Cascade pericyclic reactions of alleno-acetylenes: Facile access to highly substituted cyclobutene, dendralene, pentalene, and indene skeletons

Article abstract of DOI:10.1002/chem.201102852

Fine tuning of cascade reaction pathways: The allene core of 1,3-di-tert-butyl-1,3-diethynylallenes has been shown in the past to be essentially unreactive. However, its inherent reactivity could be unleashed by the introduction of tailored substituents to induce a variety of highly selective reaction cascades (e.g. 4π electrocyclization, see scheme). These novel processes provide rapid access to densely functionalized carbon skeletons of high molecular complexity in one-pot operations. Copyright

Full text of DOI:10.1002/chem.201102852

DOI: 10.1002/chem.201102852
Cascade Pericyclic Reactions of Alleno-Acetylenes: Facile Access to Highly
Substituted Cyclobutene, Dendralene, Pentalene, and Indene Skeletons
Corinna M. Reisinger, Pablo Rivera-Fuentes, Samuel Lampart, W. Bernd Schweizer, and
FranÅois Diederich*[a]
Cascade reactions are valuable tools for building complex
molecular architectures with high efficiency, selectivity, and
atom economy. These processes have a proven record in the
preparation of natural products and biologically relevant
molecules.[1] In a similar manner, cascade transformations
would greatly benefit the field of advanced materials sci-
ence, where they offer opportunities for rapid and divergent
synthetic elaboration, thereby expanding the chemical space
for functional materials.
tween the allene core and the proximal dicyanovinyl moiety,
to give cyclobutene 3a (Scheme 1). In a similar way, buta-
diene (Æ)-2b could be transformed into cyclobutene 3b, in
which water was eliminated from the acetonide protecting
group. The molecular structures of cyclobutenes 3a and 3b
were unambiguously assigned by X-ray diffraction studies
(Scheme 1; for details, see the Supporting Information).[10]
The triple CA/CR/EC cascade also produced dicyanocyclo-
butenes 18 and 19 (see Scheme SI1 in the Supporting Infor-
mation) in high yield (82–87%) with the acetonide protect-
ing group replaced by an iPr3Si substituent. We found that
addition of 10 equivalents of trifluoroacetic acid (TFA) ac-
celerates the reaction and increases the yields significantly.
It can be inferred that TFA protonates the aniline nitrogen,
quenching the intramolecular charge-transfer interaction,
and in turn making the dicyanoolefin more electron-defi-
cient, and hence more reactive.[2a] Concomitantly, protona-
tion may also lead to a conformational change that favors
the electrocyclization. The TCNQ- and TCNE-derived di-
cyanocyclobutenes feature interesting opto-electronic prop-
erties that are currently further exploited. Thus, the intense
intramolecular charge-transfer (CT) band of 3a appears at
649 nm (e =30400mÀ1 cmÀ1), whereas the corresponding
band of 3b has lmax =471 nm (e =39300mÀ1 cmÀ1). The CA/
CR steps display identical chemo- and regioselectivity as re-
ported before.[9b] Additionally, the 4p EC reaction is stereo-
selective, giving a single isomer (E) of the exocyclic double
bond of the formed cyclobutene. Theoretical calculations
(see the Supporting Information) showed that the energy of
the (Z)-configured product is 5.5 kcalmolÀ1 higher than that
of the (E)-configured isomer, thus revealing that the latter is
thermodynamically favored.
