Catalytic asymmetric allenylation: Regulation of the equilibrium between propargyl- and allenylstannanes during the catalytic process

Article abstract of DOI:10.1002/(SICI)1521-3773(19980918)37:17<2392::AID-ANIE2392>3.0.CO;2-D

Achiral substrates 1 and 2 can be regioselectively converted into chiral allenyl alcohols 3 through the title reaction [Eq. (1)] with the synergetic reagent iPrSBEt₂ and a chiral Ti(IV) catalyst. The dramatic regioselectivity originates from the regulation of the equilibrium between propargyl- and allenylstannanes during the catalytic process.

Full text of DOI:10.1002/(SICI)1521-3773(19980918)37:17<2392::AID-ANIE2392>3.0.CO;2-D

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Â
4: a) Aminophosphane 1 (5 g) is dissolved in a mixture of pentane (150 mL)
and diethyl ether (50 mL), and the resulting solution is stirred for 2 d at
ambient temperature. After all volatile components have been removed in
vacuo, the obtained crude product mixture is subjected to chromatography
on silica gel that has been pretreated with chlorotrimethylsilane. Elution
with pentane furnishes 4 (Rf ˆ 0.9) as a colorless solid; yield: 0.2 g (10.5%).
M.p. 808C. b) Alternatively, the zirconium complex 2b (4 g, 6 mmol) is
dissolved in diethyl ether (150 mL) and treated at ambient temperature
under stirring with triethylammonium chloride (0.83 g, 6 mmol). After the
mixture has been stirred for 4 h, all volatile components are removed in
vacuo, and the remaining solid residue is extracted with pentane. The
combined extracts are evaporated to dryness, and 4 is obtained after
chromatographic workup as described above; yield: 0.29 g (23%). 31P{1H}
NMR (121.5 MHz, CDCl3): d ˆ 4.7 (t, 2J(P,P) ˆ 17.6 Hz, PX), 0.5 (d,
2J(P,P) ˆ 17.6 Hz, PK); 1H{31P} NMR (300 MHz, CDCl3): d ˆ 7.23 (d,
4J(H,H) ˆ 2.7 Hz, 2H, HA), 7.05 (t, 4J(H,H) ˆ 2.7 Hz, 1H, HN); 1H NMR
(500 and 300 MHz, CDCl3): d ˆ 7.23 (m, 2H, HA), 7.05 (m, 1H, HN),
(iteration with WINDAISY gave the following coupling constants (the
signs given are based on a positive sign for 1J(P,H)): 1J(PK,HA) ˆ ‡580.0,
3J(PX,HA) ˆ ‡6.4, 3J(PK,HA) ˆ ‡8.8, 4J(HA,HA) ˆ 5.2, 4J(HA,HN) ˆ
[7] a) J.-P. Majoral, M. Zablocka, A. Igau, N. Cenac, Chem. Ber. 1996, 129,
879 ± 886; b) N. Dufour, J.-P. Majoral, A.-M. Caminade, R. Choukron,
Y. Dromzee, Organometallics 1991, 10, 45 ± 48.
[8] S. S. Krishnamurthy, M. Woods, Annual Reports on NMR Spectro-
scopy 1987, 19, 175 ± 320.
[9] Crystal structrue analysis of 2b: C34H55ClN3PZr, colorless crystals,
Â
Å
0.10  0.20  0.25 mm; Mr ˆ 663.5; triclinic, space group P1 (no. 2),
a ˆ 1042.4(2), b ˆ 1144.8(3), c ˆ 1648.5(2) pm, a ˆ 105.70(2), b ˆ
94.77(2), g ˆ 114.77(2)8, Vˆ 1.6756(6) nm3, Z ˆ 2, m(CuKa) ˆ
4.06 mm 1, Tˆ 200(2) K, F(000) ˆ 704. Of 5371 reflections (2qmax.
