Synthesis of selectively deuterated fulvenes and indenes from enediynes

Article abstract of DOI:10.1039/b417493n

The method for producing selectively deuterated fulvenes and indenes from enediynes was described. Fulvenes and benzofulvenes were used as a key intermediates in the total synthesis of several natural products. Subsequent destannylation were achieved usin

Full text of DOI:10.1039/b417493n

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C O M M U N I C A T I O N
Synthesis of selectively deuterated fulvenes and indenes from
enediynes†
Scott W. Peabody, Boris Breiner, Serguei V. Kovalenko, Satish Patil and Igor V. Alabugin*
Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida,
32306-4390, USA. E-mail: alabugin@chem.fsu.edu; Fax: +1 850 644 8281;
Tel: +1 850 644 5795
Received 2nd September 2004, Accepted 16th November 2004
First published as an Advance Article on the web 14th December 2004
A facile enediyne→fulvene→indene transformation pro-
vides a route to all possible isotopomers of substituted
fulvenes and indenes.
Results and discussion
In this approach, the fulvene moiety is assembled through a 5-
exo-dig radical cyclization initiated by Bu3Sn radical addition
to diaryl enediynes11 (Scheme 1) – the first synthetically useful
application of reaction of an enediyne moiety with radical
reagents, a process which has been only briefly studied so
far.12,13,14 This process lends itself to the preparation of selectively
deuterated fulvene isotopomers because the whole sequence
introduces two hydrogen atoms into the fulvene moiety in
two mechanistically separate and synthetically orthogonal steps
(Scheme 2). In the first stage, either H or D is introduced
at the exocyclic double bond depending on the choice of the
tin reagent (Bu3SnH or Bu3SnD). Subsequent destannylation
can be achieved using a source of either protons or deuterons
(HCl or DCl), thus introducing either H or D at the endocyclic
benzofulvene position.
Introduction
Interest in substituted fulvenes and benzofulvenes stems from
their potential as building blocks for the preparation of met-
allocene catalysts,1 and from the application of fulvenes as
electron acceptors in material science and molecular electronics.2
Fulvenes and benzofulvenes have also been used as key inter-
mediates in the total synthesis of several natural products and
patented as anti-inflammatory agents having antipyretic and
analgesic activity.3 Deuterated indenes have received significant
attention as mechanistic probes, e.g., in Clemmensen reduction,4
photochemistry of alkylindenes,5 hydrogenolysis,6 ruthenium-
mediated cycloaromatization,7 etc.8
Recently, we discovered a photochemical transformation of
enediynes to indenes,9 which is accompanied by four formal
hydrogen abstractions from the environment. In order to
determine whether these hydrogens are transferred as H-atoms
or protons, an important aspect in understanding the DNA-
cleaving properties of these molecules, we carried out this
reaction in the presence of CH3OD and found that it results
in a mixture of indene isotopomers, with varying extent of D
incorporation at both of the methylene positions (Scheme 1).
In order to understand the details of D-incorporation in the
individual steps of the enediynes–indene cascade, we needed to
prepare the fulvene and indene isotopomers. Since they were
not available through literature routes,10 we developed a new
approach to selectively deuterated fulvenes and indenes, which
we report in this paper.
Scheme 2 Synthesis of the four fulvene isotopomers, R = TFP, Ph.
D-incorporation at the endocyclic position through hydrolytic
deuteriodestannylation proceeds with excellent efficiency (see
the Supporting Information for the details†). On the other hand,
reaction of bis-TFP substituted enediyne 1 with Bu3SnD in
toluene, which is the most common solvent for such processes,
† Electronic supplementary information (ESI) available: experimental
procedures, 1H and 13C spectra for compounds 1, 3–6 and 8–14. See
http://www.rsc.org/suppdata/ob/b4/b417493n/
Scheme 1 Photochemical reactions leading to indene isotopomers (top) and tin-promoted radical cyclization leading to fulvene (bottom); TFP =
tetrafluoropyridine.
2 1 8
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 8 – 2 2 1
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
©

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resulted in only ∼50% D-incorporation at the exocyclic double
bond for the (E)-isomer, and ∼56% D-incorporation for the
(Z)-isomer. At a higher Bu3SnD concentration,15 deuterium
incorporation increases (∼69% for the (Z)-isomer, 66% for the
(E)-isomer) but still remains incomplete. These results point to
H-atom abstraction from the benzylic position of toluene solvent
as a competing process (commercial Bu3SnD is 96% deuterated).
