Symmetric Bridgehead-to-Bridgehead Coupling of Bicyclo[1.1.1]pentanes and [n]Staffanes

Article abstract of DOI:10.1021/jo971419j

Symmetrical bridgehead-to-bridgehead coupling of bicyclo[1.1.1] pentane cages has been effected in 48-70% yields by the cuprate oxidation method.

Full text of DOI:10.1021/jo971419j

2116
J . Org. Chem. 1998, 63, 2116-2119
Sym m etr ic Br id geh ea d -to-Br id geh ea d Cou p lin g of
Bicyclo[1.1.1]p en ta n es a n d [n ]Sta ffa n es
Ctibor Mazal,† Alex J . Paraskos,‡ and J osef Michl*,‡
Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, and
Department of Organic Chemistry, Masaryk University, Kotla´rˇska´ 2, CZ-611 37 Brno, Czech Republic
Received J uly 31, 1997
Symmetrical bridgehead-to-bridgehead coupling of bicyclo[1.1.1]pentane cages has been effected
in 48-70% yields by the cuprate oxidation method.
Sch em e 1
In tr od u ction
For some time, we have worked with axially function-
alized [n]staffanes (oligomers of [1.1.1]propellane), which
are of interest for use as rigid rods in a molecular-size
“Tinkertoy”1 construction kit.2,3 So far, the only synthetic
access to these structures is the oligomerization of [1.1.1]-
propellane, followed by separation of rods of different
lengths. Although this was quite adequate initially,
when rods of all lengths were desired, it provides only
poor yields of rods of any particular length, except the
shortest. Clearly, procedures for symmetrical and un-
symmetrical bridgehead-to-bridgehead coupling of shorter
[n]staffanes into longer ones would offer a much better
synthetic route to the longer members of the series.
Presently, we report that the cuprate oxidation proce-
dure4 can be used for symmetrical coupling, permitting
a doubling of rod length.
backside attack. The instability of bridgehead carboca-
tions in the bicyclo[1.1.1]pentane cage7 precludes the use
of methods based on nucleophilic substitution.8
We have chosen the readily accessible2 1-iodo-3-
phenylbicyclo[1.1.1]pentane (1) as a model substrate for
the development of a coupling procedure. In view of the
above, the failure of our initial attempts to couple 1 with
various organometallics, including (3-phenylbicyclo[1.1.1]-
pentyl)zinc chloride, in the presence of nickel(0) or
palladium(0) catalysts was not surprising. We also tried
the radical pathway via a dimethyl boronate that was
followed in certain related reactions,9 but again failed.
On the positive side, the relative stability of bridgehead
carbanions permitted an in situ preparation of bis-
(bicyclo[1.1.1]pentyl)palladium(II) and nickel(II) phos-
phine complexes from (3-phenylbicyclo[1.1.1]pentyl)lithium
(2) and the corresponding dihalides, PdCl2(PPh3)2,
NiBr2[P(n-Bu)3]2, and NiCl2dppp, at low temperature.
The decomposition of these complexes gave 20-40% of
the desired coupling product, 3,3′-diphenyl[2]staffane (3),
in analogy to reductive elimination from other dialkyl-
or diarylpalladium and -nickel complexes10 (Scheme 1).
The success of the reductive coupling on Pd and Ni next
turned our attention to the preparatively more conve-
nient oxidative coupling of dialkyl cuprates.4 We first
tried Lipshutz’s “higher-order” cyanocuprate method
which had been successfully used for preparations of
various biaryls in good or excellent yields,11 and has also
been tested for dialkylcyanocuprates.12 Such a procedure
Resu lts a n d Discu ssion
Only a few examples of coupling involving bond forma-
tion between two tertiary carbon atoms have been
reported so far,5,6 and bridgehead positions appear to be
particularly demanding since the structure prevents a
† Masaryk University.
‡ University of Colorado.
(1) Tinkertoy is a trademark of Playskool, Inc., Pawtucket, RI 02862,
and designates a children’s toy construction set consisting of straight
wooden sticks and other simple elements insertable into spool-like
connectors.
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Robinson, R. E.; McMurdie, N. D.; Kim, T. In Strain and Its Implica-
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ASI Series, Vol. 273; Kluwer Academic Publishers: Dordrecht, The
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Harrod, J . F., Laine, R. M., Eds.; Kluwer: Dordrecht, The Netherlands,
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S0022-3263(97)01419-9 CCC: $15.00 © 1998 American Chemical Society
Published on Web 03/13/1998

Symmetric Coupling of Bicyclopentanes and Staffanes
J . Org. Chem., Vol. 63, No. 7, 1998 2117
Sch em e 2
Sch em e 4
Sch em e 3
Sch em e 5
would offer the possibility of asymmetric coupling. How-
ever, a complex mixture of products was formed when
the lithium derivative 2 was used for the preparation of
the cyanocuprate which was then oxidized by oxygen.