ˆ
1208) measured on an Enraf-Nonius CAD4 diffractometer with CuKa
radiation, 4973 were independent and used for all calculations. The
structure was solved with direct methods and refined anisotropically
on F2. Hydrogen atoms were refined with a riding model (program:
SHELXL-93, 364 parameters, 1 restraint); wR2(F2) ˆ 0.101, R(F) ˆ
0.037. An empirical absorption correction (DIFABS, N. Walker,
D.Stuart, Acta Crystallogr. 1983, A39, 158 ± 166) was applied. Crys-
tallographic data (excluding structure factors) for the structure
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no.
CCDC-100765. Copies of the data can be obtained free of charge
on application to CCDC, 12 Union Road, Cambridge CB21EZ, UK
(fax: (‡44)1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
[10] K. Dehnicke, J. Strähle, Polyhedron 1989, 8(6), 707.
‡2.8,
(2J(PK,PK) ˆ ‡10.6,
2J(PK,PX) ˆ ‡16.9,
1J(PX,HN) ˆ ‡589.4,
3
3J(PK,HN) ˆ ‡7.8), 3.1 (m, j J(P,H) ‡ 5J(P,H) jˆ 6, 3J(H,H) ˆ 11.7, 3.6 Hz,
NCH, 4H), 3.0 (dtt, 3J(P,H) ˆ 8, 3J(H,H) ˆ 11.7, 3.5 Hz, NCH, 2H), 1.9 ± 0.9
(m, CH2, 60H); 13C{1H} NMR (75.5 MHz, CDCl3): d ˆ 54.9 (d, 2J(P,C) ˆ
2
5.4 Hz, NC), 54.2 (pseudo t, j J(P,C) ‡ 4J(P,C) jˆ 5.4 Hz, NC), 34.4 (pseudo
[11] G. Erker, W. Frömberg, J. L. Atwood, W. Huttner, Angew. Chem.
1984, 96, 72 ± 73; Angew. Chem. Int. Ed. Engl. 1984, 23, 68.
[12] P. J. Walsh, F. J. Hollander, R. G. Bergman, J. Am. Chem. Soc. 1988,
110, 8729 ± 8731.
[13] A. F. Wells, Structural Inorganic Chemisty, 5. ed., Clarendon, Oxford,
1984.
3
t, j J(P,C) ‡ 5J(P,C) jˆ 1.5 Hz, NCCH2), 34.3 (d, 3J(P,C) ˆ 3.2 Hz, NCCH2),
3
34.1 (pseudo t, j J(P,C) ‡ 5J(P,C) jˆ 1.5 Hz, NCCH2), 27.25, 27.20, 27.15 (s,
NCCCH2), 26.3, 26.2 (s, NCCCCH2); MS (EI, 70 eV): m/z (%): 678 (1)
‡
‡
‡
[M ], 595 (2) [M
c-Hex], 498 (7) [M
N(c-Hex)2], 180 (100) [N(c-
‡
Hex)2 ]; HR-MS (EI, 70 eV): calcd for C36H69N6P3: 678.4797, found:
678.4797.
Received: April 7, 1997 [Z11695IE]
German version: Angew. Chem. 1998, 110, 2486 ± 2488
Keywords: phosphazenes ´ phosphorus heterocycles ´ zirco-
nium
Catalytic Asymmetric Allenylation:
Regulation of the Equilibrium between
Propargyl- and Allenylstannanes during the
Catalytic Process**
[1] a) H. R. Allcock, Phosphorus ± Nitrogen Compounds, Academic
Press, New York, 1972; b) S. S. Krishnamurthy, A. C. Sau, Adv. Inorg.
Chem. Radiochem. 1978, 21, 41; c) R. A. Shaw, Phosphorus and Sulfur
1978, 4, 101; d) ªInorganic and Organometallic Polymersº: ACS Symp.
Ser. 360, ACS, Washington, 1988; e) R. H. Neilson, P. Wisian-Neilson,
Chem. Rev. 1988, 88, 541 ± 562; f) J. E. Mark, H. R. Allcock, R. West,
Inorganic Polymers, Prentice-Hall, Englewood Cliffs, 1992;
g) ªInorganic and Organometallic Polymers IIº: ACS Symp. Ser.
