Dearomatizing anionic cyclization and novel skeletal rearrangement: High yield formation of multiply substituted bicyclic or polycyclic spirocyclopentadienes and phenanthrene derivatives from 4-aryl 1-lithio-1,3-butadienes

Article abstract of DOI:10.1021/jo070160u

(Chemical Equation Presented) Both 4-phenyl 1-lithio-1,3-butadienes and 4-naphthyl 1-lithio-1,3-butadienes underwent highly efficient and selective intramolecular nucleophilic addition of the butadienyllithium to the aromatic rings, resulting in full dear

Full text of DOI:10.1021/jo070160u

Dearomatizing Anionic Cyclization and Novel Skeletal
Rearrangement: High Yield Formation of Multiply Substituted
Bicyclic or Polycyclic Spirocyclopentadienes and Phenanthrene
Derivatives from 4-Aryl 1-Lithio-1,3-butadienes
Lantao Liu,† Zhihui Wang,‡ Fei Zhao,‡ and Zhenfeng Xi*,‡,§
Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of
Sciences, Beijing 100080, China, Key Laboratory of Bioorganic Chemistry and Molecular Engineering of
Ministry of Education, College of Chemistry, Peking UniVersity, Beijing 100871, China, and State Key
Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of
Sciences, Shanghai 200032, China
zfxi@pku.edu.cn
ReceiVed January 26, 2007
Both 4-phenyl 1-lithio-1,3-butadienes and 4-naphthyl 1-lithio-1,3-butadienes underwent highly efficient
and selective intramolecular nucleophilic addition of the butadienyllithium to the aromatic rings, resulting
in full dearomatization of the phenyl rings and partial dearomatization of the naphthyl rings. When the
reactions were carried out at lower temperatures, ipso intramolecular nucleophilic attack took place
exclusively to afford the spirocyclopentadiene derivatives upon hydrolysis or further treatment with a
variety of electrophiles. 4-Naphthyl 1-lithio-1,3-butadienes and 4-phenyl 1-lithio-1,3-butadienes were
found to proceed in this reaction under similar conditions, with the former being faster even at -78 °C.
However, when the reaction of 4-naphthyl 1-lithio-1,3-butadienes was carried out at higher temperatures,
such as 75 °C, an interesting skeletal rearrangement took place to afford the vicinal attack products,
tetrasubstituted phenanthrenes, via a dearomatization/rearomatization process. Mechanistic investigation
revealed that the kinetically favored ipso attack intermediates might undergo thermal skeletal rearrangement
via 1,2-alkyl shift.
Introduction
organometallic reagents to aromatic compounds8-17 are among
the most frequently used methods for dearomatizing the stable
Activation and application of unreactive molecular structures
including the stable π-system of aromatic rings is a great
challenge in organic synthesis. The coordination of transition
metals with aromatic rings1-7 and the addition of main group
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† Institute of Chemistry, CAS.
‡ Peking University.
§ Shanghai Institute of Organic Chemistry.
10.1021/jo070160u CCC: $37.00 © 2007 American Chemical Society
Published on Web 03/29/2007
3484
J. Org. Chem. 2007, 72, 3484-3491

Dearomatizing Cyclization and Skeletal Rearrangement
SCHEME 1. Dearomatizing Anionic Cyclization of
1-Lithio-4-naphthyl-1,3-butadienes Followed by Reaction
with Electrophiles: Formation of Spirocyclopentadiene
Derivatives
π-system of aromatic rings. In particular, the intramolecular
nucleophilic addition of organolithium to aromatic rings has
become one of the most efficient approaches to break the
π-system of arenes.12-17 A variety of functionalized bicyclic,
polycyclic, and spiro compounds can be thus prepared using
this approach. In principle, electron-deficient aromatic rings
bearing electron-withdrawing groups, such as carbonyl groups,
amides including N-benzyl benzamides, N-benzyl naphthamides,
sulfonamides, and phosphonamides, etc., are extensively studied
by the Clayden12-16 and Lopez-Ortiz groups17 because these
types of aromatic compounds can efficiently undergo nucleo-
philic attack leading to various useful compounds.11-17
Recently, we have communicated dearomatizing anionic
cyclization of 4-naphthyl 1-lithio-1,3-butadienes 2, which was
generated in situ quantitatively from their corresponding iodo
compounds 1 (Scheme 1).18 Several features of this reaction
can be depicted as follows. (1) This reaction at -78 °C resulted
in the formation of the spirocyclopentadiene intermediates 3,
obviously via ipso intramolecular nucleophilic attack, which is
rarely observed in dearomatization reactions.2,5,15 The commonly
obtained fused ring products 4 and related compounds via vicinal
attack were not formed at all under the reaction conditions.
Furthermore, the dearomatized organolithium intermediates 3
can react with a variety of electrophiles to afford spiro tricyclic
compounds 5 with different substituents. (2) The butadienyl-
lithium (sp2C-Li) as a nucleophile to attack the aromatic rings
is unprecedented. It is of special interest because the useful
butadienyl skeleton can be integrated with the aromatic rings.
(3) The aromatic ring (here naphthalene) is unactivated. Fewer
examples are known for dearomatization of unactivated aromatic
rings.15,19
During our further investigation into this unique reaction, we
found that, in addition to the naphthyl ring in 4-naphthyl 1-lithio-
1,3-butadienes 2, the phenyl ring in 4-phenyl 1-lithio-1,3-
butadienes could also undergo the dearomatizing anionic
cyclization. More interestingly, we found that the kinetically
favored ipso attack intermediates underwent a novel thermal
skeletal rearrangement to afford the vicinal products, tetrasub-
stituted phenanthrenes, via a dearomatization/1,2-alkyl shift/
rearomatization process. In this paper, we report the scope and
limitations of this synthetically useful reaction.
(2) (a) Chamberlin, S.; Wulff, W. D. J. Am. Chem. Soc. 1992, 114,
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2004, 69, 1161-1168. (c) Pigge, F. C.; Coniglio, J. J.; Fang, S. Organo-
metallics 2002, 21, 4505-4512.
(6) A lanthanocene-induced dearomatization of a pendent phenyl ring
was reported: Liu, R.; Zhang, C.; Zhu, Z.; Luo, J.; Zhou, X.; Weng, L.
Chem.sEur. J. 2006, 12, 6940-6952.
(7) Photoirradiation of Mn-arene complexes: Zhou, L.; Wu, L.-Z.;
Zhang, L.-P.; Tung, C.-H. Organometallics 2006, 25, 1707-1711 and
references therein.
