), hn 150 W, 1.5 h, 49%.
pected, thus leading to a [6]-azahelicene terminated by a
phosphole moiety. However, during the reaction, the azahe-
licene started to dimerize through an intermolecular photo-
chemical [2+2] cyclization of the phosphindole moieties,[14]
as has previously been noted for its analogous carbohelicene
derivatives.[6] Therefore, the reaction time was prolonged to
1.5 h, so as to ensure the complete conversion of the inter-
mediate helicene into the dimeric species (6).
High-resolution mass spectrometry (HRMS (ESI): m/z
calcd for C86H92N2O2P2: 1247.6712; found: 1247.6749) and
NMR spectroscopy of compound 6 showed diagnostic sig-
nals of a head-to-head dimeric structure. In the 1H NMR
spectrum, the cyclobutane unit was assigned from the signal
at d=3.05 ppm (dd, J
cyclobutane carbon atoms were assigned from signals in the
13C NMR spectrum at d=36.7 (d, J
(C,P)=48.9 Hz) and
53.8 ppm (s). We couldn’t obtain crystals of compound 6
suitable for X-ray diffraction studies, however, based on our
ACHUTGTNREN(UNG H,P)=29.0 Hz, JHCATUNGTREN(NUGN H,H)=5.5 Hz). The
Scheme 2. Synthesis of compound (RP)-5 as a phosphindole-functional-
ized, stilbene-type substrate for photocyclization reactions. i) I2, propy-
AHCTUNGTRENNUNG
lene oxide, toluene/THF (8:2), hn 150 W, 5 h, 73%; ii) [Pd
(10 mol%), Na2CO3, H2O/toluene/EtOH, 858C, 2.5 h, 46%; iii) [PdCl2-
(SPhos)2] (10 mol%), Cs2CO3,THF/H2O, 85 8C, 18 h, 75%.
ACHTUNGTRNE(NUNG PPh3)4]
G
9940
www.chemeurj.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 9939 – 9947

Heterohelicenes with Embedded Chiral P Units
FULL PAPER
previous work and additional studies (see below), we can
reasonably expect that the RP configuration of the phospho-
rus atom will induce a P helical configuration in the photo-
dehydrogenation reaction. The assumed stereochemistry of
compound 6 is shown in Scheme 3. The dextrorotatory spe-
cific rotation value ([a]D =+1846 (c=0.5, CHCl3)) supports
this assignment.
Overall, these results demonstrate that similar reaction se-
quences take place for both simple polyaromatic and hetero-
aromatic substrates under photochemical conditions. Inter-
estingly, in both cases, the [2+2] cycloaddition reactions of
the phosphole moieties give access to unprecedented bis-
helical structures.
um fluoride (TBAF). Both oxides 7’a (R=Ph) and 7’b (R=
l-menthyl) were obtained in 75% total yield over three
steps. Their hydroxy groups were converted into triflates
(compounds 7a,b) by treatment with PhNTf2.
For R =l-menthyl, the dibenzophosphole oxide, 7’b, was
obtained as a mixture of two epimers with opposite configu-
rations at the stereogenic phosphorus center. The mixture
was converted into triflate 7b and the two diastereomers,
(SP)-7b ([a]D =À48 (c=1, CHCl3); 31P NMR (CDCl3): d=
49.8 ppm) and (RP)-7b ([a]D =À49 (c=1, CHCl3); 31P NMR
(CDCl3): d=49.6 ppm), were separated by HPLC (Merck
NW50 column; heptane/EtOAc, 50:50 to 15:85; retention
times: 11.9 min for (SP)-7b, 13.4 min for (RP)-7b).[17]
However, this dimerization reaction might also represent
a drawback in terms of synthetic efficiency if simple, mono-
meric helical derivatives are targeted. Because dimerization
relates to the high reactivity of the olefinic bond of the
phosphindole, an easy strategy to circumvent this drawback
would be the use of dibenzophospholes as structural units
instead of 1H-phosphindoles, provided that the same reac-
tion sequence could be applied. Therefore, we envisioned
preparing new analogues of olefins I (Scheme 1), in which
the 1H-phosphindol-5-yl unit would be replaced by a diben-
zophosphol-2-yl unit, and using these substrates as starting
materials in the photocyclization reactions. The following
experiments validate this new strategy.
Next, the triflates of dibenzophosphole oxides 7a, (SP)-
7b, and (RP)-7b were submitted to Suzuki coupling reac-
tions with the benzophenanthrene-substituted olefinic boro-
nate 3’ (Scheme 5). The coupling reactions were performed
Our first step in this work was the synthesis of suitable di-
benzophosphole triflates (7; see Scheme 4) and their conver-
sion into the desired olefinic substrates (8) by Suzuki cou-
pling reactions (Scheme 5).
A
variety of dibenzo-
ACHTUNGTRENNUNG[b,d]phospholes are known to be easily available from the
reactions of phosphorus dihalides with o,o’-dilithiated biaryl
compounds.[15] This method also performs very well for the
preparation of 2-hydroxy-substituted dibenzophosphole
Scheme 5. Synthesis of [6]- and [8]helicenes that contain dibenzo
ACHTUNGTRENNUNGphos-
A
CHTUNGTRENNUNG
6 h; ii) I2, propylene oxide, cyclohexane/THF, RT, hn 80 min, crude NMR
ratios: 9a:10a = 70:30; (RP,M)-9b: (RP,P)-10b = 54:46.
in the presence of [PdCl2ACTHNUTRGNE(UGN SPhos)2] (SPhos=2-dicyclohexyl-
phosphino-2’,6’-dimethoxybiphenyl) as the catalyst under
standard conditions. The desired olefinic derivatives 8a
(31P NMR (CDCl3): d=33 ppm), (SP)-8b ([a]D =À168 (c=
0.3, CHCl3); 31P NMR (CDCl3): d=51.0 ppm), and (RP)-8b
([a]D =+207 (c=1, CHCl3); 31P NMR (CDCl3): d=
51.2 ppm) were obtained in high yields (78–87%).