572, ACS, Washigton, 1994; h) I. Manners, Angew. Chem. 1996, 108,
1712 ± 1731; Angew. Chem. Int. Ed. Engl. 1996, 35, 1602 ± 1635.
[2] a) A. Schmidpeter, J. Ebeling, Angew. Chem. 1968, 80, 197; Angew.
Chem. Int. Ed. Engl. 1968, 7, 197; b) A. Schmidpeter, J. Ebeling, H.
Stary, C. Weingand, Z. Anorg. Allg. Chem. 1972, 394, 171 ± 186;
c) H. R. Allcock, P. J. Harris, J. Am. Chem. Soc. 1978, 101, 21, 6221 ±
6228; d) H. R. Allcock, M. S. Connolly, P. J. Harris, J. Am. Chem. Soc.
1982, 104, 2483 ± 2490; e) H. R. Allcock, M. S. Connolly, R. R. Whittle,
Organometallics 1983, 2, 1514 ± 1523; f) H. R. Allcock, J. L. Descorcie,
G. H. Riding, Polyhedron 1987, 6, 119 ± 157.
Chan-Mo Yu,* Sook-Kyung Yoon, Kwangwoo Baek,
and Jae-Young Lee
Dedicated to Professor Elias J. Corey
on the occasion of his 70th birthday
The availability of efficient synthetic methods for achieving
absolute stereoselectivity by catalytic processes in the pro-
duction of enantiomerically pure compounds is of consider-
able current interest because such products can be used as
chiral building blocks for the synthesis of valuable chiral
substances.[1] In this regard, allyl-transfer reactions provide
excellent stereoselective routes for converting aldehydes into
the corresponding alcohols.[2] Subsequent to early studies by
Hoffmann et al.[3] on the use of chirally modified allyl boranes
to accomplish asymmetric induction, many research groups
have made important contributions to the extension of this
[3] A. Schmidpeter, H. Rossknecht, Chem. Ber. 1974, 107, 3146 ± 3148.
[4] E. Niecke, M. Raab, G. Schick, D. Gudat, K. Müllen, unpublished
results.
[5] G. Schick, A. Loew, M. Nieger, E. Niecke, K. Airola, Chem. Ber. 1996,
129, 211 ± 217.
[*] Prof. Dr. C.-M. Yu, S.-K. Yoon, K. Baek, J.-Y. Lee
Department of Chemistry and Institute of Basic Science
Sungkyunkwan University, Suwon 440 ± 746 (Korea)
Fax : (‡ 82)331-290-7075
[6] Chromatographic workup furnished a further fraction consisting of 4
and another cyclophosphazene which gives rise to singlets in both the
31P{1H} and 1H{31P} spectra (d(1H) ˆ 7.36, d(31P) ˆ 0.6). Since the mass
spectrum of this mixture proved to be identical with that of pure 4, and
a simulation of the signal attributable to the PH moiety in the 1H
NMR spectrum as a [AX]3 spectrum was in satisfactory agreement
with the experimental data, we assume the presence of a mixture of 4
and an isomeric cis,cis,cis-tris(hydrido)cyclotriphosphazene.
E-mail: cmyu@chem.skku.ac.kr
[**] This research was supported by grants from the Ministry of Education
(BSRI 97-3420) and the Korea Science and Engineering Foundation
(KOSEF 97-0501-02-01-3).
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protocol to achieve high levels of stereoselectivity.[4] The
exceptional power of the allyl transfer reactions in forming
enantioenriched alcohols from aldehydes has been enhanced
by newly developed catalytic variations, especially the chiral
Lewis acid catalyzed addition of allyl-transfer reagents to
carbonyl functionalities.[5] Although there have been several
elegant reports regarding the enhancement of the catalytic
ability for practical use,[6] the scope of the catalytic allyl-
transfer reactions is still limited to allyl systems.