Despite the much higher concentration of toluene compared
to the tin reagent ([PhCH3] ∼9 M, [Bu3SnD] ∼3 × 10−4 M)
and the contribution from the primary H/D isotope effect,
this observation may seem surprising, taking into consideration
the dramatic differences in the X–H bond dissociation energies
for Bu3SnH (74 kcal mol−1)16 and toluene (88 kcal mol−1).17
However, when the difference in reaction energies is translated
into the H-abstraction barriers using Marcus theory,18 one
would expect H-abstraction from toluene to proceed only
∼105 times more slowly. A possible explanation for the small
but consistent difference in the extent of deuteration between the
(E)- and (Z)-isomers involves a weak non-covalent interaction
between toluene and the electron-deficient TFP moiety leading
to precoordination of toluene next to the radical center. This
interaction may be more important in formation of the (E)-
isomer where the toluene molecule can be associated with both
TFP moieties. Such interactions should also contribute to the
considerable degree of H-atom abstraction from the solvent –
a hypothesis which is consistent with the higher amount of D-
incorporation (∼75%) in the case of R = phenyl even at lower
Bu3SnH concentrations.
cyclic double bond to form a substituted cyclopentadienyl anion.
The cyclopentadienyl anion can then be trapped selectively using
either H2O or D2O to form selectively deuterated indenes 10–13
(Scheme 4).19 In principle, trapping by other electrophiles, e.g.,
ferrous chloride, to directly form a metallocene complex20 or by
Me3SiCl11 should also be possible.
Scheme 4 Reactions of LiAlH4 (LiAlD4) with fulvene.
Conclusion
The enediyne→fulvene→indene sequence provides a choice for
selective introduction of hydrogen isotopes through a radical,
electrophilic, or nucleophilic form at either of two positions
of an indene or a fulvene moiety. Applications of this method
for mechanistic studies of photochemical enediyne→indene
transformations and of metallocene catalysis will be reported
in due course.
The efficiency of deuteration can be dramatically increased by
using a solvent incapable of hydrogen atom donation. We found
that in benzene or a,a,a-trifluorotoluene, the observed amount of
H-incorporation can be explained by the 4% of residual Bu3SnH
in Bu3SnD.
The fulvene isotopomers can be further transformed to a
variety of indenes with the selective introduction of either
protium or deuterium. Nucleophilic attack at the exocyclic
double bond by an organolithium compound leads to formation
of the cyclopentadienyl anion lithium salt. Subsequent addition
of either a proton or deuteron to the cyclopentadienyl moiety
during workup with either H2O or D2O provides substituted
indenes 7–9 (Scheme 3). This procedure combined with the
appropriate deuterated fulvene provides a synthetic route to any
of the possible indenes illustrated in Scheme 3. Although the
initial radical cyclization results in a mixture of (E/Z)-isomers,
their subsequent transformation to indene converges to a single
isomer.
Experimental
General
NMR spectra were recorded on a Varian Gemini 300 MHz
spectrometer at 300 MHz (1H NMR) and 75.4 MHz (13C
NMR), respectively, in CDCl3 unless otherwise noted. 19F NMR
was performed on a Bruker 300 MHz spectrometer. Mass
spectra were measured on a Jeol JMS-600H. GC analyses were
conducted on a Varian CP-3800 GC. 1,2-Diiodobenzene was
synthesized according to the reported method.21 The synthetic
procedures for 1 and compounds derived from it are given below.
For synthesis of remaining compounds, as well as spectral data,
please refer to the Supporting Information.†
The reaction of LiAlH4 or LiAlD4 proceeds in a similar fash-
ion with the nucleophile (hydride or deuteride) attacking the exo-
1,2-Bis(phenylethynyl)benzene (1)
A mixture of 1,2-diiodobenzene (3.00 g, 9.09 mmol), bis(tri-
phenylphosphine)palladium(II) dichloride (0.7 g, 1.00 mmol),
and copper(I) iodide (0.39 g, 2.02 mmol) in Et3N (75 ml) was de-
gassed by the freeze–pump–thaw method. The solution was
brought to reflux and phenylacetylene (2.05 g, 20.0 mmol) was
added. The reaction mixture was allowed to reflux overnight.
The reaction mixture was filtered through Celite, washed with
saturated ammonium chloride solution, water, and dried over
MgSO4. Column chromatography (silica gel, hexanes) provided
1.95 g (77%) of 1 as an off-white solid, mp 51–52 ◦C (lit.10 51–
◦
1
52 C); H NMR: d 7.57 (m, 6H), 7.32 (m, 8H); 13C NMR: d
131.8, 131.6, 128.4, 128.3, 128.0, 125.8, 123.3; 93.6, 88.3; HRMS
(EI, 70 eV) calcd. for C22H14 (M+) 278.10955, found 278.10944.