With these new olefinic substrates in hand, next, we inves-
tigated the oxidative photocyclization reactions, as shown in
Scheme 5. In principle, the photocyclization reactions of ole-
fins 8, which combine two non-symmetrical benzophenan-
threne and dibenzophosphole substituents, would afford
either [6]-or [8]helicenes, depending on the carbon atoms
that are involved in the photocyclization process. The link-
ing of C atoms a’ and b would give [6]helicenes, whereas the
linking of C atoms a and b would afford [8]helicenes. Non-
Scheme 4. Synthesis of dibenzo
RT, 18 h, 72 %; ii) tBuMe2SiCl, imidazole, DMF, RT, 4 h, 92%; iii) [Pd-
(PPh3)4] (5%), Na2CO3, toluene/EtOH/H2O (6:2:2), 858C, 6 h, 79%; iv)
ACHTUNGRTEN[NUNG b,d]phosphole oxides 7a,b. i) Br2, AcOH,
ACHTUNGTRENNUNG
a) tBuLi, ether, À788C to RT, 18 h; b) H2O2, CH2Cl2, 10 min; c) TBAF
(1m, THF), 30 min; v) Cs2CO3, DMF, RT, 18 h.
oxides (7’; Scheme 4). After bromine/lithium exchange on
the dibromobiphenyl derivative shown in Scheme 4, the di-
ACHTUNGTRENNUNGlithACHTUNGTRENNUNGiACHTUNGTRENNUNGated intermediate was treated with either PhPCl2 or (l-
menthyl)PCl2.[16] The resulting dibenzophospholes were oxi-
dized in situ with H2O2 and the tert-butyldimethylsilyl (TBS)
group was removed by reaction with tetra-n-butylammoni-
Chem. Eur. J. 2013, 19, 9939 – 9947
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9941

A. Voituriez, A. Marinetti et al.
helical compounds might also be produced[7b,18] if C atom b’
is involved in the cyclization process.
The oxidative photocyclization of compound 8a (R=Ph)
in cyclohexane/THF with a 150 W mercury lamp afforded a
mixture of [6]- and [8]helicenes 9a and 10a in a 7:3 ratio, to-
gether with <10% of a side product that we tentatively as-
signed as a non-helical cyclodehydrogenation product. Both
compounds 9a and 10a have been isolated in their pure
forms and characterized by X-ray diffraction studies. The
ORTEPs of these structures are shown in Figure 2 and
Figure 3, respectively. The X-ray data show that, for both
compounds, the phenyl substituent on the phosphorus atom
is oriented toward the polyaromatic scaffold, thus giving a
RP*,M* relative configuration for compound 9a and a
RP*,P* relative configuration for compound 10a.
Figure 4. Columnar packing of crystals of (RP*,P*)-10a that were grown
from a saturated solution in CDCl3. Crystal system: triclinic; space
¯
group: P1.
Overall, the outcome of the oxidative photocyclization of
8a (Scheme 5) confirms the general trend by which the
phosphorus configuration controls the sense of helical chir-
ality.[19] This trend results in the formation of a single dia-
stereomer for each of helical the species 9a and 10a.
Comparable, very high diastereoselectivity was also ob-
served in the photocyclodehydrogenation of the P-menthyl-
substituted substrate (RP)-8b (Scheme 5). The expected
[6]helicene, (RP,M)-9b, and [8]helicene, (RP,P)-10b, were
obtained in a 54:46 ratio (61% total yield) and were sepa-
1
rated by HPLC. For compound (RP,P)-10, the H NMR data
were diagnostic of a [8]helicene structure, with a characteris-
tic high-field shift of the H-5 signal at d=5.44 ppm (dd, J-
Figure 2. ORTEP of [6]helicene (RP*,M*)-9a; thermal ellipsoids are set
ACHUTNGERN(NUG H,H)=8.1 Hz, JCAHTUNGTRNE(NUGN H,P)=3.3 Hz; for the atom numbering,
at 30% probability. Selected distances and angles are given in Table 1.
see Scheme 5). These helical compounds were isolated as
single diastereomers. They were also enantiomerically pure,
owing to the use of a single epimer of 7b as the starting ma-
terial in this reaction sequence. This result highlights one of
the major advantages of our synthetic method: The use of
an l-menthyl substituted dibenzophosphole as the starting
material, combined with the excellent control over helicity
in the photocyclization step (diastereoselectivity), gives
access to enantiomerically pure derivatives whilst avoiding
the need for difficult and expensive separation by chiral
HPLC.
[6]helicene (RP,M)-9b and phospha[8]helicene (RP,P)-10b
display opposite optical rotation values, thus suggesting a
prevalence of the helical chirality effects over central chirali-
ty effects in determining their chiroptical properties: [a]D =
À2367 (c=0.5, CHCl3) for compound (RP,M)-9b and [a]D =
+2048 (c=0.5, CHCl3) for compound (RP,P)-10b. CD spec-
tra for compounds (RP,M)-9b and (RP,P)-10b are given in
Figure 5.
Interestingly, the photochemical cyclization experiments
shown in Scheme 5 highlight a divergent behavior between
the two epimeric olefins, (RP)-8b and (SP)-8b, with respect
to the chemoselectivity of the reaction. Indeed, unlike com-
pound (RP)-8b, the olefinic substrate (SP)-8b mainly afford-
ed [6]helicene (SP,P)-9b ([a]D =+2394 (c=0.7, CHCl3);
31P NMR (CDCl3): d=51 ppm). The corresponding [8]heli-
cene was observed in <2% yield and could not be isolated
in its pure form. The divergent behavior of the two epimers
Figure 3. ORTEP of phospha[8]helicene (RP*,P*)-10a; thermal ellipsoids
are set at 50% probability. Selected distances and angles are given in
Table 1.
Compound (RP*,P*)-10a is the first example of a phos-
pha[8]helicene reported to date. The structural features of
compound (RP*,P*)-10a and, in particular, the environment
around the phosphorus center differ significantly from that
of compound (RP*,M*)-9a, in as far as the phosphorus atom
in compound 9a overhangs the internal rim of the polyaro-
matic sequence, whereas that in compound 10a is located on
the external edge of the helical structure.
In the solid state, [8]helicene 10a displays a columnar ar-
rangement of homochiral units:[5] Each column, which is
made up of a single enantiomer, alternates with columns
that are made up of the opposite enantiomer, as shown in
Figure 4.
9942
www.chemeurj.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 9939 – 9947

Heterohelicenes with Embedded Chiral P Units
FULL PAPER
Scheme 6. Synthesis of helical phosphine sulfide (RP,M)-12. i) Lawesson’s
reagent, toluene, RT, overnight 79%; ii) I2, propylene oxide, cyclohexane/
THF, hn 80 min, 50%.
Figure 5. CD spectra of a) (RP,M)-9b (1.0ꢁ10À5
b) (RP,P)-10b (1.5ꢁ10À5 m in CH2Cl2).
m in CH2Cl2) and
same overall spatial arrangement as that previously found in
the corresponding oxide, (RP,M)-9b, with an R configuration
at the phosphorus atom, combined with an M helical config-
uration (selected X-ray date are given in Table 1; for the
ORTEP, see the Supporting Information).
of compound 8b further supports the key role of the stereo-
genic phosphorus atom in these photocyclization reactions.