Recently, we demonstrated that the utilization of molecular
synergetic reagents, designed on the basis of mechanistic
speculation, for catalytic asymmetric allylation and propargy-
lation resulted in not only a significant increase in the reaction
rate but also a reduced dosage of the chiral catalyst.[7] This
strategy should prove to be effective for the catalytic
allenylation of achiral aldehydesÐan efficient method should
enable the many useful functional group transformations of
allenyl alcohols to be realized.[8]
Practical methods for the synthesis of allenyl alcohols are
often limited by the tendency of propargylic reagents to
couple with carbonyl groups to produce allenyl alcohols,
which is mainly a consequence of their lack of regiochemical
selectivity.[9] An efficient method for the enantioselective
synthesis of allenyl alcohols through the self-immolative
transfer of chirality by the use of stoichiometric amounts of
nonracemic propargylstannanes with aldehydes has been
reported.[10] While the reaction of some propargylboranes
with stoichiometric chiral auxiliaries has been developed to
achieve a highly enantio- and regioselective synthesis of
allenyl alcohols,[11] a catalytic version of the allenylation of
aldehydes has not yet been realized. Described herein is an
extension of the molecular accelerating strategy aimed at
finding new reagents and realizing useful and practical ways to
advance to new levels of asymmetric synthesis. In the present
research, two major observations have been made in the
enantioselective synthesis of allenyl alcohols: 1) bifunctional
synergetic reagents expedite the catalytic process of asym-
metric allenylation of achiral aldehydes in high enantioselec-
tivity, and 2) the reaction procedes with dramatic regiochem-
ical selectivities as a result of the equilibrium between the tin
reagents.
The starting point of this investigation was the availability
of the tin reagent 2 in a regiochemically pure form. This
compound was prepared by the following reaction in large
quantites and purified by distillation: The treatment of 1-
bromo-2-butyne (1.2 equiv) with magnesium (2.0 equiv) and
Bu3SnCl (1 equiv) in the presence of PbBr2 (5 mol%) in THF
afforded 2-butynyltributylstannane (2, R2 ˆ Me) in 81% yield
after purification by distillation with a regioselectivity of over
98%.[12] The first study focused on the feasibility of 2 for the
catalytic asymmetric allenylation of achiral aldehydes that
were promoted by a chiral Lewis acid catalyst. Our initial
studies were carried out with 1 (R1 ˆ PhCH2CH2) and 2 (R2 ˆ
Me) in the presence of a (S)-BINOL ± TiIV complex together
with various bifunctional synergetic reagents RnMSR1 (M ˆ B,
Al, Si) [Eq. (1); BINOL ˆ 2,2'-dihydroxy-1,1'-binaphthyl].
Several key findings emerged from the study: 1) the control
experiment revealed that the reaction proceeded only mar-
ginally in the absence of a synergetic reagent (10 mol% of
catalyst, 20oC, 20 h, <10% yield); 2) iPrSBEt2 exhibited
quite high efficiency for the catalytic process; 3) a 2:1 mixture
of the BINOL ± Ti(OiPr)4 complex in the presence of 4-Š
molecular sieves provided the most efficient catalyst;[13] and
4) the best chemical yields and enantioselectivities were
obtained at 20oC in CH2Cl2.
Under optimal conditions, the catalytic allenyl-transfer
reaction was conducted by the dropwise addition of iPrSBEt2
(1.2 equiv) in CH2Cl2 at 20oC to a mixture of 1 (R ˆ
CH2CH2Ph, 1 equiv) and 2 (R ˆ Me, 1.2 equiv) in the
presence of the (S)-BINOL ± TiIV complex (10 mol%) in
CH2Cl2. After 9 h at
20oC, the reaction mixture was
quenched by the addition of a saturated aqueous solution of
NaHCO3. Workup and chromatography on silica gel afforded
alcohol 3a in 85% yield and with 93% ee. This discovery
prompted us to carry out more experiments with other
aldehydes and tin reagents (Table 1).