Besides the desired coupling product 3, we detected
1-phenylbicyclo[1.1.1]pentane,13 1-cyano-3-phenylbicyclo-
[1.1.1]pentane,14 and a compound whose spectral proper-
ties suggested the 1-hydroxy-3-phenylbicyclo[1.1.1]pentane
structure. When CuCl2 was used for the cuprate oxida-
tion instead of oxygen, about 50% of the original iodo
derivative 1 was reformed.
Phosphine stabilized cuprates seemed to be a useful
alternative for a symmetric version of the coupling
reaction. Szeimies et al.6 provided an inspiring example
with their synthesis of 1,1′-bi(homocubane). Indeed, 3
was obtained from 1 in 60 ( 10% yield in repeated runs
following a slightly modified protocol, in that a homoge-
neous solution of PPh3 and CuI (2:1) in THF was used in
the cuprate preparation instead of the more hazardous
[CuI‚P(n-Bu)3]4 (Scheme 2).
We next tested the generality of this procedure. The
synthesis of a [4]staffane derivative started with 3,3′-
diiodo[2]staffane (4), easily and specifically accessible by
the insertion of [1.1.1]propellane into a C-I bond of 1,3-
diiodobicyclo[1.1.1]pentane, in which higher staffanes are
not formed.2 Lithiation and silylation of 4 gave 3,3′-bis-
(trimethylsilyl)[2]staffane (5), which was transformed in
about 50% yield to 3-bromo-3′-(trimethylsilyl)[2]staffane
(6) by reaction with NBS and bromine in dichloro-
methane under irradiation. The bromo derivative 6 is
somewhat unstable under the reaction conditions, and
this is most likely responsible for the low yield. No 3,3′-
dibromo[2]staffane was detected. Lithiation of 6 by
t-BuLi in ether at -40 °C followed by oxidative cuprate
coupling at -60 °C gave 3,3′′′-bis(trimethylsilyl)[4]staffane
(7) in 40 ( 10% yield in repeated runs (Scheme 3).
The next test case involved the coupling of 1-(12-(tri-
hexylsilyl)-1,12-dicarba-closo-dodecaboran-1-yl)-3-iodo-
bicyclo[1.1.1]pentane (8) to yield 3,3′-bis(12-(trihexylsilyl)-
1,12-dicarba-closo-dodecaboran-1-yl)[2]staffane (9), a new
type of structure in which the [n]staffane2 and 12-vertex
p-carborane15,16 rod motifs are mixed. In repeated runs,
the yield was 75 ( 10%. The starting 8 was obtained by
the photochemical insertion of [1.1.1]propellane into the
C-I bond of 1-(trihexylsilyl)-12-iodo-1,12-dicarba-closo-
dodecaborane (10), analogous to its insertion into other
C-I bonds, particularly those in 1,3-diiodobicyclo[1.1.1]-
pentane2 and 1,4-diiodocubane17 (Scheme 4).
Finally, 3,3′-bis(chloromethyl)-2,4:2′,4′-bisethano[2]-
staffane (11) was prepared in 70% yield by the oxidative
cuprate coupling of the bridgehead lithium compound
derived from 1-(chloromethyl)-3-iodo-2,4-ethanobicyclo-
[1.1.1]pentane (12), which was isolated as a byproduct
in the synthesis of 2,4-ethano[1.1.1]propellane,18 where
it probably forms as an adduct of chloroiodomethane on
the propellane (Scheme 5).
Con clu sion
We conclude that the oxidation of bridgehead cuprates
represents a suitable procedure for symmetric coupling
of bridgehead bromides and iodides of the bicyclo[1.1.1]-
pentane and [n]staffane series.
(15) Mu¨ller, J .; Basˇe, K.; Magnera, T. F.; Michl, J . J . Am. Chem.
Soc. 1992, 114, 9721.
(16) Yang, X.; J iang, W.; Knobler, C. B.; Hawthorne, M. F. J . Am.
Chem. Soc. 1992, 114, 9719.
(17) Hassenru¨ck, K.; Murthy, G. S.; Lynch, V. M.; Michl, J . J . Org.
Chem. 1990, 55, 1013.
(11) Lipshutz, B. H.; Kayser, F.; Liu, Z.-P. Angew. Chem., Int. Ed.
Engl. 1994, 33, 1842. Lipshutz, B. H. Synlett 1990, 119.