Compound (SP,P)-9b was characterized by X-ray diffrac-
tion studies (Figure 6). The X-ray data confirm its molecular
structure, as well as the relative configurations of the central
and helical chirality elements: Beside the l-menthyl frag-
ment, the molecule displays an S-configured phosphorus
atom and a P-configured helical scaffold.
Overall, the synthetic studies discussed above demon-
strate the reliability and versatility of our approach towards
a new class of phosphorus-containing helicenes. As already
mentioned in the Introduction section of this paper, one of
the main assets related to the presence of a phosphorus
group is the potential of coordinating it to transition metals
for both structural tuning and catalytic applications. For
such purposes, we have performed a preliminary investiga-
tion into the coordinating behavior of the trivalent phospha-
helicenes that are available from oxides 9 and 10. As shown
hereafter, these helicenes were combined with gold(I) and
iridium(I) complexes to check their suitability to form com-
plexes with various coordination numbers and geometrical
constraints.
The reduction of phosphine oxide (RP*,M*)-9a with
HSiCl3/Et3N produced the corresponding trivalent phos-
phine (31P NMR (CDCl3): d=À9 ppm), which was reacted,
without further purification, with
a
mixture of
NaAuCl4·2H2O and 2,2’-thiodiethanol as the gold-reducing
agent. This procedure afforded the gold chloride complex
(RP*,M*)-13 as a yellow powder in 46% yield. The P-
menthyl-substituted [6]helicene (RP,P)-10b was reduced
under analogous conditions (31P NMR (CDCl3): d=À5 ppm
for the corresponding trivalent phosphine and reacted with
[{(cod)IrCl}2] (cod=1,5-cyclooctadiene) to give compound
14 as a red powder in 37% yield (Scheme 7; [a]D =+1426
(c=0.4, CHCl3)).
In both reactions, the desired complexes were produced
as mixtures of two isomers in >9:1 ratios. The X-ray crystal
structure of the gold-chloride complex 13 shows that the
gold atom is located on the less-hindered external face of
the helical structure, whereas the phenyl substituent on the
phosphorus group is oriented toward the helical scaffold
(Figure 7). This substitution pattern results in a relative
RP*,M* configuration for compound 13, that is, the phospho-
rus center retains the overall arrangement of its phosphine-
oxide precursor, (RP*,M*)-9a. To account for this selectivity,
we postulate that both the reduction and complexation steps
occur with retention of the configuration at the phosphorus
Figure 6. ORTEP of [6]helicene (SP,P)-9b; thermal ellipsoids are set at
30% probability. Selected distances and angles are given in Table 1.
As mentioned above, all of the photocyclization experi-
ments performed so far display a marked selectivity in favor
of the helical phosphine oxides in which the phosphorus
substituent (phenyl or menthyl groups) is oriented toward
the helical scaffold. This preference seems not to be related
to the presence of a phosphine-oxide group, because it has
also been observed in the photocyclization of phosphine sul-
fide (RP)-11 (Scheme 6). This sulfide was prepared in 79%
yield from the corresponding oxide by using the Lawesson
reagent. The photolysis of compound (RP)-11 afforded com-
pound (RP,M)-12 as the major product (isolated in 50%
1
yield). H NMR analysis of the crude reaction mixture only
showed the presence of small amounts of the corresponding
[8]helicene (approximate 15:85 ratio to compound 12). The
phosphine sulfide (RP,M)-12 was characterized by X-ray dif-
fraction studies. X-ray data show that compound 12 has the
Chem. Eur. J. 2013, 19, 9939 – 9947
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9943

A. Voituriez, A. Marinetti et al.
Table 1. Selected distances [ꢂ] and angles [8] from X-ray diffraction analysis of helical
derivatives 10a, 9a, (SP,P)-9b, (RP,M)-12, and 13.[a]
bonds) form dihedral angles with the phosphole
rings of between 1118 and 1198, with the smallest
angle (i.e., the more-pronounced pyramidal ar-
rangement of the P substituents) being observed in
gold complex 13.
Overall, our preliminary investigations on the co-
ordination chemistry of phosphahelicenes, as sum-
marized in Scheme 7, show that both the [6]- and
[8]helicene scaffolds, in spite of their substantially
different geometries and spatial arrangements of
the phosphorus centers, afford ligands that are suit-
able for coordinating to transition metals. This
result opens up new possibilities, notably in the
field of phosphine-based asymmetric organometallic
catalysis, in which the potential of helical chirality
has largely been neglected so far.[3b,c,h,22]
10a
1.488(2)
9a
1.493(3)
G
(RP,M)-12
13
À
À
À
P O/P S/P Au
À
P C1
2.2229(16)
1.799(6)
1.804(5)
1.819(6)
1.421(7)
1.468(7)
1.427(6)
1.793(4)
1.785(4)
1.791(4)
1.416(4)
1.496(5)
1.399(5)
92.00(16)
109.24(16) 110.3(2)
3.256
116.88
1.795(5)
1.795(5)
1.787(5)
1.393(7)
1.494(7)
1.418(6)
92.4(3)
À
P C8
À
P C10
À
C1 C6
À
C6 C7
À
C7 C8
C1-P-C8
92.4(3)
107.2(3)
3.101
Conclusion
C8-P-C10
[b]
À
C7/9 C9’
3.129
119.3
C10-P-C6/7[c]
111.40
In summary, this work demonstrates that the oxida-
tive photocyclization reactions of diarylolefins that
feature P-chiral 1H-phosphindole or dibenzophosp-
À
À
[a] 10a: PhP(O) [8]helicene; 9a: PhP(O) [6]helicene; 9b: Men*P(O) [6]helicene;
À
12: Men*P(S) [6]helicene; 13: PhPACTHNUGRTENUNG(AuCl) [6]helicene. CCDC-921789 (10a), CCDC-
921788 (9a), CCDC-921787 (9b), CCDC-921790 (12), and CCDC-921791 (13) contain hole units afford simple and versatile access to heli-
the supplementary crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.ca-
m.ac.uk/data_request/cif. [b] Calculated helical pitch. [c] C6/7=centroid of the C6 C7
cal derivatives with embedded phosphorus groups
in the polyaromatic scaffolds. The photocyclization
step is highly diastereoselective because the stereo-
À
bond.
genic phosphorus center plays a key role in control-
Scheme 7. Synthesis of gold (13) and iridium complexes (14) of [6]- and
[8]helicenes. i) HSiCl3, Et3N, toluene, RT, 1–3 h; ii) 2,2’-thiodiethanol,
CHCl3/H2O (1:5), 08C to RT, overnight.
center, because dibenzophospholes are reported to be con-
figurationally stable at room temperature for at least several
hours (t1/2 =19–338 h).[20,21]
For comparison, selected X-ray data for complex 13 are
listed in Table 1, together with X-ray data for compounds
10a, 9a, (SP,P)-9b, and (RP,M)-12. In these structures, the
helical pitch goes from 2.987 ꢂ (for [6]helicene sulfide
(RP,M)-12) to a maximum of 3.256 ꢂ (for [8]helicene oxide
Figure 7. ORTEP (a) and a Mercury view (b) of gold complex 13; ther-
À
À
À
10a). The exocyclic P C bonds (P phenyl or P menthyl
mal ellipsoids are set at 50% probability.