2-Phenyl-1-(phenylmethylene)-1H-indene (3)
A solution of diyne 1 (94 mg, 0.336 mmol) in anhydrous toluene
(5 ml) was brought to reflux in a dry three-neck flask. A
solution of tributyltin hydride (120 mg, 0.412 mmol) and AIBN
(6 mg, 0.037 mmol) in anhydrous toluene (5 ml) was added by
Scheme 3 Synthesis of substituted indene isotopomers.
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 8 – 2 2 1
2 1 9

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syringe pump over 1 h and the reaction mixture was allowed
to reflux for 2 h. The toluene was evaporated in vacuo and the
reaction mixture was redissolved in dichloromethane (5 ml).
Concentrated HCl (5 ml) was added and the reaction was stirred
vigorously for 1 h. The organic layer was washed with water,
and dried over MgSO4. Flash chromatography (40 g silica gel,
hexanes) afforded 77 mg (82%) of (E/Z)-3 as a yellow oil. NMR
and GC data provided a 6 : 1 E : Z ratio. 10 mg of pure (E)-isomer
was isolated in the first few fractions of the separation. 1H NMR:
d 7.47 (m, 11H), 7.32 (s, 1H), 7.29 (m, 1H), 7.22 (td, J = 7.4 Hz,
J = 0.9 Hz, 1H), 6.96 (td, J = 7.5 Hz, J = 1.3 Hz, 1H), 6.88
(s, 1H); 13C NMR: d 144.3, 143.2, 140.3, 136.8, 136.0, 134.7,
134.7, 129.6, 129.6, 129.3, 128.4, 128.3, 128.2, 128.2, 127.4,
124.9, 123.3, 120.7; pure (Z)-isomer was isolated by preparative
7.57 (m, 1H), 7.48 (m, 6H), 7.38 (m, 4H), 7.30 (m, 1H), 7.25.
(m, 2H), 4.48 (t, J = 7.9, 14H), 3.95 (br s, 0.5H), 3.77 (br s,
0.5H), 2.30 (m, 2H), 1.29 (m, 4H), 0.88 (m, 3H); 13C NMR:
d 144.8, 143.7, 143.5, 143.2, 140.4, 138.0, 128.4, 128.3, 128.3,
129.0, 127.6, 127.0, 125.9, 125.9, 124.2, 123.5, 122.0, 42.1, 42.0
(t, J = 19.3 Hz), 32.2, 30.3, 22.6, 13.9; HRMS (EI, 70 eV) calcd.
for C26H25D (M+) 339.20973, found 339.20917.
(3,3-Dideutero-2-phenylindenyl)deutero(fluorenyl)phenylmethane
(9)
A solution of 1 (200 mg, 0.719 mmol) in anhydrous toluene
(10 ml) was brought to reflux in a dry three-neck flask. A solution
of tributyltin deuteride (251 mg, 0.863 mmol) and AIBN (6 mg,
0.037 mmol) in anhydrous toluene was added by syringe pump
over 1 h and the reaction mixture was allowed to reflux for 2 h.
The toluene was evaporated in vacuo and the reaction mixture
was dissolved in dichloromethane (5 ml). 20% DCl in D2O (5 ml)
was added and the reaction was stirred vigorously for 1 h.
The organic layer was washed with water and extracted with
dichloromethane. The combined organic layer was dried over
magnesium sulfate and concentrated to a residue that was dried
by dissolving in anhydrous toluene and evaporating the solvent
in vacuo. The residue was flushed with argon and dissolved in
THF (3 ml). n-BuLi (1.03 ml of a 1.6 M solution in hexane,
1.0 mmol) was added dropwise to a solution of fluorene (275 mg,
1.65 mmol) in THF (5 ml) at −78 ◦C and slowly brought to
1
thin layer chromatography. H NMR: d 7.77 (s, 1H), 7.70 (m,
1H), 7.31 (m, 2H), 7.22 (m 3H), 7.01 (m, 13H); HRMS (EI,
70 eV) calcd. for C22H16 (M+) 280.12520, found 280.12520.