Table 1. Catalytic asymmetric allenylation of achiral aldehydes [Eq. (1)].[a]
Entry
R1
R2
3
yield[%][b]
ee[%][c]
1
2
3
4
5
6
7
8
PhCH2CH2
PhCH2CH2
PhCH2CH2
n-C6H13
n-C6H13
n-C6H13
Me2CHCH2
Me2CHCH2
Me2CHCH2
Ph
Me
Et
Pr
Me
Et
Pr
Me
Et
Pr
Me
Et
Pr
a
b
c
d
e
f
g
h
i
85
77
71
97
82
72
62[d]
49[d]
41[d]
74
93
96
93
92
95
90
81
81
85
90
97
91
9
10
11
12
j
k
l
Ph
Ph
78
73
[a] All reactions were carried out at 20oC; (S)-BINOL:Ti(OiPr)4 ˆ 2:1
(10 mol%); reaction times t ˆ 9 h, unless otherwise stated. [b] Yields refer
to isolated and purified products. [c] Enantiomeric excesses were deter-
mined by preparation of (‡)-MTPA ester derivatives, analysis by 1H NMR
(all entries) and/or 19F NMR spectroscopy (entries 3, 6), and by HPLC
analysis on a chiral stationary phase (Chiracel OD-H, iPrOH/hexane 10/90,
entries 11, 12). [d] t ˆ 11 h.
The absolute configuration of the predominating enan-
tiomer of the adducts was unambiguously established by
comparison of their specific rotations with that of known
alcohols.[11b] The absolute sense of the asymmetric induction
parallels previous observations on catalytic asymmetric allyl-
ations that employed the (S)-BINOL ± TiIV complex.[7] Table 1
shows that the catalytic process is effective for a variety of
aldehydes and tin reagents in terms of chemical yield and
enantioselectivity. However, a reduced dosage of chiral
catalyst (5 mol%) resulted in diminished chemical yields
and longer reaction times (3a, 20oC, 24 h, 41% yield). The
reaction also produced none or only trace amounts of
isomeric propargylic carbinols (<3%) as judged by 1H
(500 MHz) NMR analysis of the crude products.
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We turned our attention next to the application of this
approach with other allenic or propargylic tin reagents to
enlarge the scope of allylic transfer reactions. During our
investigations, we observed the remarkable regulation of the
equilibrium between allenyl- and propargylstannane reagents
under the reaction conditions used. We were surprised to find
that the reaction of 4 a (87:13 mixture) with 1 (R ˆ
PhCH2CH2, 1 equiv) under the same conditions afforded
the alcohol 3 a (R ˆ PhCH2CH2) in 81% yield and with
91% ee.[14] This high regio- and enantioselectivity in the
formation of allenyl alcohol 3 a from allenyltin 4 a at 20oC
mediated by the BINOL ± TiTV complex is virtually identical
to that seen with propargyltin 2 a (Scheme 1). This is not the
common case; allenyltin reagents usually convert aldehydes
necessary link to the product stability (Scheme 3). Thus, the
origin of regiochemical selectivity for these transformations
might be a result of the thermodynamic stability of the tin
Scheme 3. Formation of 3 and 9 from the equilibrium between 2 and 4.
LA* ˆ chiral Lewis acid catalyst.
reagents as well as subtle geometrical preferences for
orientation in the transition states offered by the complex
catalytic system rather than the original concentration of the
reaction.
Experimental Section
Scheme 1. Catalytic asymmetric allenylation of aldehydes; 3a is precipi-
tated in over a 97% purity together with the isomers of propargyl alcohol.
For yields and ee values with 2a, see Table 1. With 4a: R ˆ PhCh2CH2:
81%, 91% ee; R ˆ n-C6H13: 78%, 92% ee.
Typical procedure for the catalytic allenylation (entry 12 of Table 1): A
flame-dried flask containing (S)-BINOL (57.3 mg, 0.2 mmol) and activated
powdered 4-Š molecular sieves (0.7 g) was evacuated and carefully purged
with nitrogen three times, and then charged with dry CH2Cl2 (2 mL)
followed by freshly distilled Ti(OiPr)4 (freshly prepared, 0.5m in CH2Cl2,
0.2 mL, 0.1 mmol). The mixture was stirred at 25oC for 3 h. The red-brown
mixture was cooled to 20oC in a dry ice ± CCl4 bath, and a solution of
benzaldehyde (1, R1 ˆ Ph, 0.11 g, 1.0 mmol) in CH2Cl2 (0.5 mL) was added.