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59-67. (b) Bailey, W. F.; Jiang, X. ARKIVOC 2006, 6, 25-32.
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N. Tetrahedron 2006, 62, 6182-6189.
(11) (a) Maruoka, K.; Ito, M.; Yamamoto, H. J. Am. Chem. Soc. 1995,
117, 9091-9092. (b) Plunian, B.; Mortier, J.; Vaultier, M.; Touper, L. J.
Org. Chem. 1996, 61, 5206-5207. (c) Kolotuchin, S. V.; Meyser, A. I. J.
Org. Chem. 2000, 65, 3018-3020. (d) Tomioka, K.; Shioya, Y.; Nagaoka,
Y.; Yamada, K. I. J. Org. Chem. 2001, 66, 7051-7054. (e) Nishiwaki, K.;
Ogawa, T.; Matsuo, K. Angew. Chem., Int. Ed. 2002, 41, 484-486.
(12) For recent reviews on cyclizations of organolithiums onto aromatic
rings, see: (a) Clayden, J.; Kenworthy, M. N. Synthesis 2004, 1721-1736.
(b) Clayden, J. Organolithiums: SelectiVity for Synthesis; Tetrahedron
Organic Chemistry Series; Pergamon: Oxford, 2002; Vol. 23, pp 282-
335.
(13) (a) Clayden, J.; Turnbull, R.; Pinto, I. Org. Lett. 2004, 6, 609-
611. (b) Clayden, J.; Turnbull, R.; Helliwell, M.; Pinto, I. Chem. Commun.
2004, 2430-2431. (c) Clayden, J.; Knowles, F. E.; Baldwin, I. R. J. Am.
Chem. Soc. 2005, 127, 2412-2413. (d) Clayden, J.; Turnbull, R.; Pinto, I.
Tetrahedron: Asymmetry 2005, 16, 2235-2241.
(14) (a) Clayden, J.; Hamilton, S. D.; Mohammed, R. T. Org. Lett. 2005,
7, 3673-3676. See also: (b) Fraenkel, G.; Ho, C. C.; Liang, Y.; Yu, S. J.
Am. Chem. Soc. 1972, 94, 4732-4734. (c) Foos, J.; Steel, F.; Rizvi, S. Q.
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(15) Clayden, J.; Kenworthy, M. N. Org. Lett. 2002, 4, 787-790.
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tization and photochemical process, see: Clayden, J.; Knowles, F. E.; Menet,
C. J. J. Am. Chem. Soc. 2003, 125, 9278-9279.
Results and Discussion
Intramolecular Dearomatizing ipso Attack of Butadienyl-
lithium to Naphthyl Rings in 4-Naphthyl 1-Lithio-1,3-
butadienes and to Phenyl Rings in 4-Phenyl 1-Lithio-1,3-
butadienes, Affording Spirocyclopentadiene Derivatives and
Further C-C Bond Forming Applications. 4-Aryl 1-lithio-
1,3-butadiene derivatives used in this research, including
4-naphthyl, 4-phenyl, and 4-(substituted phenyl) 1-lithio-1,3-
butadiene derivatives, were quantitatively generated in situ from
their corresponding 4-aryl 1-iodo-1,3-butadienes by lithium-
halogen exchange with t-BuLi. 4-Aryl 1-iodo-1,3-butadiene
derivatives could be readily prepared in high isolation yields in
one pot from alkynes and aryl halides mediated by the
cooperation of low-valent zirconocene species with copper
salts.20 Thus, when 1-iodo-4-naphthyl-1,3-butadiene 1a (R )
Et) was treated with 2 equiv of t-BuLi at -78 °C, no formation
of the corresponding monolithio reagent 2 was observed upon
hydrolysis with aqueous NaHCO3 at -78 °C. Instead, we
(17) (a) Ramallal, A. M.; Fernandez, I.; Lopez-Ortiz, F.; Gonzalez, J.
Chem.sEur. J. 2005, 11, 3022-3031 and references therein. See also: (b)
Fernandez, I.; Gomez, G. R.; Alfonso, I.; Iglesias, M. J.; Lopez-Ortiz, F.
Chem. Commun. 2005, 5408-5410. (c) Fernandez, I.; Lopez-Ortiz, F. Chem.
Commun. 2004, 1142-1243. (d) Fernandez, I.; Gonzalez, J.; Lopez-Ortiz,
F. J. Am. Chem. Soc. 2004, 126, 12551-12564. (e) Fernandez, I.; Forcen-
Acebal, A.; Lopez-Ortiz, F.; Garcia-Granda, S. J. Org. Chem. 2003, 68,
4472-4485.
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1994, 50, 7177-7192.
(20) Takahashi, T.; Sun, W.; Xi, C.; Ubayama, H.; Xi, Z. Tetrahedron
1998, 54, 715-726.
(18) Wang, Z.; Xi, Z. Synlett 2006, 1275-1277.
J. Org. Chem, Vol. 72, No. 9, 2007 3485

Liu et al.
TABLE 1. Spirocyclopentadiene Products from Dearomatizing
Anionic Cyclization of 1-Lithio-4-naphthyl-1,3-butadienes Followed
by Reactions with Electrophilesa
FIGURE 1. A variety of 4-phenyl 1-iodo-1,3-butadienes used in this
research.
mixture of separable double bond positional isomers (5j and
5j′), while ketones gave only one product (5k). When 1d was
used, the tetracyclic spiro compounds (5l, 5m, 5n) could be
obtained in high yields.
It should be mentioned that at this temperature only the ipso
attack products, the spiro compounds 5 and/or 5′, were obtained.
The usually observed vicinal intramolecular nucleophilic attack
products were not observed at all.
Prompted by the unusual reaction of 4-naphthyl 1-lithio-1,3-
butadienes, we investigated the reaction of analogous 4-phenyl
1-lithio-1,3-butadiene derivatives. Listed in Figure 1 are 4-phen-
yl 1-iodo-1,3-butadienes used in this research.20 These com-
pounds were prepared following the literature procedure and
could be obtained in high isolated yields.20 They can be readily
transformed to their corresponding 4-phenyl 1-lithio-1,3-buta-
diene derivatives via lithium-iodo exchange when they were
subject to reactions.