(12) Bertz, S. H.; Gibson, C. P. J . Am. Chem. Soc. 1986, 108, 8286.
(13) Della, E. W.; Pigou, P. E.; Schiesser, C. H.; Taylor, D. K. J .
Org. Chem. 1991, 56, 4659.
(14) Applequist, D. E.; Renken, T. L.; Wheeler, J . W. J . Org. Chem.
1982, 47, 4985.
(18) Belzner, J .; Gareiss, B.; Polborn, K.; Schmid, W.; Semmler, K.;
Szeimies, G. Chem. Ber. 1989, 122, 1509.

2118 J . Org. Chem., Vol. 63, No. 7, 1998
Mazal et al.
2.34, 12.78, 14.09, 22.58, 23.39, 31.32, 33.38, 48.96, 60.86,
68.06, 86.45; 11B NMR δ -13.9 (br); IR (neat) 2956, 2926, 2856,
2605, 1190, 1100 cm-1; EIMS, m/z 492 (41), 407 (21), 341 (47),
257 (22), 173 (18), 43 (100); HRMS calcd for C25B10H54ISi (M
- H) 619.3970, found 619.3982.
Exp er im en ta l Section
Gen er a l Met h od s. 1-Iodo-3-phenylbicyclo[1.1.1]pentane
(1) and 3,3′-diiodo[2]staffane (4) were prepared by literature
methods.2 [1.1.1]Propellane was prepared solvent-free19 and
dissolved in pentane. 1-(Trihexylsilyl)-1,12-dicarba-closo-do-
decaborane (13) was prepared as described for 1-(triethylsilyl)-
1,10-dicarba-closo-decaborane15 and used for further synthesis
without a full characterization (1H NMR δ 0.39 (m, 6 H), 0.84
(t, 9 H), 1.10-1.33 (m, 24 H), 1.30-3.10 (m, 10 H), 2.80 (s,
1H); 13C NMR δ 12.60, 14.09, 22.60, 23.42, 31.36, 33.43,
carborane carbons not observed). All the reactions were
carried out under an argon atmosphere unless specified
otherwise. Melting points were determined on a Mel-TempII
(Laboratory Devices) apparatus with a microscope attachment
and are uncorrected. 1H, 13C, and 11B NMR spectra were
measured on a Varian VXR-300S spectrometer and referred
to TMS and B(OMe)3, respectively. IR spectra were recorded
on a Perkin-Elmer 1600 Series spectrometer. MS spectra were
taken on a VG 7070EQ-HF Hybrid tandem mass spectrometer.
Elemental analyses were performed by Desert Analytics
Laboratory, Tucson, AZ.
1-(Ch lor om eth yl)-3-iod o-2,4-eth a n obicyclo[1.1.1]p en -
ta n e (12) was formed as a byproduct in the synthesis of 2,4-
ethano[1.1.1]propellane, which followed the procedure of Szei-
mies et al.18 It was isolated by a Kugelrohr distillation of the
residue left after propellane distillation. An analytically pure
sample was prepared by extraction with hexanes followed by
Kugelrohr distillation (0.1 Torr, oven temperature 75-100
°C): 1H NMR δ 1.64 (m, 4 H), 2.53 (s, 2 H), 2.85 (s, 2 H), 3.40
(s, 2 H); 13C NMR δ 19.12, 24.81, 41.36, 48.12, 50.21, 69.20;
IR (neat) 2973, 2944, 2866, 1463, 1288, 1262, 1208, 1187, 1138,
944, 862 cm-1; EIMS, m/z 268 (M, 6.5), 254 (3), 233 (M - Cl,
20), 219 (15), 205 (28), 141 (75), 105 (100). Anal. Calcd for
C8H10ICl: C, 35.78; H, 3.75. Found: C, 35.86; H, 3.73.
Gen er a l P r oced u r e for Cou p lin g Rea ction via Cu -
p r a tes. A CuI-PPh3 complex was prepared in situ by stirring
1 equiv of CuI and 2.2 equiv of PPh3 in THF at room
temperature until CuI was fully dissolved (usually for 1.5 h).
The solution was cooled in a dry ice/acetone bath and added
dropwise via cannula to a well-stirred solution of 2 equiv of
the lithium derivative prepared by lithiation of the corre-
sponding iodo derivative with 2 molar excess of t-BuLi at the
same temperature. The amount of t-BuLi should be as exact
as possible to avoid an excessive formation of a tert-butyl cross-
coupled product; appearance of yellowish color of an excess of
t-BuLi helped to control the addition. 1,4-Dinitrobenzene (1
equiv) in THF was slowly added to the reaction mixture 10
min after the addition of t-BuLi was completed. The mixture
turned in brown within minutes and was stirred for an
additional 1 h at -65 °C before it was allowed to warm to room
temperature. It was then diluted with ether, washed with
aqueous NH4Cl, and dried over MgSO4 with 2 equiv of iodine
to oxidize PPh3. The residue left after the evaporation of
solvents was extracted by ether. The extract was further
purified by chromatography or crystallization.