9944
www.chemeurj.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 9939 – 9947

Heterohelicenes with Embedded Chiral P Units
FULL PAPER
(CH), 123.7 (d, J=9.5 Hz, CH), 120.9 (d, J=9.2 Hz, CH), 43.9 (CH), 40.8
(d, J=66.9 Hz, CH), 36.8 (CH2), 36.0 (CH2), 34.8 (CH2), 33.3 (CH2), 32.3
(d, J=14.5 Hz, CH), 29.5 (CH), 24.7 (d, J=13.2 Hz, CH2), 21.9 (CH2),
21.6 (CH2), 21.4 (CH3), 21.3 (CH3), 15.9 (CH3), 14.2 (CH3), 14.1 ppm
(CH3); 31P NMR (125 MHz, CDCl3): d=51 ppm; HRMS (ESI): m/z calcd
for C48H52OP: 675.3756 [M+H]+; found: 675.3764.
ling the helicity. As a consequence, starting from single epi-
mers of optically pure P-menthyl-substituted substrates, the
method affords optically pure species, whilst avoiding scale-
up-limiting and expensive chiral HPLC separations. P/N-di-
hetero[6]helicene derivatives, as well as [6]- and [8]heli-
cenes, with P(O) groups have been isolated in their enantio-
merically pure form by using this method. The reduction of
the phosphine oxides into trivalent phosphines and subse-
quent complexation demonstrate that both the [6]- and
[8]helicenes are able to coordinate transition metals, thereby
leading to the first known gold and iridium complexes of
helical phosphines of this class. The phosphorus configura-
tion is retained throughout this process. These experiments
anticipate the possible use of helicenes with embedded
cyclic phosphorus units as chiral ligands in enantioselective
catalysis.
Photochemical oxidative cyclization of compound (RP)-8b: To a solution
of compound (RP)-8b (0.1 mmol, 67 mg) in THF (25 mL) were added
iodine (0.2 mmol, 54 mg), propylene oxide (10 mmol, 0.7 mL), and cyclo-
hexane (350 mL). The mixture was irradiated for 1 h 20 min (Heraeus
TQ, 150 Watt). After removal of the solvent, the crude mixture was puri-
fied by column chromatography on silica gel (CH2Cl2/EtOH, 98:2) to
afford a mixture of compounds (RP,M)-9b and (RP,P)-10b (54:46), as
well as a small amount of an unidentified side product. From this mix-
ture, compound (RP,P)-10b was isolated in 31% yield. Compound
(RP,M)-9b was purified by HPLC (Waters Sunfire C18 OBD, 5 mm,
MeCN/H2O/CHCOOH) and isolated in 30% yield.
A
CHCl3); 1H NMR (300 MHz, CDCl3): d=8.34 (d, J=2.1 Hz, 1H), 8.12
(d, J=8.7 Hz, 1H), 8.08–7.93 (m, 5H), 7.91–7.82 (m, 2H), 7.76 (d, J=
7.8 Hz, 1H), 7.64–7.47 (m, 3H), 7.32 (td, J=7.5, 3.3 Hz, 1H), 7.16 (t, J=
7.5 Hz, 1H), 6.80–6.72 (m, 1H), 3.42–3.25 (m, 4H), 2.62–2.51 (m, 1H),
2.20–1.65 (m, 7H), 1.30–1.20 (m, 6H), 1.18–0.95 (m, 3H), 0.90–0.75 (m,
2H), 0.80 (d, J=6.9 Hz, 3H), 0.72 (d, J=6.9 Hz, 3H), 0.66 (d, J=5.4 Hz,
3H), À0.20 ppm (m, 1H); 13C NMR (75 MHz, CDCl3): d=162.7 (C),
142.3 (d, J=17.1 Hz, C), 138.5 (d, J=18.9 Hz, C), 136.3 (C), 134.8 (C),
133.8 (d, J=99.8 Hz, C), 133.6 (C), 132.7 (CH), 132.6 (C), 132.4 (C),
131.9 (d, J=11.4 Hz, C), 131.7 (C), 131.6 (d, J=10.4 Hz, CH), 130.7 (C),
129.2 (C), 129.03 (d, J=10.5 Hz, CH), 129.01 (CH), 128.9 (C), 128.4 (C),
128.3 (d, J=9.2 Hz, CH), 128.1 (CH), 127.9 (CH), 127.7 (CH), 127.33
(CH), 128.28 (CH), 126.5 (CH), 125.7 (CH), 125.1 (CH), 123.9 (C), 123.1
(CH), 121.1 (d, J=9.0 Hz, CH), 116.6 (d, J=8.9 Hz, CH), 43.2 (d, J=
3.1 Hz, CH), 40.3 (d, J=67.2 Hz, CH), 34.0 (CH2), 33.7 (CH2), 33.0 (d,
J=15.6 Hz, CH), 31.9 (CH2), 31.3 (CH2), 28.8 (CH), 25.4 (d, J=13.5 Hz,
CH2), 24.9 (CH2), 24.5 (CH2), 22.3 (CH3), 21.4 (CH3), 16.2 (CH3), 14.9
(CH3), 14.7 ppm (CH3); 31P NMR (125 MHz, CDCl3): d=52 ppm; HRMS
(ESI): m/z calcd for C48H50OP: 673.3599 [M+H]+; found: 673.3602.
Experimental Section
General methods: All of the reactions were performed under an inert
argon atmosphere by using standard techniques for manipulating air-sen-
sitive compounds. All glassware was stored in the oven and/or flame-
dried prior to use. Anhydrous solvents (THF, Et2O, CH2Cl2) were ob-
tained by filtration through drying columns. All reagents and solvents
were of commercial grade and used without further purification. Purifica-
tions were performed on a CombiFlash Companion TS Chromatography
system on silica gel columns. NMR spectroscopy (1H, 13C, 31P) was per-
formed on Brucker AV 500 or AV 300 spectrometers. IR spectra were re-
corded on a Perkin–Elmer FTIR spectrophotometer. High-resolution
mass spectroscopy (ESI) was performed on LCT Waters equipment. Op-
tical rotations were determined on a JASCO P-1010 polarimeter. HPLC
was performed at a column temperature of 208C on a Waters 2695 Sepa-
rations Module that was equipped with a diode-array UV detector. Pho-
tocyclization experiments were performed on a Heraeus TQ with a 150
Watt immersion lamp.