Initially, as shown in Scheme 2, we carried out the reaction
of 6a with 2 equiv of t-BuLi at -78 °C. We did observe the
lithium-iodo exchange affording the hydrolyzed product 8a in
95% isolated yield upon quench with aqueous NaHCO3.
However, on the contrary, this monolithium reagent 7 was stable
at -78 °C. Totally no dearomatizing anionic cyclization took
place. It was also stable even at -50 °C. This is in sharp contrast
to the reactivity of 2 as described above. We then increased the
reaction temperature to 0 °C, and we found dearomatizing
anionic cyclization took place and completed after 2 h at this
temperature. Hydrolysis of the reaction mixture with aqueous
NaHCO3 afforded a mixture of two double bond positional
isomers 10a and 10a′ in 40 and 36% isolated yields, respec-
tively.
a Isolated yields. b Hydrolyzed mixture of products using aqueous
NaHCO3. c From allyl bromide. d From benzyl bromide. e From t-BuCOCl.
f From AdCOCl. g From CO2, hydrolyzed using aqueous NH4Cl. Structure
was determined by X-ray crystal analysis. h From SiMe3Cl. i Reaction with
PhCHO followed by quench using aqueous NaHCO3. j From cyclohexanone.
isolated the spiro tricyclic products 5a and 5a′ as double bond
positional isomers (5a: 69% yield, 5a′: 21% yield) in 90%
combined yield (Table 1). This result indicated that the in situ
generated 4-naphthyl 1-lithio-1,3-butadiene 2a was very reactive
even at -78 °C to undergo the unusual dearomatizing anionic
cyclization, forming the type of anionic species 3 as shown in
Scheme 1.
As demonstrated in Table 1, 4-naphthyl 1-iodo-1,3-butadiene
derivatives 1a-d could all undergo this rapid sequential
lithium-iodo exchange/dearomatizing anionic cyclization pro-
cess to give the anionic species 3. These corresponding lithiated
intermediates 3 could be applied further to form new C-C bonds
with a variety of electrophiles. Very interestingly, depending
on the nature of electrophiles, either a mixture of regioisomers
or a sole product of high regioselectivity was obtained, all in
excellent isolated yields. For example, electrophiles such allyl
bromide (5b), benzyl bromide (5c), acid chlorides (5d, 5e, 5f),
CO2 (5g), and Me3SiCl (5h, 5i) gave only one product. Ketones
and aldehydes could also be applied, but aldehydes afforded a
It should be mentioned that at this temperature the usually
observed vicinal intramolecular nucleophilic attack products of
the type 11a or related compounds were not observed at all.
To further demonstrate the usefulness of this reaction, we
treated the lithiated intermediates 9 with a variety of electro-
philes. Shown in Table 2 are examples obtained from the
reaction of 9a with aldehydes, ketones, and imine PhCHdNPh.
Representative structures are given as 12 and 12′. All products
were obtained in good isolation yields. Although mixtures of
double bond positional isomers were obtained (entries 1-8),
3486 J. Org. Chem., Vol. 72, No. 9, 2007

Dearomatizing Cyclization and Skeletal Rearrangement
TABLE 2. Treatment of the Reaction Mixture 9a with
Electrophiles
SCHEME 2. Dearomatizing Anionic Cyclization of
1-Lithio-4-phenyl-1,3-butadienes Followed by Reaction with
Electrophiles: Formation of Spirocyclopentadiene
Derivatives
they could be easily separated using column chromatography.
In the case of bulky t-BuCHO (entry 9), only the isomer 12j′
was formed. For the reaction of 9a with ketones and PhCHd
NPh (entries 10-12), isomers 12′ were generally obtained,
probably due to steric effect.
We then applied other 4-phenyl 1-lithio-1,3-butadiene deriva-
tives which could be readily generated in situ from their
corresponding 4-phenyl 1-iodo-1,3-butadienes (6b-j) given in
Figure 1. Results are shown in Figure 2. As expected, 4-phenyl
1-lithio-1,3-butadiene derivatives (6b-d) reacted with alde-
hydes, ketones, and/or PhCHdNPh in a similar manner
compared with 6a, but the substituted phenyl rings behaved
differently from each other. For example, the o-methyl phenyl
ring 6e underwent the intramolecular nucleophilic attack
similarly with the nonsubstituted phenyl rings 6a-d, affording
19 in 57% isolated yield from its reaction with cyclopen-
tanenone. The m-methyl phenyl ring (6f) could also undergo
the reaction. However, the p-substituted phenyl rings (6g: Me,
6h: I, 6i: CF3) did not show any cyclization reactions, even in
the case of the very strong electron-withdrawing group CF3.
These results demonstrate that the electronic effect, which makes
the phenyl ring more electron-deficient, may not be the major
reason for the dearomatizing anionic cyclization. The steric
effect and the stability of the thus generated dearomatized
species are assumed to be the major factors. In addition, the
thienyl iodobutadiene 6j could undergo the lithium-iodo
exchange, but no dearomatizing cyclization took place even in
refluxing toluene.
Formation of Tetrasubstituted Phenanthrene Derivatives
via Novel Skeletal Rearrangement of the ipso Attack
Intermediates Followed by Rearomatization. As described
above, the dearomatization cyclization took place very fast even
at -78 °C for 4-naphthyl 1-lithio-1,3-butadienes. In the case
of 4-phenyl 1-lithio-1,3-butadienes, the dearomatization cy-
clization proceeded relatively slowly and a higher temperature
(0 °C) was required. In order to investigate whether or not these
types of compounds can undergo the commonly observed vicinal
attack to afford the fused ring compounds, such as tetrasubsti-
tuted phenanthrene derivatives,21-25 we screened reaction condi-
tions. Initially, we used toluene as the solvent and carried out
the reaction of 1a with 2 equiv of t-BuLi from lower temper-
atures to 75 °C. Surprisingly, when the reaction mixture was
stirred at 75 °C for 3 h, the desired product, tetraethyl-substituted
FIGURE 2. More examples of spirocyclopentadienes using 6b-f
(isolated yields).
J. Org. Chem, Vol. 72, No. 9, 2007 3487

Liu et al.
TABLE 3. Preparation of Substituted Phenanthrene Derivatives
21
SCHEME 3. Formation of Tetraethyl Phenanthrene
Derivative 21a: Solvent Effect
phenanthrene derivative 21a, was indeed formed in 55% isolated
yield (Scheme 3). In addition to the expected 21a, an unexpected
product, the tert-butylated 5oa was also obtained in 19% isolated
yield. Due to the formation of 5oa, the expected 21a was formed
in unsatisfactory yields. The formation of 5oa can be explained
by that the in situ generated t-BuI from 1a and t-BuLi does not
react smoothly enough with another molecule of t-BuLi in
toluene to get consumed. Thus, the later generated dearomatized
lithiated intermediates 3 are trapped partially by the remaining
t-BuI to afford the tert-butylated 5oa.