3,3′-Bis(tr im eth ylsilyl)[2]sta ffa n e (5). A solution of 42
(1.860 g, 4.8 mmol) in THF (50 mL) was added dropwise to a
well-stirred solution of t-BuLi (12 mL, 1.7 M in pentane, 20.4
mmol) in THF (20 mL) at -65 °C. The addition was ac-
complished within 20 min. Chlorotrimethylsilane (2.5 mL, 20
mmol) was added to the mixture after 15 min of additional
stirring at -65 °C. Stirring was continued for 1 h at -65 °C.
Then, the mixture was slowly allowed to warm to room
temperature. Washing of the reaction mixture with a satu-
rated solution of NH4Cl (2 × 20 mL), drying over MgSO4, and
evaporation of the solvent gave a crude product that was
chromatographed on an alumina column with hexanes. Pure
5 (1.23 g, 92%) was isolated as a white crystalline solid after
removing the solvent: mp 124 °C; 1H NMR δ -0.12 (s, 18 H),
1.46 (s, 12 H); 13C NMR δ -3.47, 27.83, 46.18, 48.32; IR (KBr)
2958, 2902, 2857, 1243, 1218, 1176, 917, 833, 743 cm-1; CI+MS,
m/z 277 (M - H, 100). Anal. Calcd for C16H30Si2: C, 69.07; H,
10.79. Found: C, 69.10; H, 10.92.
3,3′-Dip h en yl[2]sta ffa n e20 (3). The general procedure for
coupling was followed. The crude product obtained from 12
(174 mg, 0.65 mmol) was chromatographed on a silica gel
column with 2% Et2O in petroleum ether, yielding 61 mg (66%)
of white crystalline 3. An analytical sample was prepared by
crystallization from hexanes: mp 221.5-222.5 °C; 1H NMR δ
1.91 (s, 12 H), 7.16-7.30 (m, 10 H); 13C NMR δ 38.21, 40.70,
51.10, 126.02, 126.26, 128.09, 141.50; IR (neat) 3022, 2965,
2904, 2867, 1444, 1211, 745, 697 cm-1; EIMS, m/z 286 (M, 31),
285 (M - H, 100), 272 (M - CH2, 28), 271 (69), 258 (64), 243
(60), 229 (50), 215 (38). Anal. Calcd for C22H22: C, 92.26; H,
7.74. Found: C, 92.19; H, 7.97.
3,3′′′-Bis(tr im eth ylsilyl)[4]sta ffa n e (7). Lithiation of 6
was accomplished by an addition of t-BuLi (0.45 mL, 1.7 M in
pentane, 0.76 mmol) to a solution of 6 (100 mg, 0.35 mmol) in
ether (10 mL) at -65 °C and by an additional 4 h of stirring
at -40 °C. Then, the solution was cooled to -65 °C and the
general coupling procedure was followed. The reaction was
quenched with 10 mL of a saturated solution of NH4Cl and,
after an addition of CHCl3 (25 mL), washed twice with water
(10 mL). Combined organic extracts were dried over Na2SO4
and evaporated under reduced pressure. The residue was
dissolved in acetone, yielding 7 (35 mg, 48%) as solid flakes
that were filtered off and washed with acetone. Crystallization
from chloroform gave 7 as colorless needles: mp >156 °C subl;
1H NMR δ -0.10 (s, 18 H), 1.33 (s, 12 H), 1.49 (s, 12 H); 13C
NMR δ -3.54, 28.06, 37.97, 38.46, 45.74, 47.33, 48.70; IR (KBr)
2952, 2900, 2861, 1443, 1247, 1209, 1161, 992, 910, 836, 742,
692, 628, 542 cm-1; CI+MS(NH3) m/z 411(M + H, 100). Anal.
Calcd for C26H42Si2: C, 76.02; H, 10.31. Found: C, 75.54; H,
10.95.