In an attempt to prepare DEA (Æ)-5a, bearing a 1,1-di-
methylhomoallyl appendage, by Pd-catalyzed SN2’-reaction
of bispropargylic ester (Æ)-4 (for preparation, see the Sup-
porting Information) with acetylenic nucleophiles,[4] another
cascade transformation was discovered (Scheme 2A). Signif-
icant amounts of a by-product were detected from the very
first runs, which after isolation and characterization was
identified as the buta-1,3-diene 6a. Heating pure (Æ)-5a in
1,2-dichloroethane induced the clean formation of buta-1,3-
diene 6a in high yield and as a single double-bond (E)
isomer (NOE correlations). This experiment demonstrates
that compound 6a arises from the in situ thermal rearrange-
ment of allene (Æ)-5a. The transformation of allene (Æ)-5a
Allenes are particularly interesting candidates for the de-
velopment of cascade reactions, given the diversity and spe-
cificity of their reaction modes.[2] Our interest in alleno-ace-
tylenic scaffolding prompted us to introduce allenes as
building blocks in the construction of three-dimensional
chiral carbon-rich structures. To be able to prepare stable
alleno-acetylenic chromophores, the 1,3-di-tert-butyl-1,3-di-
ethynylallene (DEA) moiety was developed.[3] The introduc-
tion of tert-butyl substituents provides steric hindrance to
the allene core, reducing its reactivity considerably. Taking
advantage of the kinetic stability of these alleno-acetylenic
scaffolds, we were able to resolve their enantiomers,[4] and
use them to build enantiopure chiral push–pull chromo-
phores,[4,5] macrocycles,[6] and helical foldamers.[7] Here, we
explore the potential of the allene core of DEAs to partici-
pate in cascade pericyclic reactions, which lead to highly
substituted complex carbon skeletons in a one-pot fashion,
with excellent chemo-, regio-, and stereoselectivities.[8]
We first investigated the reaction between racemic DEA
(Æ)-1 and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) and
1,1,2,2-tetracyanoethene (TCNE), to give butadienes (Æ)-2a
and (Æ)-2b, respectively, by a formal [2+2] cycloaddition,
followed by cycloreversion (CA/CR).[9] While the reaction
with TCNE proceeded cleanly at room temperature,[4] we
noticed that when the reaction with TCNQ was carried out
at 408C, a significant amount of a by-product was formed.
Isolation and characterization of this compound showed that
adduct (Æ)-2a undergoes a 4p electrocyclization (EC) be-
[a] Dr. C. M. Reisinger, P. Rivera-Fuentes, S. Lampart,
Dr. W. B. Schweizer, Prof. F. Diederich
Laboratorium fꢀr Organische Chemie, ETH Zꢀrich
Hçnggerberg, HCI, CH-8093 Zurich (Switzerland)
Fax : (+41)44-632-1109
E-mail: diederich@org.chem.ethz.ch
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201102852.
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COMMUNICATION
Scheme 1. CA/CR/4p EC cascade reaction: Formation of butadienes (Æ)-2 and cyclobutenes 3, and X-ray crystal structures of 3a and 3b. Hydrogen
atoms and minor occupied positions of disordered atoms (3b) omitted for clarity; atomic displacement parameters obtained at 100 K are drawn at 50%
probability level (for details see the Supporting Information).[10] Reaction conditions: a) TCNQ (1 equiv), CH2Cl2, 258C, 4 h, 98%; b) TFA (10 equiv),
(CH2Cl)2, 608C, 1 h, 55%; c) TCNE (1 equiv), CH2Cl2, 258C, 1 h, 91%; d) TFA (10 equiv), (CH2Cl)2, 608C, 4 h, 60%.