To increase the yield of 21a, the formation of 5oa should be
avoided. From the above analysis, we tried to use more polar
solvents including mixed solvents to promote the complete and
fast consumption of the in situ generated t-BuI. Finally, as shown
in Scheme 3, we found when a 1:1 mixed solvent of diethyl
ether and toluene was used and the reaction mixture of
4-naphthyl 1-iodo-1,3-butadiene 1a and t-BuLi was heated up
to 75 °C the phenanthrene derivative 21a was formed very
a A: Toluene/Et2O ) 1:1; B: Toluene. b Isolated yield.
cleanly and obtained in 91% isolated yield. Formation of the
tert-butylated 5oa was completely suppressed. Listed in Table
3 are representative results of phenanthrene derivatives obtained
in the above-described two different conditions, and the forma-
tion of 5o is also given for comparison. Substituted phenanthrene
derivatives can be thus prepared in excellent isolated yields.
These types of fused ring compounds are very important and
have attracted much recent attention as new organic materials.21-25
This reaction provides an efficient method for these types of
compounds.
(21) For reviews on preparation of substituted naphthalenes, see: (a) de
Koning, C. B.; Rousseau, A. L.; van Otterlo, W. A. L. Tetrahedron 2003,
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A.; Nakajima, K.; Takahashi, T. Org. Lett. 2005, 7, 5453-5456. (g)
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2003, 5, 4121-4123. (d) Yasukawa, T.; Satoh, T.; Miura, M.; Nomura, M.
J. Am. Chem. Soc. 2002, 124, 12680-12681. (e) Larock, R. C.; Tian, Q. J.
Org. Chem. 1998, 63, 2002-2009. (f) Larock, R. C.; Doty, M. J.; Tian,
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What interested us much more was how the vicinal attack
products, the tetrasubstituted phenanthrenes 21, were generated
from the reaction mixture. As we mentioned above, the ipso
attack of 4-naphthyl 1-lithio-1,3-butadienes took place very
easily even at -78 °C. The formation of the phenanthrene
derivatives 21 was really a surprise to us, though it was what
we expected. Obviously, the formation of phenanthrene deriva-
tives 21 was under thermodynamic control. Thus we carried
out a series of experiments to obtain evidence.
To obtain direct experimental evidence, we carried out the
reactions and analyzed the products at different reaction
temperatures. First, we used toluene as the solvent; this was
aimed at, in addition to understanding the mechanism for the
formation of phenanthrene derivatives 21, ensuring the formation
of the tert-butylated 5o. As can be seen from Table 4, when
the reaction was carried out in toluene at -78 °C for 2 h (entry
1), half of the starting monoiodo compound 1a remained
unlithiated, indicating that the solvent is crucial for the lithiation
reaction. On the other hand, this result also demonstrated that
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J. J. Org. Chem. 2006, 71, 7780-7784. (b) Harrowven, D. C.; Guy, I. L.;
Nanson, L. Angew. Chem., Int. Ed. 2006, 45, 2242-2245. (c) Takahashi,
T.; Li, Y.; Stepnicka, P.; Kitamura, M.; Liu, Y.; Nakajima, K.; Kotora, M.
J. Am. Chem. Soc. 2002, 124, 576-582. (d) Qiao, X.; Ho, D. M.; Pascal,
R. A., Jr. Angew. Chem., Int. Ed. Engl. 1997, 36, 1531-1532.
3488 J. Org. Chem., Vol. 72, No. 9, 2007

Dearomatizing Cyclization and Skeletal Rearrangement
TABLE 4. Investigation into the Reaction Mechanisms:
Temperature-Variational Experiment in Toulene
TABLE 5. Investigation into the Reaction Mechanisms:
Temperature-Variational Experiment in Toluene/Ether
Yield of Product %a
Yield of Product %a
T
(°C)
time
(h)
T
(°C)
time
(h)
entry
(5a+5a′)b
21a
entry
1a
5a+5a′
21a
5oa
1
2
3
4
5
6
7
-78
0
rt
50
50
75
75
1
2
3
1
2
1
3
89
91
86
39
18
trace
trace
0
0
1
2
3
4
5
6
7
-78
0
rt
50
50
75
75
2
1
3
1
3
1
3
54
0
0
0
0
29
46
29
21
6
2
11
22
32
54
59
57(55)
9
33
33
35
31
28
29(19)
<3
44
67
90
91
0
0
6
6
a Isolated yields. b A mixture of 5a and 5a′ in 1:0.3 molar ratio. Combined
isolated yields.
a GC yields. Isolated yields are given in parentheses.
SCHEME 4. Skeletal Rearrangement of the Spiro
Intermediates to Form the Fused Ring Compounds
even in toluene, once 4-naphthyl 1-lithio-1,3-butadienes 2 were
formed, dearomatization cyclization took place immediately at
-78 °C. In addition to the dearomatization products 5a and
5a′ in 29% yield, the tert-butylated 5oa was also already formed
in 9% yield. After the reaction temperature was increased to 0
°C for 1 h (entry 2), the starting monoiodo compound 1a
disappeared, affording 46% of the dearomatization products 5a
and 5a′ and 33% of 5oa. At this temperature, the phenanthrene
derivative 21a appeared and was obtained in 11% yield. When
the reaction temperature was further increased to room tem-
perature, 50 °C, and higher (entries 3-7), the dearomatization
products 5a and 5a′ disappeared gradually, while the phenan-
threne derivative 21a became the major product. Under these
conditions, the yield of the tert-butylated 5oa became steady
around 30%. This result indicated that t-BuI was quickly
consumed at over 0 °C even in toluene.
The temperature-dependent experiments in the mixed solvent
(toluene/diethyl ether ) 1:1) gave more instructive information
for the formation of the phenanthrene derivative 21a from the
dearomatization products (5a and 5a′). As shown in Table 5,
the dearomatization products (5a and 5a′) were formed cleanly
at -78 °C within 1 h and obtained in excellent isolated yields.