A solution of tributyl-2-hexynylstannane (2, R2 ˆ Pr, 0.45 g, 1.2 mmol) in
CH2Cl2 (1 mL) was added dropwise to this mixture, followed by the
addition of iPrSBEt2 (0.18 g, 1.25 mmol) in CH2Cl2 (1 mL; by gas-tight
syringe with a syringe pump) over 1 h along the wall of the flask while
keeping the temperature below 20oC. After the reaction mixture was
stirred for 8 h at 20oC, aqueous NaHCO3 (5 mL) was added and then
CH2Cl2 (5 mL). The molecular sieves were removed by filtration, and the
aqueous layer was extracted with CH2Cl2 (ca. 20 mL). The combined
organic solution was dried over anhydrous Na2SO4, and the solvents were
then removed under reduced pressure. Purification of the residue by
column chromatography (EtOAc/hexanes 15/85) afforded 3 (R1 ˆ Ph, R2 ˆ
Pr; 0.137 g, 0.73 mmol, 73%) as a colorless liquid: TLC: Rf ˆ 0.33 (hexane/
into propargyl alcohols in a reaction mediated by a Lewis acid
catalyst in the absence of equilibrating reagents such as
BuSnCl3.[15] On the other hand, both allenyltin 5 and
propargyltin 6, under identical conditions, produced the same
propargyl carbinol 7 as a major component (Scheme 2). In
general, allenyl reagents lead mainly to propargylic adducts,
EtOAc 85/15); [a]D20
ˆ
120 (c ˆ 1.75, CHCl3); FT-IR (neat): nÄ ˆ 3389,
1956 cm 1; EI-MS: m/z (%): 188 (M , 30.6), 173 (24.2), 106 (37.8), 79 (100);
1H NMR (500 MHz, CDCl3): d ˆ 0.86 (t, J ˆ 7.5 Hz, 3H), 1.36 ± 1.46 (m,
2H), 1.70 ± 1.86 (m, 2H), 2.24 (d, J ˆ 4.5 Hz, 1H), 4.96 ± 5.04 (m, 2H), 5.09
(ddd, J ˆ 4.5, 2.5, 2.5 Hz, 1H), 7.20 ± 7.50 (m, 5H); 13C NMR (50 MHz,
CDCl3): d ˆ 13.74, 20.70, 30.01. 74.11, 79.57, 108.05, 126.67, 127.70, 128.26,
142.15, 204.21.
‡
Received: March 31, 1998 [Z11670IE]
Scheme 2. Catalytic asymmetric propargylation with 5[7c] and 6.
German version: Angew. Chem. 1998, 110, 2504 ± 2506
Keywords: aldehydes ´ asymmetric catalysis ´ Lewis acids ´
synthetic methods ´ titanium
and propargylic reagents to allenyl adducts by SE2' addition to
the aldehyde. These apparent contradictions could be ex-
plained by products being formed in the reaction that
originated from the equilibrium between allenyl- and prop-
argyltin reagents under the reaction conditions. Since anti-
periplanar attack would lead to the particular product 3 or 9
via transition state A or B, the major reaction pathway could
be dependent on the stability of the transition state under
kinetic control or on orientations and steric factors, without a
[1] General discussions: a) R. Noyori, Asymmetric Catalysis in Organic
Synthesis, Wiley, New York, 1993, pp. 1 ± 364; b) K. Maruoka, H.
Yamamoto in Catalytic Asymmetric Synthesis (Ed.: I. Ojima), VCH,
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[2] Comprehensive discussions: a) Y. Yamamoto, N. Asao, Chem. Rev.
1993, 93, 2207 ± 2293; b) D. Hoppe, W. R. Roush, E. J. Thomas in
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‡
Stereoselective Synthesis, Vol. 3 (Eds.: G. Helmchen, R. W. Hoffmann,
J. Mulzer, E. Schaumann), Thieme, Stuttgart, 1996, pp. 1357 ± 1602.
[3] a) T. Herold, U. Schrott, R. W. Hoffmann, Chem. Ber. 1981, 114, 359 ±
374; b) R. W. Hoffmann, Angew. Chem. 1982, 94, 569 ± 580; Angew.