to buta-1,3-diene (E)-6a amounts to an allenyl-Cope [3,3]-
sigmatropic rearrangement. Intrigued by the remarkable
ease of the allenyl-Cope rearrangement of DEA (Æ)-5a,
compared to prior known examples,[11] we eagerly probed
modified substrates (Æ)-5b–f bearing different para-substi-
tuted phenyl rings (Scheme 2B) and their propensity to give
buta-1,3-dienes 6b–f. The allenyl-Cope rearrangement was
found to be substantially accelerated in the case of electron-
withdrawing substituents (p-CN and in particular p-NO2, see
Table in Scheme 2), and conversions after a reaction time of
1 h were considerably higher than those of the parent
phenyl-substituted derivative (6b (p-H): 40%; 6 f (p-NO2):
67%). This allenyl-Cope rearrangement of DEAs allows
facile access to highly substituted, sterically congested buta-
1,3-diene systems in a stereoselective manner.[12] Theoretical
calculations predict rotational barriers about their central
C–C single bond in the range of 20 kcalmolÀ1 (see the Sup-
porting Information). With the aid of the calculations, we
further rationalized that the observed (E)-stereoselectivity
most likely results from steric control by the tert-butyl sub-
stituent in the transition state of the [3,3]-sigmatropic rear-
rangement (cf. Scheme 2A; for details, see the Supporting
Information). The observation that electron-withdrawing
substituents considerably facilitate the allenyl-Cope rear-
rangement led us to introduce the more potent electron-ac-
cepting 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) moiety by
the CA/CR reaction. Exposure of N,N-dimethylanilino
(DMA)-substituted DEA (Æ)-5c to TCNE led to the forma-
tion of the TCBD derivative (Æ)-7, which was readily con-
verted to the rearranged product, [4]dendralene 8, within
one hour upon heating to reflux in 1,2-dichloroethane. Re-
markably, cyclobutene formation via competing 4p EC (cf.
Scheme 1) of the TCBD-substituted allene intermediate
(Æ)-7 could not be detected over the course of the reaction,
underlining its excellent selectivity. Gratifyingly, the CA/
CR/allenyl-Cope reaction one-pot cascade also took place
smoothly at room temperature over a period of 40 h. Moni-
toring the reaction by NMR spectroscopy revealed the very
rapid formation of the TCBD-substituted allene (Æ)-7 and
its subsequent, slower skeletal reorganization by the [3,3]-al-
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F. Diederich et al.
ture of rapidly interconverting
conformers at room tempera-
ture in contrast to [4]dendra-
lene 8. The release of steric
constraints by the introduction
of an alkyne spacer in diyne
substrate (Æ)-9 also allowed the
use of the more sterically de-
manding TCNQ instead of
TCNE, with the cascade se-
quence still operating under
mild reaction conditions (for
details, see the Supporting In-
formation). Intriguingly and de-
pending on the precise reaction
conditions, the cascade reaction
depicted in Scheme 3A does
not necessarily stop with the
formation of [4]dendralene 8.
Indeed, heating product 8 to
1008C over 12 h causes a fur-
ther highly selective rearrange-
ment sequence which ultimately
furnishes 1,2,4,5-tetrahydropen-
talene (Æ)-12 in nearly quanti-
tative amounts (94% yield;
Scheme 3C). The sequence of
events may be regarded as a
Nazarov-type cyclization fol-
lowed by ring closure of the re-
sulting intermediate (for details,
see the Supporting Informa-
Scheme 2. A) First attempts towards the synthesis of 1,1-dimethylhomoallyl-substituted allene (Æ)-5a and its
thermal rearrangement. Reaction conditions: a) 2-methylbut-3-yn-2-ol (2-5 equiv), [PdCl2A(PPh3)2] or [Pd-
(PPh3)4] (10 mol%), CuI (10 mol%), various amine bases (iPrNH2, iPr2NH, iPr2NEt, among others; 2–
5 equiv), solvent ((CH2Cl)2 or toluene (0.02–0.2m)), 25–608C, 24–72 h; varying yields of allene and buta-1,3-
diene products were isolated; b) (CH2Cl)2 (0.02m), reflux, 10 h; 6a: 86%. B) Thermal allenyl-Cope rearrange-
ment of aryl-substituted allenes (Æ)-5b–f. Reaction conditions: a) (CH2Cl)2 (0.02m), reflux, 1 h; yields of buta-
1,3-diene products 6b–f were determined by 1H NMR spectroscopy with triphenylmethane as internal stan-
dard; b) average of two runs.
CTHUNGTRENNUNG
ACHTUNGTRENNUNG
lenyl-Cope pathway (for details, see the Supporting Infor-
mation). The molecular structure of [4]dendralene 8 was es-
tablished by X-ray crystallography (Scheme 3A and the
Supporting Information).[10] NMR spectroscopy revealed the
co-existence of different conformers at room temperature,
which converged to a single species upon heating to 1008C.