This result also demonstrated that the lithium-iodo exchange
reaction in this mixed solvent proceeded smoothly. At over room
temperature, the phenanthrene derivative 21a appeared, while
the dearomatization products decreased. At 50 °C for 1 h, more
than half of the dearomatization products were transformed to
the phenanthrene derivative 21a (entry 4). When the reaction
temperature was increased to 75 °C for 1 h, the dearomatization
products disappeared completely, resulting in the phenanthrene
derivative 21a in excellent isolated yields (entries 6 and 7).
Under these reaction conditions, the above-mentioned 5oa was
not observed at all.
butadienes 2 solely undergo the kinetically favored ipso attack
to form the lithiated dearomatized intermediates 3, which are
thermally unstable. At temperatures higher than room temper-
ature, these intermediates 3 undergo a novel skeletal rearrange-
ment via 1,2-alkyl shift (intermediates 22) to afford the formally
vicinal attack lithiated dearomatized intermediates 4, which are
thermally unstable and generate the stable phenanthrene deriva-
tives via the rearomatization process.
For 4-phenyl 1-lithio-1,3-butadienes, this novel rearrangement
could not happen, although at reflux of toluene, the spiro
intermediates 9 gave mixtures of unknown products.
The above results revealed that the kinetically favored ipso
attack intermediates 3 might undergo thermodynamically con-
trolled skeletal rearrangement to afford the final tetrasubstituted
phenanthrenes 21. A proposed reaction mechanism is given in
Scheme 4. The in situ generated 4-naphthyl 1-lithio-1,3-
Conclusions
We have described the highly efficient and selective intramo-
lecular nucleophilic addition of the butadienyllithium to the
J. Org. Chem, Vol. 72, No. 9, 2007 3489

Liu et al.
1H, OH), 1.47-1.87 (m, 12H, CH2), 2.08-2.36 (m, 6H, CH2), 3.55
(d, J ) 2.7 Hz, 1H, CH), 5.13 (dd, J ) 10.2, 1.5 Hz, 1H, CH),
6.09 (dd, J ) 10.5, 4.2 Hz, 1H, CH), 6.61 (dd, J ) 7.8, 1.5 Hz,
1H, CH), 6.93-6.98 (m, 1H, CH), 7.04-7.09 (m, 1H, CH), 7.25-
7.55 (m, 1H, CH); 13C NMR (75 MHz, CDCl3, TMS) δ 14.67 (1
CH3), 14.92 (1 CH3), 15.26 (1 CH3), 15.73 (1 CH3), 18.86 (1 CH2),
18.90 (1 CH2), 18.92 (1 CH2), 19.39 (1 CH2), 21.77 (1 CH2), 22.03
(1 CH2), 25.79 (1 CH2), 33.69 (1 CH2), 35.98 (1 CH2), 49.05 (1
CH), 63.47 (1 quart C), 75.00 (1 quart C), 125.15 (1 CH), 125.54
(1 CH), 125.99 (1 CH), 127.29 (1 CH), 130.12 (1 CH), 130.85 (1
CH), 134.55 (1 quart C), 135.99 (1 quart C), 140.50 (1 quart C),
143.51 (1 quart C), 149.86 (1 quart C), 150.92 (1 quart C). HRMS
calcd for C28H38O: 390.2923, found 390.2926.
aromatic rings, resulting in full dearomatization of phenyl rings
and partial dearomatization of naphthyl rings via ipso attack.
A wide variety of multiply substituted bicyclic and polycyclic
spirocyclopentadienes and phenanthrene derivatives could be
readily prepared by further treatment of the in situ generated
lithiated dearomatized intermediates. Mechanistic studies re-
vealed interesting reactivity of the ipso attack dearomatized
intermediates from 4-naphthyl 1-lithio-1,3-butadienes. These
ipso attack intermediates undergo a novel skeletal rearrangement
via a 1,2-alkyl shift followed by rearomatization to afford the
formally vicinal attack products phenanthrene derivatives.
5n: Colorless liquid, isolated yield 71% (127 mg); 1H NMR (300
MHz, CDCl3, TMS) δ 0.67-0.76 (m, 6H, CH3), 1.04-1.25 (m,
4H, CH2), 1.64-2.06 (m, 8H, CH2), 2.39-2.65 (m, 6H, CH2),
3.55-3.58 (m, 1H, CH), 5.00-5.07 (m, 3H, CH2 and CH), 5.77-
5.91 (m, 1H, CH), 5.95 (dd, J ) 10.2, 3.6 Hz, 1H, CH), 6.53-
6.56 (m, 1H, CH), 6.90-6.95 (m, 1H, CH), 7.07-7.12 (m, 1H,
CH), 7.22-7.25 (m, 1H, CH); 13C NMR (75 MHz, CDCl3, TMS)
δ 14.43 (1 CH3), 14.58 (1 CH3), 22.17 (1 CH2), 22.49 (1 CH2),
23.84 (1 CH2), 23.86 (1 CH2), 24.38 (1 CH2), 24.40 (1 CH2), 28.57
(1 CH2), 28.66 (1 CH2), 37.87 (1 CH), 43.80 (1 CH2), 63.34 (1
quart C), 116.50 (1 CH2), 125.50 (1 CH), 125.84 (1 CH), 126.94
(1 CH), 127.92 (1 CH), 128.02 (1 CH), 128.56 (1 CH), 134.73 (1
quart C), 136.32 (1 CH), 136.91 (1 quart C), 137.34 (1 quart C),
137.85 (1 quart C), 147.37 (1 quart C), 147.83 (1 quart C). HRMS
calcd for C27H34: 358.2660, found 358.2660.
Typical Procedure for the Preparation of Spirocyclopenta-
diene Products 10a, 10a′, 12a-l, and 13-20 from Dearomatizing
Anionic Cyclization of 4-Phenyl 1-Lithio-1,3-butadienes Fol-
lowed by Reactions with Electrophiles. To a diethyl ether (5 mL)
solution of 4-phenyl 1-iodo-1,3-butadiene 6 (0.5 mmol) at -78 °C
was added t-BuLi (1.0 mmol, 1.5 M in pentane). The above reaction
mixture was first stirred at -78 °C for 1 h. Hydrolysis of the
reaction mixture of 6a with saturated aqueous NaHCO3 afforded
8a in 95% isolated yield.20 When the reaction temperature of 6
was allowed to warm up to 0 °C and kept at this temperature for
2 h, hydrolysis of the reaction mixture of 6a with saturated aqueous
NaHCO3 afforded a mixture of two products 10a and 10a′, which
could be separated using column chromatography to give pure 10a
and pure 10′ in 40 and 36% isolated yields, respectively.