2-Phenyl-1-(phenylmethylene)-3-deutero-1H-indene (4)
Synthesized analogously to 3, using DCl instead of HCl and
1
yielding 73 mg (75%) of (E/Z)-4 as a yellow oil. H NMR: d
7.47 (m, 11H), 7.32, (s, 1H), 7.29 (m, 1H), 7.22 (td, J = 7.4 Hz,
J = 0.9 Hz, 1H), 6.96 (td, J = 7.5 Hz, J = 1.3 Hz, 1H), 6.88 (s,
0.08H); 13C NMR: d 144.3, 143.2, 140.3, 136.8, 136.0, 134.7,
134.7, 129.6, 129.6, 129.3, 128.4, 128.3, 128.2, 128.2, 127.4,
124.9, 123.3, 120.7; HRMS (EI, 70 eV) calcd. for C22H15D (M+)
281.13148, found 281.13244.
◦
−30 C over 2 h while stirring. The enediyne reaction mixture
was added dropwise and the solution was brought to 0 ◦C over
2 h while stirring. D2O (5 ml) was added, the reaction mixture
was brought to room temperature, and the product was extracted
with diethyl ether. The combined organic layers were dried over
MgSO4 and concentrated to a residue that was purified by
column chromatography (silica gel, 20 : 1 hexane–chloroform)
and recrystallized from a mixture of ethano◦l and water to afford
209 mg (65%) of 9 as white crystals, mp 94 C. 1H NMR: d 7.93
(d, J = 7.6 Hz, 1H), 7.74 (d, J = 7.6 Hz, 1H), 7.70 (d, J =
7.6 Hz, 1H), 7.48 (d, J = 7.2 Hz, 1H), 7.41 (m, 2H), 7.27 (m,
8H), 7.12 (m, 3H), 7.00 (t, J = 7.4 Hz, 1H), 6.90 (m, 2H), 6.69
(m, 2H), 7.62 (d, J = 7.6 Hz, 1H), 5.22 (br s, 1H), 4.17 (d, J =
11.4 Hz, 0.32H), 3.66 (br s, 0.08H), 3.55 (br s, 0.08H); 13C NMR:
d 146.2, 145.7, 145.0, 144.2, 144.2, 143.1, 142.0, 142.0, 141.1,
140.9, 140.7, 140.7, 137.7, 129.3, 128.4, 128.2, 128.1, 127.2,
127.0, 126.8, 126.6, 126.5, 126.3, 126.1, 126.1, 126.0, 124.4,
123.9, 122.5, 119.5, 49.1, 48.1; HRMS (EI, 70 eV) calcd. for
C35H23D3 (M+) 449.22383, found 449.22380.
2-Phenyl-1-(phenyldeuteromethylene)-1H-indene (5)
Synthesized analogously to 3, using tributyltin deuteride instead
of tributyltin hydride and yielding 69 mg (69%) of (E/Z)-5 as a
yellow oil. 1H NMR: d 7.47 (m, 11H), 7.32, (s, 0.14H), 7.29 (m,
1H), 7.22 (td, J = 7.4 Hz, J = 0.9 Hz, 1H), 6.96 (td, J = 7.5 Hz,
J = 1.3 Hz, 1H), 6.88 (s, 1H); 13C NMR: d 144.3, 143.2, 140.3,
136.8, 136.0, 134.7, 134.7, 129.6, 129.6, 129.3, 128.4, 128.3,
128.2, 128.2, 127.4, 124.9, 123.3, 120.7; HRMS (EI, 70 eV) calcd.
for C22H15D (M+) 281.13148, found 281.13237.
2-Phenyl-3-deutero-1-(phenyldeuteromethylene)-1H-indene (6)
Synthesized analogously to 3, using DCl instead of HCl,
tributyltin deuteride instead of tributyltin hydride, and yielding
1
65 mg (65%) of (E/Z)-6 as a yellow oil. H NMR: d 7.47 (m,
11H), 7.32, (s, 0.15H), 7.29 (m, 1H), 7.22 (td, J = 7.4 Hz, J =
0.9 Hz, 1H), 6.96 (td, J = 7.5 Hz, J = 1.3 Hz, 1H), 6.88 (s,
0.05H); 13C NMR: d 144.3, 143.2, 140.3, 136.8, 136.0, 134.7,
134.7, 129.6, 129.6, 129.3, 128.4, 128.3, 128.2, 128.2, 127.4,
124.9, 123.3, 120.7; HRMS (EI, 70 eV) calcd. for C22H14D2 (M+)
282.13775, found 282.13836.