AHCTUNGTRENNUNG
(RP,P)-10b: Rf =0.32 (EtOH/CH2Cl2, 1:24); [a]2D5 =+2048 (c=0.5,
CHCl3); 1H NMR (300 MHz, CDCl3): d=8.29 (d, J=8.7 Hz, 1H), 8.13
(d, J=8.4 Hz, 1H), 8.01 (dd, J=8.4, 3.3 Hz, 1H), 7.97 (d, J=8.4 Hz, 1H),
7.74 (d, J=8.1 Hz, 1H), 7.65–7.56 (m, 2H), 7.48–7.38 (m, 2H), 7.34 (t,
J=8.4 Hz, 1H), 7.06 (m, 1H), 6.91 (d, J=8.4 Hz, 1H), 6.82 (dd, J=7.2,
3.0 Hz, 1H), 6.58 (m, 1H), 6.39 (t, J=7.8 Hz, 1H), 5.44 (dd, J=8.1,
3.3 Hz, 1H), 3.37–3.26 (m, 4H), 2.50–2.36 (m, 1H), 2.00–1.70 (m, 7H),
1.65–1.45 (m, 2H), 1.27 (t, J=7.2 Hz, 3H), 1.22 (t, J=7.2 Hz, 3H), 1.25–
1.00 (m, 4H), 1.08 (d, J=6.6 Hz, 3H), 0.98 (d, J=5.4 Hz, 3H), 0.71 ppm
(d, J=6.9 Hz, 3H); 13C NMR (75 MHz, CDCl3): d=143.6 (d, J=21.2 Hz,
C), 140.2 (d, J=20.2 Hz, C), 135.9 (C), 135.6 (C), 134.7 (d, J=2.2 Hz, C),
133.8 (d, J=57.2 Hz, C), 132.5 (d, J=51.6 Hz, C), 131.7 (C), 131.3 (C),
131.1 (C), 130.3 (d, J=1.9 Hz, CH), 129.7 (J=9.3 Hz, CH), 128.8 (C),
128.7 (C), 127.53 (CH), 127.49 (C), 127.35 (J=8.1 Hz, CH), 127.33 (CH),
127.30 (CH), 127.26 (CH), 126.9 (d, J=10.8 Hz, C), 126.8 (d, J=10.3 Hz,
CH), 126.5 (CH), 125.9 (CH), 125.3 (CH), 124.8 (C), 124.3 (CH), 123.2
(d, J=10.0 Hz, CH), 123.1 (CH), 122.1 (d, J=9.2 Hz, CH), 42.3 (J=
3.4 Hz, CH), 41.6 (d, J=68.1 Hz, CH), 37.6 (d, J=3.2 Hz, CH), 34.1
(CH2), 32.9 (d, J=13.1 Hz, CH), 31.9 (CH2), 30.3 (J=2.4 Hz, CH), 24.8
(CH2), 24.6 (CH2), 24.4 (J=16.3 Hz, CH2), 22.4 (CH3), 22.0 (CH3), 16.1
(CH3), 15.0 (CH3), 14.9 ppm (CH3); 31P NMR (125 MHz, CDCl3): d=
49 ppm; HRMS (ESI): m/z calcd for C48H50OP: 673.3599 [M+H]+;
found: 673.3608.
(5R)-2-((Z)-5-(Benzo[c]phenanthren-2-yl)oct-4-en-4-yl)-5-((1S,2R,5S)-2-
isopropyl-5-methylcyclohexyl)-5H-benzo[b]phosphindole 5-oxide, (RP)-
8b: To a mixture of triflate (RP)-7b (2.25 mmol, 1.1 g) and (E)-2-(5-(ben-
zo[c]phenanthren-2-yl)oct-4-en-4-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lane (3.4 mmol, 1.58 g) in THF (34 mL) were added Cs2CO3 (6.2 mmol,
2.0 g), [PdCl2ACHTUNGTRENNUNG(SPhos)2] (0.45 mmol, 230 mg), and degassed water
(3.5 mL). The reaction mixture was stirred for 18 h at 858C. The mixture
was extracted with EtOAc and the extract washed with water and brine,
dried over MgSO4, and concentrated in vacuo. The residue was purified
by flash chromatography on silica gel (heptane/acetone, 1:0 to 3:2) to
afford the desired product as a pale-yellowish powder (1.33 g, 87%
yield). Rf =0.2 (EtOAc/heptanes, 1:1); [a]2D5 =+207 (c=1.0, CHCl3);
1H NMR (500 MHz, CDCl3): d=8.59 (s, 1H), 8.14 (d, J=8.0 Hz, 1H),
7.93 (dd, J=7.5, 2.0 Hz, 1H), 7.85 (d, J=8.0 Hz, 1H), 7.79 (d, J=8.5 Hz,
1H), 7.74 (d, J=8.5 Hz, 1H), 7.71 (d, J=8.5 Hz, 1H), 7.67 (d, J=8.5 Hz,
1H), 7.65–7.55 (m, 2H), 7.53–7.45 (m, 5H), 7.43 (t, J=7.5 Hz, 1H), 7.35
(dd, J=7.5, 2.0 Hz, 1H), 7.29 (dt, J=7.0, 3.0 Hz, 1H), 2.78–2.60 (m, 5H),
2.05–1.95 (m, 1H), 1.50–1.40 (m, 2H), 1.35–1.25 (m, 4H), 1.20–1.10 (m,
1H), 1.05–0.95 (m, 1H), 0.99 (t, J=7.5 Hz, 3H), 0.89 (t, J=7.0 Hz, 3H),
0.84 (d, J=6.5 Hz, 3H), 0.80–0.60 (m, 2H), 0.73 (d, J=6.5 Hz, 3H),
À0.26 (d, J=6.5 Hz, 3H), À0.35 (m, 1H), À0.60 ppm (q, J=11.0 Hz,
1H); 13C NMR (125 MHz, CDCl3): d=149.2 (C), 141.5 (d, J=19.6 Hz,
C), 141.6 (d, J=18.6 Hz, C), 141.3 (C), 141.1 (C), 139.0 (C), 133.5 (C),
132.7 (d, J=98.6 Hz, C), 132.6 (CH), 131.8 (C), 131.2 (C), 130.3 (d, J=
9.2 Hz, CH), 129.9 (C), 129.7 (d, J=9.2 Hz, CH), 129.6 (d, J=93.1 Hz,
C), 129.4 (CH), 129.2 (J=9.1 Hz, CH), 128.9 (d, J=10.6 Hz, CH),128.6
(CH), 128.2 (CH), 128.1 (CH), 127.5 (d, J=42.8 Hz, C), 127.3 (CH),
127.24 (CH), 127.20 (CH), 127.0 (CH), 126.4 (CH), 126.2 (CH), 125.7
Synthesis of gold complex (RP*,M*)-13: To a solution of compound
(RP*,M*)-9a (0.066 mmol, 40 mg) in degased anhydrous toluene (5 mL)
were added Et3N (0.1 mL) and HSiCl3 (0.4 mL). The reaction mixture
was stirred for 1 h before being quenched by a degassed aqueous solution
of 1m NaOH and extracted twice with anhydrous THF under an argon
atmosphere. The mixture was dried with MgSO4 and evaporated under
vacuum. Thiodiglycol (0.2 mmol, 17 mL) was added dropwise to an ice-
cold solution of NaAuCl4·H2O (0.066 mmol, 27 mg) in degased water.