After the above reaction mixture of 6 was stirred at 0 °C for 2
h, instead of being quench with saturated aqueous NaHCO3, the
reaction mixture was further treated with an electrophile (0.6 mmol)
at 0 °C for 2 h. The reaction mixture was then quenched with
aqueous NaHCO3. The layers were separated, and the aqueous phase
was extracted three times with ether. The combined extracts were
washed with brine and dried over MgSO4. Evaporation under
reduced pressure gave crude products 12-20, which were purified
by flash chromatography.
Experimental Section
Typical Procedure for the Preparation of Spirocyclopenta-
diene Products 5a-n from Dearomatizing Anionic Cyclization
of 4-Naphthyl 1-Lithio-1,3-butadienes Followed by Reactions
with Electrophiles. To a diethyl ether (5 mL) solution of 4-naphthyl
1-iodo-1,3-butadiene 1 (0.5 mmol) at -78 °C was added t-BuLi
(1.0 mmol, 1.5 M in pentane). The above reaction mixture was
then stirred at -78 °C for 1 h. Hydrolysis of the reaction mixture
of 1a with saturated aqueous NaHCO3 afforded a mixture of two
products 5a and 5a′, which were separated using column chroma-
tography to give pure 5a and pure 5a′ in 69 and 21% isolated yields,
respectively.
When the above reaction mixture of 1 was further treated with
an electrophile (0.6 mmol) instead of being quenched with saturated
aqueous NaHCO3, the reaction mixture was continuously stirred
at -78 °C for another 1 h and then quenched with aqueous
NaHCO3. The layers were separated, and the aqueous phase was
extracted three times with ether. The combined extracts were
washed with brine and dried over MgSO4. Evaporation under
reduced pressure gave a crude product 5b-n, which was purified
by flash chromatography.
5c: Colorless liquid, isolated yield 84% (160 mg); 1H NMR (300
MHz, CDCl3, TMS) δ 0.63-0.79 (m, 6H, CH3), 1.07-1.13 (m,
6H, CH3), 1.82-2.04 (m, 4H, CH2), 2.23-2.32 (m, 4H, CH2), 2.80
(dd, J ) 13.2, 9.6 Hz, 1H, CH2), 3.27 (dd, J ) 13.2, 4.8 Hz, 1H,
CH2), 3.77 (t, J ) 4.5 Hz, 1H, CH), 4.98 (dd, J ) 10.2, 1.5 Hz,
1H, CH), 5.80 (dd, J ) 10.2, 3.6 Hz, 1H, CH), 6.58 (d, J ) 7.8
Hz, 1H, CH), 6.95 (t, J ) 7.2 Hz, 1H, CH), 7.10-7.31 (m, 7H,
CH); 13C NMR (75 MHz, CDCl3, TMS) δ 14.86 (1 CH3), 15.02 (1
CH3), 15.12 (1 CH3), 15.39 (1 CH3), 18.87 (1 CH2), 18.93 (1 CH2),
19.16 (1 CH2), 19.33 (1 CH2), 40.13 (1 CH), 46.46 (1 CH2), 62.94
(1 quart C), 125.70 (1 CH), 125.83 (1 CH), 126.02 (1 CH), 127.14
(1 CH), 127.54 (1 CH), 128.16 (2 CH), 128.24 (1 CH), 128.73 (1
CH), 129.52 (2 CH), 134.73 (1 quart C), 137.90 (1 quart C), 139.83
(1 quart C), 141.70 (1 quart C), 142.02 (1 quart C), 150.14 (1 quart
C), 150.54 (1 quart C). HRMS calcd for C29H34: 382.2661, found
382.2657.
5f: Colorless liquid, isolated yield 60% (170 mg); 1H NMR (300
MHz, CDCl3, TMS) δ 0.70-0.78 (m, 6H, CH3), 0.86-1.00 (m,
6H, CH3), 1.05-2.27 (m, 39H, CH2 and CH), 5.06-5.12 (m, 2H,
CH), 5.84 (dd, J ) 10.2, 3.6 Hz, 1H, CH), 5.57 (dd, J ) 7.8, 1.5
Hz, 1H, CH), 6.80-7.05 (m, 3H, CH); 13C NMR (75 MHz, CDCl3,
TMS) δ 13.84 (1 CH3), 13.99 (1 CH3), 14.08 (2 CH3), 23.08 (1
CH2), 23.12 (1 CH2), 23.14 (2 CH2), 25.89 (3 CH2), 26.31 (1 CH2),
28.03 (3 CH), 32.09 (1 CH2), 32.52 (1 CH2), 32.55 (1 CH2), 32.61
(1 CH2), 36.58 (3 CH2), 38.30 (3 CH2), 47.21 (1 CH), 47.46 (1
quart C), 62.65 (1 quart C), 121.62 (1 CH), 126.10 (1 CH), 126.30
(1 CH), 126.96 (1 CH), 128.32 (1 CH), 131.55 (1 CH), 134.22 (1
quart C), 135.44 (1 quart C), 141.21 (1 quart C), 141.29 (1 quart
C), 148.63 (1 quart C), 149.94 (1 quart C), 213.55 (1 quart C); IR
(neat) ν (CdO) ) 1708 cm-1. HRMS calcd for C41H58O: 566.4488,
found 566.4481.
10a: Colorless liquid, isolated yield 40% (48 mg); 1H NMR (300
MHz, CDCl3, TMS) δ 1.01-1.08 (m, 12H, CH3), 2.11-2.28 (m,
8H, CH2), 2.32 (d, J ) 1.8 Hz, 2H, CH2), 4.84-4.87 (m, 1H, CH),
5.89-5.90 (m, 2H, CH), 5.96-6.01 (m, 1H, CH); 13C NMR (75
MHz, CDCl3, TMS) δ 15.08 (2 CH3), 15.50 (2 CH3), 18.71 (2 CH2),
18.89 (2 CH2), 28.02 (1 CH2), 56.50 (1 quart C), 122.53 (1 CH),
122.80 (1 CH), 126.29 (1 CH), 129.70 (1 CH), 140.61 (2 quart C),
148.70 (2 quart C). HRMS calcd for C18H26: 242.2034, found
242.2034.