1-Benzyl-2-phenyl-1H-indene (10)
A solution of 3 (80 mg, 0.285 mmol) in THF (10 ml) was
cooled to −30 ◦C. LiAlH4 (16 mg, 0.421 mmol) was added
and the mixture was warmed to room temperature over 2 h. The
reaction mixture was cooled to 0 ◦C and H2O (5 ml) was added
dropwise. The product was extracted with dichloromethane and
the combined organic layers were dried over sodium sulfate
and concentrated to a residue that was purified by column
chromatography (silica gel, hexanes) to afford 55 mg (68%) of
1-(5-Phenylpentyl)-2-phenylindene (7)
n-BuLi (277 mg of a 1.6 M solution in hexane, 1.0 mmol) was
added dropwise to a solution of 3 (280 mg, 1.0 mmol) in THF
(5 ml) at −30 ◦C. The reaction mixture was warmed to room
temperature and stirred for 2 h. Saturated aqueous ammonium
chloride solution (5 ml) was added and the product was extracted
with diethyl ether. The combined organic layer was dried over
MgSO4 and concentrated to a residue that was purified by
column chromatography (silica gel, 20 : 1 hexane–chloroform),
affording 251 mg (74%) of 7 as ayellow oil. 1H NMR: d 7.25 (m,
14 H), 4.28 (t, J = 7.8 Hz, 1H), 3.97 (d, J = 22.5 Hz, 1H), 2.17
(m, 2H), 1.11 (m, 6H), 0.90 (m, 3H); 13C NMR: d 144.9, 144.7,
143.7, 143.5, 143.2, 140.3, 137.9, 129.6, 129.5, 129.0, 128.9,
128.7, 128.4, 128.3, 127.6, 127.0, 125.8, 124.2, 123.4, 121.9, 42.3,
42.1, 42.0, 32.1, 30.2, 22.6, 13.9; HRMS (EI, 70 eV) calcd. for
C26H26 (M+) 338.2035, found 338.2049.
1
10 as an opaque white oil. H NMR: d 7.50 (m, 1H), 7.45 (m,
2H), 7.37 (m, 2H), 7.22 (m, 9H), 4.14 (s, 2H), 3.87 (s, 2H); 13
C
NMR: d 146.5, 142.8, 142.5, 139.5, 137.1, 136.6, 128.5, 128.5,
128.2, 128.0, 127.1, 126.4, 126.0, 124.7, 123.4, 120.2, 41.3 (t,
J = 20.6 Hz) 32.4; HRMS (EI, 70 eV) calcd. for C22H18 (M+)
282.14085, found 282.14269.
1-Benzyl-2-phenyl-1H-indene (11)
Synthesized analogously to 10, using D2O instead of H2O and
yielding 53 mg (66%) of 11 as an opaque white oil. 1H NMR: d
7.50 (m, 1H), 7.45 (m, 2H), 7.37 (m, 2H), 7.22 (m, 9H), 4.15 (s,
2H), 3.87 (m, 1H); 13C NMR: d 146.5, 142.8, 142.5, 139.5, 137.1,
136.6, 128.5, 128.5, 128.2, 128.0, 127.1, 126.4, 126.0, 124.7,
1-(5-Phenylpentyl)-3-deutero-2-phenylindene (8)
Synthesized analogously to 7, using DCl instead of HCl and
yielding 181 mg (74%, yield) of 8 as a yellow oil. H NMR: d
1
2 2 0
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 8 – 2 2 1

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123.4, 120.2, 41.3 (t, J = 20.6 Hz) 32.4; HRMS (EI, 70 eV)
6 V. Ranade and R. Prins, Chem. Eur. J., 2000, 6, 313.
7 J. O’Connor, S. Friese and M. Tichenor, J. Am. Chem. Soc., 2002,
124, 3506.
calcd. for C22H17D (M+) 283.14713, found 283.14597.
8 (a) Cycloalkene–cycloalkene transformations via platina(IV) cyclobu-
tane derivatives: B. Williams and P. Jennings, Inorg. Chim. Acta, 1997,
265, 23; (b) sigmatropic rearrangements: A. Padwa, S. Goldstein, R.
Loza and M. Pulwer, J. Org. Chem., 1981, 46, 1858; (c) dioxygenase-
catalysed hydroxylation: D. Boyd, N. Sharma, N. Bowers, R. Boyle, J.
Harrison, K. Lee, T. Bugg and D. Gibson, Org. Biomol. Chem., 2003,
1, 1298; (d) rearrangements:E. Friedrich and D. Taggart, J. Org.