Chem. Eur. J. 2013, 19, 9939 – 9947
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9945

A. Voituriez, A. Marinetti et al.
When the yellow solution had turned colorless, a solution of the phos-
phine in CHCl3 (2 mL) was added at 08C. The mixture was allowed to
stir overnight at room temperature, before being extracted with EtOAc,
washed with water, dried over MgSO4, and concentrated in vacuo. The
residue was purified by flash chromatography on silica gel (CH2Cl2/hep-
tanes, 50:50) to obtain gold complex (RP*,M*)-13 as a yellow powder
Raboso, M. Gꢇmez-Gallego, M. Martꢅn-Ortiz, M. Olivꢆn, M. A.
Sierra, Chem. Commun. 2012, 48, 5328–5330; l) A. Latorre, A.
Urbano, M. C. Carreno, Chem. Commun. 2011, 47, 8103–8105.
[3] For examples of helical compounds with appended phosphorus
groups and their transition-metal complexes, see: a) A. Terfort, H.
Gçrls, H. Brunner, Synthesis 1997, 79–86; b) M. T. Reetz, E. W.
Beuttenmꢈller, R. Goddard, Tetrahedron Lett. 1997, 38, 3211–3214;
c) M. T. Reetz, S. Sostmann, J. Organomet. Chem. 2000, 603, 105–
109; d) D. J. Weix, S. D. Dreher, T. J. Katz, J. Am. Chem. Soc. 2000,
1
(25 mg, 46% yield). H NMR (500 MHz, CDCl3): d=8.50 (br s, 1H), 8.15
(d, J=8.0 Hz, 1H), 8.05–7.96 (m, 4H), 7.90 (d, J=12.5 Hz, 1H), 7.83 (d,
J=8.5 Hz, 1H), 7.65–7.58 (m, 2H), 7.48–7.39 (m, 4H), 7.38–7.28 (m,
2H), 7.13–7.07 (m, 2H), 6.96 (d, J=7.5 Hz, 1H), 6.75 (t, J=7.0 Hz, 1H),
6.52 (t, J=7.5 Hz, 1H), 3.41–3.25 (m, 4H), 1.98–1.85 (m, 4H), 1.32–
1.20 ppm (m, 6H); 13C NMR (75 MHz, CDCl3): d=143.7 (d, J=12.8 Hz,
C), 141.8 (d, J=77.8 Hz, C), 138.3 (d, J=13.9 Hz, C), 136.8 (C), 134.6
(C), 134.2 (CH), 134.0 (CH), 133.03 (C), 132.96 (d, J=67.2 Hz, C), 132.9
(d, J=16.0 Hz, CH), 132.7 (C), 132.32 (d, J=15.0 Hz, CH), 132.28 (d, J=
14.9 Hz, CH), 131.6 (C), 131.4 (C), 131.3 (d, J=13.7 Hz, CH), 130.9 (C),
130.8 (d, J=12.8 Hz, C), 129.7 (CH), 129.5 (CH), 129.1 (d, J=11.6 Hz,
CH), 128.7 (C), 128.5 (d, J=58.6 Hz, C), 128.14 (C), 128.16 (CH), 127.99
(C), 127.82 (CH), 127.79 (CH), 127.7 (CH), 127.66 (d, J=55.4 Hz, C),
127.2 (CH), 126.6 (CH), 126.5 (CH), 124.9 (CH), 124.3 (CH), 123.8 (C),
123.1 (CH), 121.8 (d, J=7.2 Hz, CH), 116.9 (d, J=7.4 Hz, CH), 32.1
(CH2), 31.5 (CH2), 24.8 (CH2), 24.5 (CH2), 14.9 (CH3), 14.8 ppm (CH3);
31P NMR (125 MHz, CDCl3): d=25 ppm.
´
122, 10027–10032; e) K. Paruch, L. Vyklicky, D. Z. Wang, T. J. Katz,
C. Incarvito, L. Zakharov, A. L. Rheingold, J. Org. Chem. 2003, 68,
ˇ
´
´
ˇ
8539–8544; f) F. Teply, I. G. Starꢆ, I. Stary, A. Kollꢆrovic, D. Saman,
ˇ
ˇ
S. Vyskocil, P. Fiedler, J. Org. Chem. 2003, 68, 5193–5197; g) F.
Aloui, R. El Abed, A. Marinetti, B. Ben Hassine, Tetrahedron Lett.
2007, 48, 2017–2020; h) Z. Krausovꢆ, P. Sehnal, B. P. Bondzic, S.
ˇ
´
Chercheja, P. Eilbracht, I. G. Starꢆ, D. Saman, I. Stary, Eur. J. Org.
Chem. 2011, 3849–3857.
[4] a) N. Fukawa, T. Osaka, K. Noguchi, K. Tanaka, Org. Lett. 2010, 12,
1324–1327; b) Y. Sawada, S. Furumi, A. Takai, M. Takeuchi, K. No-
guchi, K. Tanaka, J. Am. Chem. Soc. 2012, 134, 4080–4083.
[5] K. Nakano, H. Oyama, Y. Nishimura, S. Nakasako, K. Nozaki,
Angew. Chem. 2012, 124, 719–723; Angew. Chem. Int. Ed. 2012, 51,
695–699.
[6] K. Yavari, S. Moussa, B. Ben Hassine, P. Retailleau, A. Voituriez, A.
Marinetti, Angew. Chem. 2012, 124, 6852–6856; Angew. Chem. Int.
Ed. 2012, 51, 6748–6752.