1
10a′: Colorless liquid, isolated yield 36% (44 mg); H NMR
(300 MHz, CDCl3, TMS) δ 0.99 (t, J ) 7.5 Hz, 6H, CH3), 1.05 (t,
J ) 7.5 Hz, 6H, CH3), 2.12 (q, J ) 7.5 Hz, 4H, CH2), 2.23 (q, J
) 7.5 Hz, 4H, CH2), 2.73-2.76 (m, 2H, CH2), 4.94-4.98 (m, 2H,
CH), 5.87-5.92 (m, 2H, CH); 13C NMR (75 MHz, CDCl3, TMS)
δ 15.09 (2 CH3), 15.56 (2 CH3), 18.96 (2 CH2), 19.17 (2 CH2),
25.93 (1 CH), 60.57 (1 quart C), 124.49 (2 CH), 128.43 (2 CH),
141.64 (2 quart C), 148.09 (2 quart C). HRMS calcd for C18H26:
242.2034, found 242.2034.
5k: Colorless liquid, isolated yield 82% (160 mg); 1H NMR (300
MHz, CDCl3, TMS) δ 0.53 (t, J ) 7.5 Hz, 3H, CH3), 0.90 (t, J )
7.5 Hz, 3H, CH3), 1.06-1.16 (m, 6H, CH3), 1.27 (d, J ) 8.7 Hz,
3490 J. Org. Chem., Vol. 72, No. 9, 2007

Dearomatizing Cyclization and Skeletal Rearrangement
1
12k′: Colorless liquid, isolated yield 50% (106 mg); H NMR
(300 MHz, CDCl3, TMS) δ 0.94-1.07 (m, 12H, CH3), 2.03-2.26
(m, 8H, CH2), 2.48 (s, 1H, OH), 4.16-4.19 (m, 1H, CH), 5.15
(dd, J ) 10.2, 2.1 Hz, 2H, CH), 5.66 (dd, J ) 10.5, 2.7 Hz, 2H,
CH), 7.16-7.21 (m, 2H, CH), 7.29-7.34 (m, 4H, CH), 7.59-7.62
(m, 4H, CH); 13C NMR (75 MHz, CDCl3, TMS) δ 14.97 (1 CH3),
15.08 (1 CH3), 15.69 (1 CH3), 15.77 (1 CH3), 18.93 (1 CH2), 18.95
(1 CH2), 19.05 (1 CH2), 19.12 (1 CH2), 43.74 (1 CH), 61.10 (1
quart C), 78.79 (1 quart C), 124.74 (2 CH), 125.87 (4 CH), 126.52
(2 CH), 128.20 (4 CH), 132.88 (2 CH), 142.52 (1 quart C), 143.06
(1 quart C), 145.89 (2 quart C), 146.24 (1 quart C), 146.86 (1 quart
C). HRMS calcd for C31H36O: 424.2766, found 424.2777.
butadienes. To a mixed solvent of diethyl ether (2.5 mL) and
toluene (2.5 mL) or a toluene solution of 4-naphthyl 1-iodo-1,3-
butadiene 1 (0.5 mmol) at -78 °C was added t-BuLi (1.0 mmol,
1.5 M in pentane). After being stirred at -78 °C for 1 h, the above
reaction mixture was heated up to 75 °C and kept at this temperature
for 3 h. The reaction was then cooled down to room temperature
and was quenched with saturated aqueous NaHCO3. The layers were
separated, and the aqueous phase was extracted three times with
ether. The combined extracts were washed with brine and dried
over MgSO4. Evaporation under reduced pressure followed by flash
chromatography afforded the title product. In the case of the mixed
solvent of diethyl ether (2.5 mL) and toluene (2.5 mL), tetrasub-
stituted phenanthrene products 21a-d were obtained as the only
products. In the case of toluene as the solvent, in addition to 21a-
d, spirocyclopentadienes 5oa-c were also obtained. The tetrasub-
stituted phenanthrene product 21 and the spirocyclopentadiene 5o
could be readily separated by column chromatography.
1
12l′: Colorless liquid, isolated yield 77% (163 mg); H NMR
(300 MHz, CDCl3, TMS) δ 0.85-1.26 (m, 12H, CH3), 1.99-2.34
(m, 8H, CH2), 3.34, (dd, J ) 5.1, 2.7 Hz, 1H, CH), 4.30 (br, 1H,
NH), 4.48 (d, J ) 3.3 Hz, 1H, CH), 5.15-5.18 (m, 2H, CH), 5.62
(d, J ) 10.5 Hz, 1H, CH), 5.92 (d, J ) 9.0 Hz, 1H, CH), 6.44 (d,
J ) 8.4 Hz, 2H, CH), 6.58-6.63 (m, 1H, CH), 7.05 (t, J ) 7.5 Hz,
2H, CH), 7.19-7.40 (m, 5H, CH); 13C NMR (75 MHz, CDCl3,
TMS) δ 15.00 (1 CH3), 15.13 (1 CH3), 15.64 (1 CH3), 16.05 (1
CH3), 18.91 (1 CH2), 18.95 (1 CH2), 19.05 (1 CH2), 19.43 (1 CH2),
42.73 (1 CH), 60.70 (1 CH), 61.05 (1 quart C), 113.07 (2 CH),
116.98 (1 CH), 123.60 (1 CH), 126.82 (2 CH), 126.90 (1 CH),
128.18 (1 CH), 128.40 (2 CH), 129.06 (2 CH), 131.08 (1 CH),
131.93 (1 CH), 141.85 (1 quart C), 142.32 (1 quart C), 143.08 (1
quart C), 146.53 (1 quart C), 146.78 (1 quart C), 147.61 (1 quart
C). HRMS calcd for C31H37N: 423.2926, found 423.2871.