Chem., 1975, 40, 720; (e) addition of thiols: H. Szmant and J. Baeza,
J. Org. Chem., 1980, 45, 4902.
1-Benzyl-2-phenyl-1H-indene (12)
Synthesized analogously to 10, using LiAlD4 instead of LiAlH4,
D2O instead of H2O, and yielding 52 mg (64%) of 12 as an
1
1
opaque white oil. H NMR (300 MHz, CDCl3) d H NMR: d
7.50 (m, 1H), 7.45 (m, 2H), 7.37 (m, 2H), 7.22 (m, 9H), 4.12 (m,
1H), 3.87 (s, 2H); 13C NMR: d 146.5, 142.8, 142.6, 139.4, 137.1,
136.5, 128.5, 128.5, 128.3, 128.0, 127.1, 126.4, 126.0, 124.7,
123.4, 120.2, 41.4, 31.8 (t, J = 19.1 Hz); HRMS (EI, 70 eV)
calcd. for C22H17D (M+) 283.14713, found 283.14597.
9 (a) I. V. Alabugin and S. V. Kovalenko, J. Am. Chem. Soc., 2002, 124,
9052; (b) theoretical study: I. V. Alabugin and M. Manoharan, J. Am.
Chem. Soc., 2003, 125, 4495.
10 H. W. Whitlock, P. E. Sandvick, L. E. Overman and P. B. Reichard,
J. Org. Chem., 1969, 34, 879.
1-Benzyl-2-phenyl-1H-indene (13)
11 S. V. Kovalenko, S. Peabody, M. Manoharan, R. S. Clark and I. V.
Alabugin, Org. Lett., 2004, 6, 2457.
12 B. Ko¨nig, W. Pitsch, M. Klein, R. Vasold, M. Prall and P. Schreiner,
J. Org. Chem., 2001, 66, 1742.
13 J. Johnson, D. Bringley, E. Wilson, K. Lewis, L. Beck and A. Matzger,
J. Am. Chem. Soc., 2003, 125, 14708.
14 J. Scott, S. Parkin and J. Anthony, Synlett, 2004, 1, 161.
15 A solution of Bu3SnD was added to a solution of other reagents
using a syringe pump to minimize the formation of acyclic addition
products. “Low concentration” refers to a total toluene volume of
33 ml, while “high concentration” refers to 3 ml of toluene. The
H/D ratios from 1H NMR and high-resolution MS are in perfect
agreement with each other. See Supplementary Information† for
details.
Synthesized analogously to 10, using LiAlD4 instead of LiAlH4,
and yielding 54 mg (67%) of 13 as an opaque white oil. H
1
NMR: d 7.50 (m, 1H), 7.45 (m, 1H), 7.37 (m, 1H), 7.22 (m,
9H), 4.12 (m, 1H), 3.86 (m, 0.5H); 13C NMR: d 146.6, 142.8,
142.5, 139.4, 137.1, 136.5, 128.5, 128.5, 128.3, 128.0, 127.1,
126.4, 126.1, 124.7, 123.4, 120.2, 41.1 (t, J = 19.8), 31.8 (t, J =
19.1); HRMS (EI, 70 eV) calcd. for C22H16D2 (M+) 284.15340,
found 284.15255.
Acknowledgements
The authors are grateful to the National Science Foundation
(CHE-0316598), and the Center for Materials Research and
Technology at Florida State University (MARTECH) for partial
support of this research, and to the 3M Company for an
Untenured Faculty Award (to I. A.).
16 T. J. Burkey, M. Majewski and D. Griller, Adv. Free Radical Chem.
(Greenwich, Conn.), 1990, 1, 159.
17 D. D. M. Wagner and D. Griller, J. Am. Chem. Soc., 1986, 108, 2218.
18 (a) For the interconnection of reaction and activation energies in
hydrogen transfer reactions, see: J. P. Roth, J. C. Yoder, T.-J. Won
and J. M. Mayer, Science, 2002, 294, 2524; (b) I. V. Alabugin, M.
Manoharan, B. Breiner and F. Lewis, J. Am. Chem. Soc., 2003, 125,
9329; (c) for the seminal theoretical treatment, see: R. A. Marcus,
J. Phys. Chem., 1968, 72, 891.
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19 From a practical point of view, it is important to work up the reaction
mixtures expediently since prolonged exposure to base leads to facile
hydrogen exchange at the endocyclic methylene group. This exchange
is especially fast in bis-TFP indenes where it can be used for selective
D-labeling at this position.
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O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 8 – 2 2 1
2 2 1