[7] a) M. Flammang-Barbieux, J. Nasielski, R. H. Martin, Tetrahedron
Lett. 1967, 8, 743–744; b) F. B. Mallory, C. W. Mallory, in Organic
Reactions, Vol. 30 (Ed.: W. G. Dauben), Wiley, New York, 1984;
c) L. Liu, B. Yang, T. J. Katz, M. K. Poindexter, J. Org. Chem. 1991,
56, 3769–3775.
[8] R. H. Martin, M. Deblecker, Tetrahedron Lett. 1969, 10, 3597–3598.
[9] a) N. Takenaka, R. S. Sarangthem, B. Captain, Angew. Chem. 2008,
120, 9854–9856; Angew. Chem. Int. Ed. 2008, 47, 9708–9710; b) J.
Chen, N. Takenaka, Chem. Eur. J. 2009, 15, 7268–7276; c) N. Taken-
aka, J. Chen, B. Captain, R. S. Sarangthem, A. Chandrakumar, J.
Am. Chem. Soc. 2010, 132, 4536–4537; d) J. Chen, B. Captain, N.
Takenaka, Org. Lett. 2011, 13, 1654–1657; e) M. R. Crittall, H. S.
Rzepa, D. R. Carbery, Org. Lett. 2011, 13, 1250–1253.
[10] For representative examples, see: a) K. Ohmatsu, M. Ito, T. Kunie-
da, T. Ooi, Nat. Chem. 2012, 4, 473–477; b) J.-B. Xie, J.-H. Xie, X.-
Y. Liu, W.-L. Kong, S. Li, Q.-L. Zhou, J. Am. Chem. Soc. 2010, 132,
4538–4539; c) D. W. Old, J. P. Wolfe, S. L. Buchwald, J. Am. Chem.
Soc. 1998, 120, 9722–9723; d) S. Rousseaux, J. Garcꢅa-Fortanet,
M. A. Del Aguila Sanchez, S. L. Buchwald, J. Am. Chem. Soc. 2011,
133, 9282–9285; e) S. Takizawa, T. M.-N. Nguyen, A. Grossmann, D.
Enders, H. Sasai, Angew. Chem. 2012, 124, 5519–5522; Angew.
Chem. Int. Ed. 2012, 51, 5423–5426; Angew. Chem. Int. Ed. 2012,
51, 5423–5426; f) T. Hayashi, M. Konishi, H. Ito, M. Kumada, J.
Am. Chem. Soc. 1982, 104, 4962–4963; g) R. Bellini, J. N. H. Reek,
Chem. Eur. J. 2012, 18, 13510–13519; h) B. Tao, G. C. Fu, Angew.
Chem. 2002, 114, 4048–4050; Angew. Chem. Int. Ed. 2002, 41, 3892–
3894; i) G. Helmchen, A. Pfaltz, Acc. Chem. Res. 2000, 33, 336–345;
j) A. I. Aranda Perez, T. Biet, S. Graule, T. Agou, C. Lescop, N. R.
Branda, J. Crassous, R. Rꢃau, Chem. Eur. J. 2011, 17, 1337–1351.
[11] a) S. Graule, M. Rudolph, N. Vanthuyne, J. Autschbach, C. Roussel,
J. Crassous, R. Rꢃau, J. Am. Chem. Soc. 2009, 131, 3183–3185; b) S.
Graule, M. Rudolph, W. Shen, J. A. G. Williams, C. Lescop, J.
Autschbach, J. Crassous, R. Rꢃau, Chem. Eur. J. 2010, 16, 5976–
6005; c) V. Vreshch, M. El Sayed Moussa, B. Nohra, M. Srebro, N.
Vanthuyne, C. Roussel, J. Autschbach, J. Crassous, C. Lescop, R.
Rꢃau, Angew. Chem. 2013, 125, 2022–2026; Angew. Chem. Int. Ed.
2013, 52, 1968–1972.
Acknowledgements
The authors thank the ICSN for a grant (to K.Y.) and the Cost Action
PhoSciNet (CM0802) for supporting this work. The authors thank Dr
Jeanne Crassous (Universitꢃ de Rennes I, UMR 6226) for her helpful
discussions and Ms Mathilde Belnou for her involvement in the experi-
mental work..
[1] a) Y. Shen, C.-F. Chen, Chem. Rev. 2012, 112, 1463–1535; b) M.
Gingras, Chem. Soc. Rev. 2013, 42, 968–1006; c) M. Gingras, G.
Fꢃlix, R. Peresutti, Chem. Soc. Rev. 2013, 42, 1007–1050; d) M.
Gingras, Chem. Soc. Rev. 2013, 42, 1051–1095; e) A. Urbano, M. C.
Carreno, Org. Biomol. Chem. 2013, 11, 699–708; f) T. J. Katz,
Angew. Chem. 2000, 112, 1997–1999; Angew. Chem. Int. Ed. 2000,
39, 1921–1923; g) A. Urbano, Angew. Chem. 2003, 115, 4116–4119;
Angew. Chem. Int. Ed. 2003, 42, 3986–3989; h) R. H. Martin,
Angew. Chem. 1974, 86, 727–738; Angew. Chem. Int. Ed. Engl.
1974, 13, 649–660; i) W. H. Laarhoven, W. J. C. Prinsen, Top. Curr.
Chem. 1984, 125, 63–130; j) W. H. Meurer, F. Vogtle, Top. Curr.
Chem. 1985, 127, 1–76.
[2] For examples of helical structures that are comprised of, or tuned
by, transition metals, see: a) T. J. Katz, J. Pesti, J. Am. Chem. Soc.
1982, 104, 346–347; b) A. Sudhakar, T. J. Katz, J. Am. Chem. Soc.
1986, 108, 179–181; c) A. M. Gilbert, T. J. Katz, W. E. Geiger, M. P.
Robben, A. L. Rheingold, J. Am. Chem. Soc. 1993, 115, 3199–3211;
d) T. J. Katz, A. Sudhakar, M. F. Teasley, A. M. Gilbert, W. E.
Geiger, M. P. Robben, M. Wuensch, M. D. Ward, J. Am. Chem. Soc.
1993, 115, 3182–3198; e) A. Latorre, A. Urbano, M. C. CarreÇo,
Chem. Commun. 2009, 6652–6654; f) L. Norel, M. Rudolph, N. Van-
thuyne, J. A. G. Williams, C. Lescop, C. Roussel, J. Autschbach, J.
Crassous, R. Rꢃau, Angew. Chem. 2010, 122, 103–106; Angew.
Chem. Int. Ed. 2010, 49, 99–102; g) E. Anger, M. Rudolph, C. Shen,
N. Vanthuyne, L. Toupet, C. Roussel, J. Autschbach, J. Crassous, R.
Rꢃau, J. Am. Chem. Soc. 2011, 133, 3800–3803; h) E. Anger, M. Ru-
dolph, L. Norel, S. Zrig, C. Shen, N. Vanthuyne, L. Toupet, J. A. G.