In accordance to previous studies,[13] slow interconversion of
similar dendralenes at room temperature is a consequence
of steric crowding.
These steric constraints may already be present in the
transient intermediate (Æ)-7 and impede favorable orbital
overlap in the transition state of the allenyl-Cope rearrange-
ment. Thus, we reasoned that alleviating the steric con-
straints should lead to an even more facile rearrangement
cascade. Indeed, diyne substrate (Æ)-9 reacted with TCNE
at room temperature to form intermediate (Æ)-10, which
subsequently produces buta-1,3-diene 11 in a significantly
shorter reaction time (Scheme 3B, formation of 8 at 288C:
40 h; of 11: 2.5 h). NMR studies revealed a very rapid Cope
rearrangement event rather than accumulation of the
TCBD-substituted allene intermediate (Æ)-10 in the reac-
tion mixture, as opposed to what was observed in the reac-
tion of alleno-acetylene (Æ)-5c (see the Supporting Informa-
tion).[14] Rearranged product 11 displays a single set of sig-
nals in NMR spectroscopy, suggesting that it exists as a mix-
tion). The molecular structure of compound (Æ)-12 was con-
firmed by X-ray crystallography (Scheme 3C and the Sup-
porting Information).[10] It is a homo-conjugated CT chro-
mophore, and its UV/Vis spectrum reveals the bathochromi-
cally shifted but low-intensity intramolecular CT band char-
acteristic for homo-conjugated push–pull chromophores (see
the Supporting Information).[15]
The manner in which the rate of the allenyl-Cope rear-
rangement can be manipulated by judicious introduction of
electronic- and steric-biasing elements (cf. Scheme 3) mani-
fests itself dramatically in the transformations of isomeric
allene (Æ)-13, in which the 1,1-dimethylhomoallyl lateral
chain has exchanged positions with the tert-butyl substituent
(Scheme 4A). The fact that the [3,3]-allenyl Cope rear-
rangement of compound (Æ)-13 remains extremely slow at
room temperature (<5% after 48 h) opens up an entirely
new reaction pathway for DEA (Æ)-13. Exposure to TCNE
at room temperature now generates intermediate (Æ)-14,
which reacts further to produce the 2,6,7,7a-tetrahydro-1H-
indene skeleton (Æ)-15 in very high yield and short reaction
time (Scheme 4A). Presumably, an intramolecular Diels–
Alder reaction of diene-allene (Æ)-14 accounts for the ob-
served result, thereby shutting down both the [3,3]-sigma-
tropic (and subsequent Nazarov-type cyclization) and the 4p
electrocyclization pathways in favor of a [4+2] reaction
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Cascade Pericyclic Reactions of Alleno-Acetylenes
COMMUNICATION
Scheme 3. CA/CR/allenyl-Cope cascade reaction: A) Formation of [4]dendralene 8 from (Æ)-5c and X-ray crystal structure of 8. Hydrogen atoms and
minor occupied positions of disordered atoms are omitted for clarity; atomic displacement parameters obtained at 100 K are drawn at 50% probability
level (for details see the Supporting Information).[10] Reaction conditions: a) TCNE (1.05 equiv), (CH2Cl)2 (0.02m), 908C, 1 h, 90%; b) TCNE
(1.05 equiv), CH2Cl2 (0.02m), 288C, 40 h, 96%. B) Formation of buta-1,3-diene 11 from diyne (Æ)-9. Reaction conditions: a) TCNE (1.05 equiv), CH2Cl2
(0.02m), 288C, 2.5 h, 93%. C) Thermal rearrangement of 8 to (Æ)-12 and X-ray crystal structure of (Æ)-12. Hydrogen atoms are omitted for clarity;
atomic displacement parameters obtained at 100 K are drawn at 50% probability level (for details see the Supporting Information).[10] Reaction condi-
tions: a) (CDCl2)2 (0.028m), 1008C, 12 h, 94%.
mode.[16] X-ray diffraction studies (Scheme 4A and the Sup-
porting Information) allowed the unambiguous structural as-
signment of tetrahydroindene (Æ)-15,[10] which was obtained
as a mixture of diastereoisomers ((Æ)-15a and (Æ)-15b). Pu-
tatively, the co-existence of the two diastereoisomeric forms
(Æ)-15a and (Æ)-15b at room temperature is a result of hin-
dered rotation about the butadiene axis (cf. Scheme 4A).