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[4] Reviews: a) W. R. Roush in Comprehensive Organic Synthesis, Vol. 2
(Ed.: C. H. Heathcock), Pergamon, Oxford, 1991, pp. 1 ± 53; b) M.
Santell, J.-M. Pons, Lewis Acids and Selectivity in Organic Chemistry,
CRC, New York, 1996, pp. 91 ± 184.
Monocyclic (CH)9 ÐA Heilbronner Möbius
Aromatic System Revealed**
Michael Mauksch, Valentin Gogonea, Haijun Jiao,
Paul von Rague Schleyer*
Â
Dedicated to Professor Edgar Heilbronner
In 1964 Heilbronner predicted that singlet [4n]annulenes
would be aromatic systems in twisted conformations where
the p orbitals lie on the surface of a Möbius strip (Figure 1).[1]
[5] a) K. Ishihara, M. Mouri, Q. Gao, T. Maruyama, K. Furuta, H.
Yamamoto, J. Am. Chem. Soc. 1993, 115, 11490 ± 11495; b) J. A.
Marshall, Y. Tang, Synlett 1992, 653 ± 654; c) A. L. Costra, M. G.
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Soc. 1993, 115, 7001 ± 7002; d) G. E. Keck, K. H. Tarbet, L. S. Geraci,
J. Am. Chem. Soc. 1993, 115, 8467 ± 8468; e) S. Aoki, K. Mikami, M.
Terada, T. Nakai, Tetrahedron 1993, 49, 1783 ± 1792; f) J. W. Faller,
D. W. Sams, X. Liu, J. Am. Chem. Soc. 1996, 118, 1217 ± 1218; g) A.
Yanagisawa, H. Nakashima, A. Ishiba, H. Yamamoto, J. Am. Chem.
Soc. 1996, 118, 4723 ± 4724; h) D. R. Gauthier, Jr., E. M. Carreira,
Angew. Chem. 1996, 35, 2521 ± 2523; Angew. Chem. Int. Ed. Engl.
1996, 35, 2363 ± 2365; i) S. Weigand, R. Brückner, Chem. Eur. J. 1996,
2, 1077 ± 1084; j) P. G. Cozzi, P. Orioli, E. Tagliavini, A. Umani-
Ronchi, Tetrahedron Lett. 1997, 38, 145 ± 148.
Figure 1. Schematic representation of the Möbius type overlapping p
‡
[6] a) S. Casolari, P. G. Gozzi, P. Orioli, E. Tagliavini, A. Umani-Ronchi,
Chem. Commun. 1997, 2123 ± 2124; b) K. Mikami, S. Matsukawa,
Nature 1997, 385, 613 ± 615; c) S. Matsukawa, K. Mikami, Tetrahedron:
Asymmetry 1997, 8, 815 ± 818.
orbitals in (CH)9 . The C2 axis lies horizontally; the carbon atom on it
(right) is across from the phase inversion (left).
[7] a) C.-M. Yu, H.-S. Choi, W.-H. Jung, S.-S. Lee, Tetrahedron Lett. 1996,
37, 7095 ± 7098; b) C.-M. Yu, H.-S. Choi, W.-H. Jung, H.-J. Kim, J. Shin,
Chem. Commun. 1997, 761 ± 762; c) C.-M. Yu, S.-K. Yoon, H.-S. Choi,
K. Baek, Chem. Commun. 1997, 763 ± 764; d) C.-M. Yu, H.-S. Choi, S.-
K. Yoon, W.-H. Jung, Synlett 1997, 889 ± 890.
[8] a) J. A. Marshall, M. A. Wolf, E. M. Wallace, J. Org. Chem. 1997, 62,
367 ± 371; b) R. W. Friesen, C. Vanderwal. J. Org. Chem. 1996, 61,
9103 ± 9110, and references therein.
[9] Reviews: a) H. Yamamoto in Comprehensive Organic Synthesis, Vol. 2
(Ed.: C. H. Heathcock), Pergamon, Oxford, 1991, pp. 81 ± 98; b) C.