17: Colorless liquid, isolated yield 70% (187 mg); 1H NMR (300
MHz, CDCl3, TMS) δ 0.81-0.98 (m, 12H, CH3), 1.18-1.53 (m,
16H, CH2), 1.93-2.29 (m, 8H, CH2), 3.30 (dd, J ) 5.7, 2.7 Hz,
1H, CH), 4.26 (br, 1H, NH), 4.47 (d, J ) 3.6 Hz, 1H, CH), 5.11-
5.16 (m, 2H, CH), 5.60-5.64 (m, 1H, CH), 5.87-5.91 (m, 1H,
CH), 6.43 (d, J ) 7.8 Hz, 2H, CH), 6.62 (t, J ) 7.2 Hz, 1H, CH),
7.06 (dd, J ) 8.1, 7.5 Hz, 2H, CH), 7.24 (t, J ) 6.9 Hz, 1H, CH),
7.31-7.42 (m, 4H, CH); 13C NMR (75 MHz, CDCl3, TMS) δ 13.91
(1 CH3), 14.03 (1 CH3), 14.05 (1 CH3), 14.20 (1 CH3), 23.09 (1
CH2), 23.11 (1 CH2), 23.32 (1 CH2), 23.36 (1 CH2), 25.89 (1 CH2),
25.94 (1 CH2), 26.03 (1 CH2), 26.62 (1 CH2), 32.47 (1 CH2), 32.50
(1 CH2), 32.88 (1 CH2), 33.16 (1 CH2), 42.72 (1 CH), 61.03 (1
CH), 61.19 (1 quart C), 113.23 (2 CH), 117.02 (1 CH), 123.54 (1
CH), 126.90 (2 CH), 126.92 (1 CH), 128.07 (1 CH), 128.44 (2
CH), 129.02 (2 CH), 131.45 (1 CH), 132.14 (1 CH), 141.31 (1
quart C), 141.99 (1 quart C), 142.10 (1 quart C), 145.23 (1 quart
C), 145.74 (1 quart C), 147.69 (1 quart C).
1
21a: Colorless liquid, isolated yield 91% (132 mg); H NMR
(300 MHz, CDCl3, TMS) δ 1.21-1.28 (m, 6H, CH3), 1.34 (t, J )
7.5 Hz, 3H, CH3), 1.64 (t, J ) 7.2 Hz, 3H, CH3), 2.92 (q, J ) 7.5
Hz, 2H, CH2), 3.00 (q, J ) 7.5 Hz, 2H, CH2), 3.13 (q, J ) 7.5 Hz,
2H, CH2), 3.33-3.35 (m, 2H, CH2), 7.49-7.52 (m, 2H, CH), 7.61
(d, J ) 9.0 Hz, 1H, CH), 7.81-7.84 (m, 1H, CH), 7.92 (d, J ) 9.0
Hz, 1H, CH), 8.62-8.65 (m, 1H, CH); 13C NMR (75 MHz, CDCl3,
TMS) δ 15.86 (1 CH3), 15.88 (1 CH3), 16.10 (1 CH3), 16.31 (1
CH3), 22.29 (1 CH2), 22.53 (1 CH2), 22.72 (1 CH2), 25.27 (1 CH2),
123.33 (1 CH), 124.60 (1 CH), 125.33 (1 CH), 125.92 (1 CH),
127.75 (1 CH), 128.02 (1 CH), 129.80 (1 quart C), 130.14 (1 quart
C), 131.07 (1 quart C), 132.86 (1 quart C), 136.07 (1 quart C),
136.66 (1 quart C), 138.69 (1 quart C), 140.73 (1 quart C). HRMS
calcd for C22H26: 290.2034, found 290.2038.
1
21d: Colorless liquid, isolated yield 90% (142 mg); H NMR
(300 MHz, CDCl3, TMS) δ 1.08-1.20 (m, 6H, CH3), 1.62-2.07
(m, 8H, CH2), 2.96-3.17 (m, 8H, CH2), 7.48-7.51 (m, 2H, CH),
7.58 (d, J ) 9.0 Hz, 1H, CH), 7.80-7.83 (m, 1H, CH), 7.88 (d, J
) 9.0 Hz, 1H, CH), 8.46 (t, J ) 6.3 Hz, 1H, CH); 13C NMR (75
MHz, CDCl3, TMS) δ 14.30 (1 CH3), 14.83 (1 CH3), 22.66 (1 CH2),
22.99 (1 CH2), 23.22 (1 CH2), 23.76 (1 CH2), 27.66 (1 CH2), 27.70
(1 CH2), 30.75 (1 CH2), 34.71 (1 CH2), 123.17 (1 CH), 124.56 (1
CH), 125.34 (1 CH), 125.78 (1 CH), 127.79 (1 CH), 127.92 (1
CH), 129.34 (1 quart C), 129.57 (1 quart C), 131.12 (1 quart C),
132.88 (1 quart C), 134.17 (1 quart C), 134.50 (1 quart C), 135.38
(1 quart C), 136.41 (1 quart C). HRMS calcd for C24H28: 316.2191,
found 316.2200.
19: Colorless liquid, isolated yield 57% (97 mg); 1H NMR (300
MHz, CDCl3, TMS) δ 0.95-1.08 (m, 12H, CH3), 1.26 (t, J ) 1.5
Hz, 3H, CH3), 1.50 (br, 1H, OH), 1.64-1.88 (m, 8H, CH2), 1.94-
2.29 (m, 8H, CH2), 2.95-2.99 (m, 1H, CH), 5.04 (dd, J ) 9.9, 2.1
Hz, 1H, CH), 5.71-5.73 (m, 1H, CH), 5.86-5.90 (m, 1H, CH);
13C NMR (75 MHz, CDCl3, TMS) δ 14.77 (1 CH3), 14.96 (2 CH3),
15.05 (1 CH3), 17.97 (1 CH3), 18.96 (1 CH2), 19.00 (2 CH2), 19.04
(1 CH2), 23.87 (1 CH2), 23.91 (1 CH2), 38.20 (1 CH2), 38.32 (1
CH2), 46.80 (1 CH), 63.78 (1 quart C), 83.94 (1 quart C), 123.17
(1 CH), 124.80 (1 CH), 132.03 (1 CH), 136.48 (1 quart C), 142.96
(1 quart C), 143.64 (1 quart C), 145.61 (1 quart C), 146.16 (1 quart
C). HRMS calcd for C24H36O: 340.2766, found 340.2758.
Typical Procedure for the Preparation of Tetrasubstituted
Phenanthrene Products 21a-d from 4-Naphthyl 1-Lithio-1,3-
Acknowledgment. This work was supported by the Natural
Science Foundation of China and the Major State Basic Research
Development Program (2006CB806105). Mr. Hanshuo Zhang
did some experimental work. Cheung Kong Scholars Pro-
gramme, Qiu Shi Science & Technologies Foundation, BASF,
and Dow Corning Corporation are gratefully acknowledged.
Supporting Information Available: General experimental
procedures, characterization data for all new starting materials and
1
products except illustrative examples, copies of H and 13C NMR
spectra for all new compounds. This material is available free of
charge via the Internet at http://pubs.acs.org.
JO070160U
J. Org. Chem, Vol. 72, No. 9, 2007 3491