However, the convergence of the diastereoisomeric mixture
to a single product (Æ)-15a was accomplished by heating
(Æ)-15b at 1208C for 5.5 h, thus suggesting that tetrahy-
droindene (Æ)-15a is thermodynamically favored over its
isomer (Æ)-15b. Whilst the diastereoselectivity of the Diels–
Alder reaction triggered by the addition of TCNE to allene
(Æ)-13 is high (91:9), the corresponding stereoisomeric tetra-
hydroindenes stemming from the reaction of alleno-acety-
lene (Æ)-13 with TCNQ are formed in almost equimolar
amounts (Scheme 4B). It is particularly remarkable that
even heating the individual pairs of diastereoisomers (Æ)-
16a and (Æ)-16b to 1208C over extended time periods did
not cause any interconversion.
In conclusion, we have developed multiple cascade trans-
formations of 1,3-diethynylallenes, which constitute kineti-
cally stable and easy to handle “reactivity reservoirs”. The
cascades are triggered by the reaction of TCNE or TCNQ
with donor-substituted alkynes by a [2+2] cycloaddition/cy-
cloreversion (CA/CR) sequence and terminated by a) 4p
electrocyclization, b) allenyl-Cope (followed by a Nazarov-
type-cyclization/cyclization sequence), or c) [4+2] cycload-
dition reaction. These novel cascade reactions provide rapid
access, in one-pot processes, to highly substituted cyclobu-
tenes, dendralenes, tetrahydropentalenes, and tetrahydroin-
denes, chromophoric advanced materials with great molecu-
lar complexity. Most remarkably, the reaction pathway can
be steered at will by the judicious introduction of tailored
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F. Diederich et al.
Scheme 4. CA/CR/Diels–Alder reaction cascade: A) Formation of diastereoisomeric tetrahydroindenes (Æ)-15a and (Æ)-15b from DMA-substituted
alleno-acetylene (Æ)-13 and X-ray crystal structures of (Æ)-15a and (Æ)-15b. Hydrogen atoms and minor occupied positions of disordered atoms ((Æ)-
15b) are omitted for clarity; atomic displacement parameters obtained at 100 K are drawn at 50% probability level (for details see the Supporting Infor-
mation).[10] Reaction conditions: a) TCNE (1.05 equiv), CH2Cl2 (0.02m), 30 min, (Æ)-15a: 89% and (Æ)-15b: 9%. B) Formation of diastereoisomeric tet-
rahydroindenes (Æ)-16a and (Æ)-16b from (Æ)-13. Reaction conditions: a) TCNQ (1.05 equiv), CH2Cl2 (0.02m), 72 h, (Æ)-16a: 50% and (Æ)-16b: 38%.
substituents to the alleno-acetylenic core. Current efforts
are aimed at expanding the scope and complexity of these
cascade processes and exploring enantioselective variants
when working with optically pure starting materials.
[1] a) L. F. Tietze, G. Brasche, K. Gericke Domino Reactions in Organic
Synthesis, Wiley-VCH, Weinheim, 2006; b) K. C. Nicolaou, J. S.
Chen, Chem. Soc., Rev. 2009, 38, 2993–3009; c) I. Vilotijevic, T. F.
Jamison, Angew. Chem. 2009, 121, 5352–5385; Angew. Chem. Int.
Ed. 2009, 48, 5250–5281; d) C. Grondal, M. Jeanty, D. Enders, Nat.
Chem. 2010, 2, 167–178; e) E. A. Anderson, Org. Biomol. Chem.
2011, 9, 3997–4006.
[2] a) Modern Allene Chemistry, Vol. 2 (Eds.: N. Krause, A. S. K.