Bruneau, P. H. Dixneuf in Comprehensive Organic Functional Group
Transformations, Vol. 1 (Eds.: A. R. Katritzky, O. Meth-Cohn, C. W.
Rees), Elsevier, Oxford, 1995, pp. 953 ± 998.
[10] J. A. Marshall, R. H. Yu, J. P. Perkin, J. Org. Chem. 1995, 60, 5550 ±
5555.
[11] a) E. J. Corey, C.-M. Yu, D.-H. Lee, J. Am. Chem. Soc. 1990, 112, 878 ±
879; b) H. C. Brown, S. V. Kulkarni, Tetrahedron Lett. 1996, 37, 4125 ±
4128.
[12] Allenyltin compounds are reported (H. Tanaka, A. K. M. Abdul Hai,
H. Ogawa, S. Torri, Synlett 1993, 835 ± 836) to be obtained under
conditions similar to those we used to obtain propargyltin compounds
from 3-substituted propargyl bromides.
[13] The role of molecular sieves for the TiIV-promoted reaction was
reported; see a) ref. [5c]; b) M. Terada, Y. Matsumoto, Y. Nakamura,
K. Mikami, Chem. Commun. 1997, 281 ± 282.
Although the Möbius concept has been employed extensively
to interpret reactions and bonding,[2,3] Möbius annulenes
conforming to Heilbronnerꢁs original idea have still not been
reported. Heilbronner pointed out that rings with twenty
atoms or more might adopt Möbius geometries ªwithout any
apparent angle or steric repulsion strainº.[1] However, we have
discovered computationally that Möbius aromaticity is possi-
ble in a much smaller ring system, namely, the cyclononate-
traenyl cation. Moreover, judging from early experimental
evidence,[4,5] this species may actually have been encountered
more than once almost three decades ago!
‡
A monocyclic (CH)9 cation of unspecified nature, but
which allowed isotope label scrambling, was first postulated in
1971 as a short-lived intermediate in the solvolysis of exo-9-
chlorobicyclo[6.1.0]nona-2,4,6-triene in aqueous acetone at
758C.[4] The reactant containing deuterium at C9 (1,
Scheme 1) gave a bicyclic product, cis-8,9-dihydroindene-1-
ol (3, X ˆ OH), with uniformly distributed deuterium label.[4]
Shortly afterwards Anastassiou and Yakali succeeded in
preparing 9-chlorocyclononatetraene (2, stereochemistry un-
determined).[6] Under ionizing conditions (liquid SO2 at
668C), D-labeled 2 gave 3 (X ˆ Cl) by ion-pair return,
again with complete statistical distribution of the label (1/9D
per C atom).[5]
[14] The reagent 4 was prepared by the reaction of 2-butynyl pivaloate
with (Bu3Sn)2CuLi at
78oC in THF. Although the literature
procedure can be used to prepare regiochemically pure triphenyltin
analogues of 4 and 6, it turned out to be unpromising for this purpose
mainly because of the lack of reactivity.
[15] J. A. Marshall, Chem. Rev. 1996, 96, 31 ± 47, and references therein.
[*] Prof. Dr. P. von R. Schleyer, Dipl.-Chem. M. Mauksch,
Dr. V. Gogonea, Dr. H. Jiao
Computer-Chemie-Centrum
Institut für Organische Chemie der Universität Erlangen-Nürnberg
Henkestrasse 42, D-91054 Erlangen (Germany)
Fax: ( ‡ 49)9131-85-9132
E-mail: pvrs@organik.uni-erlangen.de
[**] We thank Prof. Emel Yakali (Raymond Walters College, Cincinnati,
OH) for helpful discussions and Holger Bettinger (CCQC, Athens,
GA) for the CCSD(T) computations. We are grateful to the Deutsche
Forschungsgemeinschaft, the Humboldt Foundation (fellowship for
V.G.), and the Fonds der Chemischen Industrie for their financial
support.
Angew. Chem. Int. Ed. 1998, 37, No. 17
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