Williams, C. Roussel, J. Autschbach, J. Crassous, R. Rꢃau, Chem.
Eur. J. 2011, 17, 14178–14198; i) E. Anger, M. Srebro, N. Vanthuyne,
L. Toupet, S. Rigaut, C. Roussel, J. Autschbach, J. Crassous, R.
Rꢃau, J. Am. Chem. Soc. 2012, 134, 15628–15631; j) C. M. ꢄlvarez,
H. Barbero, L. A. Garcꢅa-Escudero, J. M. Martꢅn-Alvarez, C. Martꢅ-
nez-Pꢃrez, D. Miguel, Inorg. Chem. 2012, 51, 8103–8111; k) O.
Crespo, B. Eguillor, M. A. Esteruelas, I. Fernꢆndez, J. Garcꢅa-
[12] a) C. E. Loader, C. J. Timmons, J. Chem. Soc. C 1968, 330–332;
b) M. J. E. Hewlins, R. Salter, Synthesis 2007, 2164–2174.
[13] E. Licandro, C. Rigamonti, M. T. Ticozzelli, M. Monteforte, C. Bal-
doli, C. Giannini, S. Maiorana, Synthesis 2006, 3670–3678.
[14] a) T. J. Barton, A. J. Nelson, Tetrahedron Lett. 1969, 10, 5037–5040;
b) C. C. Santini, J. Fischer, F. Mathey, A. Mitschler, J. Am. Chem.
9946
www.chemeurj.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 9939 – 9947

Heterohelicenes with Embedded Chiral P Units
FULL PAPER
Soc. 1980, 102, 5809–5815; c) H.-L. Ji, J. H. Nelson, A. DeCian, J.
Fischer, B. Li, C. Wang, B. McCarty, Y. Aoki, J. W. Kenney III, L.
Solujic, E. B. Milosavljevic, J. Organomet. Chem. 1997, 529, 395–
408.
B. Ben Hassine, J. P. Genet, M. Gorsane, J. Madec, L. Ricard, A.
´
Marinetti, Synthesis 2004, 2513–2516; g) I. Stary, I. G. Starꢆ, Z.
ˇ
´
ˇ
Alexandrovꢆ, P. Sehnal, F. Teply, D. Saman, L. Rulisek, Pure Appl.
ˇ
Chem. 2006, 78, 495–499; h) P. Sehnal, I. G. Starꢆ, D. Saman, M.
´
ˇ ˇ ˇ ˇ
Tichy, J. Misek, J. Cvacka, L. Rulisek, J. Chocholousovꢆ, J. Vacek,
[15] a) G. Wittig, A. Maercker, Chem. Ber. 1964, 97, 747–768; b) S.
Gladiali, A. Dore, D. Fabbri, O. De Lucchi, G. Valle, J. Org. Chem.
1994, 59, 6363–6371; c) R.-F. Chen, Q.-L. Fan, C. Zheng, W. Huang,
Org. Lett. 2006, 8, 203–205; d) K. Geramita, J. McBee, T. Don Til-
ley, J. Org. Chem. 2009, 74, 820–829; e) H. A. van Kalkeren,
S. H. A. M. Leenders, C. R. A. Hommersom, F. P. J. T. Rutjes, F. L.
van Delft, Chem. Eur. J. 2011, 17, 11290–11295.
ˇ
´
G. Goryl, M. Szymonski, I. Cisarovꢆ, I. Stary, Proc. Natl. Acad. Sci.
ˇ
´
ˇ ˇ
USA 2009, 106, 13169–13174; i) J. Zꢆdny, A. Jancarꢅk, A. Androno-
va, M. Sꢆmal, J. Chocholousovꢆ, J. Vacek, R. Pohl, D. Saman, I. Cꢅs-
ˇ
ˇ
ˇ
ˇ
´
arovꢆ, I. G. Starꢆ, I. Stary, Angew. Chem. Int. Ed. 2012, 51, 5857–
5861; j) M. R. Crittall, N. W. G. Fairhurst, D. R. Carbery, Chem.
Commun. 2012, 48, 11181–11183.
[16] H. W. Krause, A. Kinting, J. Prakt. Chem. 1980, 322, 485–486.
[17] The configuration of the phosphorus atom in the two epimers of
compound 7b was assigned based on the X-ray crystal structure of
helical derivative (SP,P)-9b (Figure 6).
[18] W. H. Laarhoven, T. J. H. M. Cuppen, R. J. F. Nivard, Tetrahedron
1970, 26, 4865–4881.
[19] For representative examples of helicity control in the diastereoselec-
tive synthesis of helicenes, including photochemical syntheses, see
Ref. [2b] and: a) J. Tribout, R. H. Martin, M. Doyle, H. Wynberg,
Tetrahedron Lett. 1972, 13, 2839–2842; b) J. M. Vanest, R. H.
Martin, Rec. Trav. Chim. Pays-Bas 1979, 98, 113; c) K. Tanaka, H.
Osuga, Y. Shogase, H. Suzuki, Tetrahedron Lett. 1995, 36, 915–918;
d) M. C. CarreÇo, R. Hernꢆndez-Sꢆnchez, J. Mahugo, A. Urbano, J.
Org. Chem. 1999, 64, 1387–1390; e) M. C. CarreÇo, M. Gonzꢆlez-
Lꢇpez, A. Urbano, Chem. Commun. 2005, 611–613; f) R. El Abed,
[20] a) M. Widhalm, L. Brecker, K. Mereiter, Tetrahedron: Asymmetry
2006, 17, 1355–1369; b) W. Egan, R. Tang, G. Zon, K. Mislow, J.
Am. Chem. Soc. 1971, 93, 6205–6216.
[21] For discussions on the stereochemistry of the reductions of cyclic
phosphine oxides, see: a) L. D. Quin, K. C. Caster, J. C. Kisalus,
K. A. Mesch, J. Am. Chem. Soc. 1984, 106, 7021–7032; b) E. H.
Krenske, J. Org. Chem. 2012, 77, 3969–3977, and references therein.
[22] a) D. Nakano, M. Yamaguchi, Tetrahedron Lett. 2003, 44, 4969–
4971; b) M. Monteforte, S. Cauteruccio, S. Maiorana, T. Benincori,
A. Forni, L. Raimondi, C. Graiff, A. Tiripicchio, G. R. Stephenson,
E. Licandro, Eur. J. Org. Chem. 2011, 5649–5658.
Received: March 4, 2013
Published online: June 13, 2013
Chem. Eur. J. 2013, 19, 9939 – 9947
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9947