Hashmi), Wiley-VCH, Weinheim, 2008; for recent reviews on cross-
coupling and cycloaddition reactions, see: b) B. Alcaide, P. Almen-
dros, R. Carrascosa, T. Martꢂnez del Campo, Chem. Eur. J. 2010, 16,
5836–5842; c) F. Lꢃpez, J. L. MascareÇas, Chem. Eur. J. 2011, 17,
418–428.
Acknowledgements
[3] a) R. C. Livingston, L. R. Cox, V. Gramlich, F. Diederich, Angew.
Chem. 2001, 113, 2396–2399; Angew. Chem. Int. Ed. 2001, 40, 2334–
2337; b) R. Livingston, L. R. Cox, S. Odermatt, F. Diederich, Helv.
Chim. Acta 2002, 85, 3052–3077; c) S. Odermatt, J. L. Alonso-
Gꢃmez, P. Seiler, M. M. Cid, F. Diederich, Angew. Chem. 2005, 117,
5203–5207; Angew. Chem. Int. Ed. 2005, 44, 5074–5078. For repre-
sentative examples of allenic structures of other research groups,
see: d) S. Thorand, F. Vçgtle, N. Krause, Angew. Chem. 1999, 111,
3929–3931; Angew. Chem. Int. Ed. 1999, 38, 3721–3723; e) M. D.
C.M.R. acknowledges the Alexander von Humboldt Foundation for a
Feodor-Lynen postdoctoral fellowship and P. R.-F. the Stipendienfonds
der Schweizerischen Chemischen Industrie (SSCI) for a doctoral fellow-
ship. This research was supported by the European Research Council
(ERC Advanced Grant No. 246637 “OPTELOMAC”).
Keywords: allenes
· cascade reactions · cyclobutenes ·
dendralenes · indenes · pentalenes
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Cascade Pericyclic Reactions of Alleno-Acetylenes
COMMUNICATION
Clay, A. G. Fallis, Angew. Chem. 2005, 117, 4107–4110; Angew.
Chem. Int. Ed. 2005, 44, 4039–4042; f) M. Leclꢄre, A. G. Fallis,
Angew. Chem. 2008, 120, 578–582; Angew. Chem. Int. Ed. 2008, 47,
568–572.
Duncan, R. T. Hendricks, K. S. Kwong, J. Am. Chem. Soc. 1990, 112,
8433–8442; d) E. Vedejs, A. Cammers-Goodwin, J. Org. Chem.
1994, 59, 7541–7543; for theoretical studies, see: e) J. A. Duncan,
J. K. Azar, J. C. Beathe, S. R. Kennedy, C. M. Wulf, J. Am. Chem.
Soc. 1999, 121, 12029–12034; f) J. A. Duncan, M. C. Spong, J. Org.
Chem. 2000, 65, 5720–5727; related sigmatropic processes are re-
viewed in g) J. J. Gajewski Hydrocarbon Thermal Isomerizations,
2nd ed., Elsevier, Amsterdam, 2004, pp. 171–209.
[4] J. L. Alonso-Gꢃmez, P. Schanen, P. Rivera-Fuentes, P. Seiler, F. Die-
derich, Chem. Eur. J. 2008, 14, 10564–10568.
[5] J. L. Alonso-Gꢃmez, A. G. Petrovic, N. Harada, P. Rivera-Fuentes,
N. Berova, F. Diederich, Chem. Eur. J. 2009, 15, 8396–8400.
[6] a) J. L. Alonso-Gꢃmez, P. Rivera-Fuentes, N. Harada, N. Berova, F.
Diederich, Angew. Chem. 2009, 121, 5653–5656; Angew. Chem. Int.
Ed. 2009, 48, 5545–5548; b) P. Rivera-Fuentes, J. L. Alonso-Gꢃmez,
A. G. Petrovic, P. Seiler, F. Santoro, N. Harada, N. Berova, H. S.
Rzepa, F. Diederich, Chem. Eur. J. 2010, 16, 9796–9807; c) P.
Rivera-Fuentes, B. Nieto-Ortega, W. B. Schweizer, J. T. Lꢃpez Nav-
arrete, J. Casado, F. Diederich, Chem. Eur. J. 2011, 17, 3876–3885.
[7] P. Rivera-Fuentes, J. L. Alonso-Gꢃmez, A. G. Petrovic, F. Santoro,
N. Harada, N. Berova, F. Diederich, Angew. Chem. 2010, 122, 2296–
2300; Angew. Chem. Int. Ed. 2010, 49, 2247–2250.
[12] a) K. W. F. Kohlrausch, H. Wittek, Ber. Dtsch. Chem. Ges. 1942, 75,
227–232; b) G. Kçbrich, A. Mannschreck, R. A. Misra, G. Riss-
mann, M. Rçsner, W. Zꢀndorf, Chem. Ber. 1972, 105, 3794–3806;
c) M. Rçsner, G. Kçbrich, Angew. Chem. 1974, 86, 775–776; Angew.
Chem. Int. Ed. Engl. 1974, 13, 741–742; d) M. Yamada, P. Rivera-
Fuentes, W. B. Schweizer, F. Diederich, Angew. Chem. 2010, 122,
3611–3615; Angew. Chem. Int. Ed. 2010, 49, 3532–3535, and refer-
ences therein; e) M. Betz, H. Hopf, L. Ernst, P. G. Jones, Y. Okamo-
to, Chem. Eur. J. 2011, 17, 231–247.
[13] M. Kivala, C. Boudon, J.-P. Gisselbrecht, P. Seiler, M. Gross, F. Die-
derich, Angew. Chem. 2007, 119, 6473–6477; Angew. Chem. Int. Ed.
2007, 46, 6357–6360.
[8] For an account of allene-multiple bond cycloadditions, see: F. Inaga-
ki, S. Kitagaki, C. Mukai, Synlett 2011, 594–614.
[9] a) T. Michinobu, C. Boudon, J.-P. Gisselbrecht, P. Seiler, B. Frank,
N. N. P. Moonen, M. Gross, F. Diederich, Chem. Eur. J. 2006, 12,
1889–1905; b) M. Kivala, C. Boudon, J.-P. Gisselbrecht, P. Seiler, M.
Gross, F. Diederich, Chem. Commun. 2007, 4731–4733.
[10] CCDC-834582 (3a), CCDC-834583 (3b), CCDC-834584 (8), CCDC-
834587 ((Æ)-12), CCDC-834585 ((Æ)-15a), and CCDC-834586 ((Æ)-
15b) contain 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
[14] Control experiments with blank samples of both monoyne (Æ)-5c
and diyne (Æ)-9 confirmed the accelerating effect of the TCBD unit
on the allenyl-Cope rearrangement.
[15] For a recent study on homoconjugated charge-transfer chromo-
phores, see: S.-I. Kato, M. T. R. Beels, P. La Porta, W. B. Schweizer,
C. Boudon, J.-P. Gisselbrecht, I. Biaggio, F. Diederich, Angew.
Chem. 2010, 122, 6343–6347; Angew. Chem. Int. Ed. 2010, 49, 6207–
6211.
[16] For a related intramolecular Diels–Alder reaction of ene-allenes,
see: R. A. Gibbs, K. Bartels, R. W. K. Lee, W. H. Okamura, J. Am.
Chem. Soc. 1989, 111, 3717–3725.
[11] a) A. Doutheau, G. Balme, M. Malacria, J. Gore, Tetrahedron 1980,
36, 1953–1960; b) J. A. Duncan, D. S. Bohle, C. A. Blanchard, M. L.
Bosse, T. W. Noland, C. M. Ford, M. A. Powell, M. C. Sutton, A. C.
Eggleston, J. Am. Chem. Soc. 1982, 104, 2837–2839; c) J. A.
Received: September 13, 2011
Published online: October 5, 2011
Chem. Eur. J. 2011, 17, 12906 – 12911
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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