3-Br om o-3′-(tr im eth ylsilyl)[2]sta ffa n e (6). Bromine (25
µL, 0.49 mmol) was added to a solution of 5 (135 mg, 0.49
mmol) and N-bromosuccinimide (90 mg, 0.50 mmol) in dry
dichloromethane (30 mL). The solution was stirred under
incandescent irradiation at -20 °C until the starting 5 was
1
fully consumed (monitored by GC or H NMR). Then, solvent
was removed under reduced pressure and the residue was
sublimed at 30-40 °C/0.1 Torr. The sublimate was dissolved
in pentane and filtered. Evaporation of pentane gave 6 (72
mg, 52%) as a crystalline solid: mp 66-68 °C; 1H NMR δ -0.11
(s, 9 H), 1.54 (s, 6 H), 2.03 (s, 6 H); 13C NMR δ -3.50, 28.96,
38.13, 41.64, 43.98, 49.35, 57.34; IR (KBr) 2955, 1384, 1197,
831 cm-1; CI+MS (NH3), m/z 302 (M + NH4+, 45), 287 (M +
H, 87) 285 (100). Anal. Calcd for C13H21SiBr: C, 54.73; H,
7.42. Found: C, 54.77; H, 7.40.
1-(12-(Tr ih exylsilyl)-1,12-d ica r ba -closo-d od eca bor a n -
1-yl)-3-iod obicyclo[1.1.1]p en ta n e (8). Carborane 13 (353
mg, 1.1 mmol) was lithiated by overnight stirring with n-BuLi
(0.6 mL, 2.5 M in pentane, 1.5 mmol) in 30 mL of ether at
room temperature. After the addition of iodine (400 mg, 16
mmol), the mixture was stirred for 30 min. The crude reaction
mixture was washed with 3 × 10 mL of saturated NH4Cl
solution, filtered through a silica gel pad, and concentrated
under reduced pressure. The material obtained (3.54 g, 80%
1
of 10 by GC analysis; H NMR δ 0.37 (m, 6 H), 0.84 (t, 9 H),
1.10-1.33 (m, 24 H), 1.30-3.10 (m, 10 H); 13C NMR δ 12.70,
14.08, 22.59, 23.35, 31.31, 33.36, carborane carbons not
observed) was irradiated in a stirred pentane solution of [1.1.1]-
propellane (60 mL, 2 mol %) by an incandescent lamp for 36
h. A resulting mixture was chromatographed on silica gel by
hexane, and 2.8 g (88%) of pure 8 was obtained as a viscous
oil: 1H NMR δ 0.39 (m, 6 H), 0.86 (t, J ) 6.6 Hz, 9 H), 1.10-
1.33 (m, 24 H), 2.01 (s, 6 H), 1.2-3.1 (m, 10 H); 13C NMR δ
3,3′-Bis(12-(tr ih exylsilyl)-1,12-d ica r ba -closo-d od eca bo-
r a n -1-yl)[2]st a ffa n e (9). Crude ethereal extract from the
(20) Friedli, A. C. Ph.D. Dissertation, University of Texas, Austin,
1992.
(19) Alber, F.; Szeimies, G. Chem. Ber. 1992, 125, 757.

Symmetric Coupling of Bicyclopentanes and Staffanes
J . Org. Chem., Vol. 63, No. 7, 1998 2119
reaction of 2.8 g (4.95 mmol) of 8 was filtered through a silica
mixture was poured into concentrated NH4Cl (10 mL) and
extracted with ether. The ethereal extract was dried over
MgSO4 and filtered. Solvent was removed under reduced
gel pad and crystallized from THF/methanol (1:1), yielding 65%
1
of white crystals of 9: mp 111-112 °C; H NMR δ 0.38-0.48
1
(m, 12 H), 0.85 (t, J ) 6.6 Hz, 18 H), 1.08-1.32 (m, 48 H),
1.23 (s, 12 H), 1.30-3.04 (m, 20 H); 13C NMR δ 12.85, 14.10,
22.61, 23.44, 31.36, 33.43, 33.87, 40.79, 50.40, 51.28, 67.38;
11B NMR δ -13.3, -14.0; IR (KBr) 2956, 2926, 2856, 2605,
1467, 1209, 1100, 771 cm-1; EIMS m/z 984 (M, 3), 624 (33),
408 (100), 342 (64), 320 (57), 239 (52). Anal. Calcd for
pressure. According to H NMR, the resulting mixture con-
tained 3 (50%), 1-phenylbicyclo[1.1.1]pentane13 (14%), 1-cyano-
3-phenylbicyclo[1.1.1]pentane14 (11%), and 25% of an addi-
tional compound that was not fully characterized due to the
small scale of the reaction, but is suspected to be 1-hydroxy-
3-phenylbicyclo[1.1.1]pentane according to its spectra: 1H
NMR δ 2.19 (s, 6H), 2.20-2.43 (bs, 1H), 7.18-7.32 (m, 5H);
EIMS m/z 159 (M - H, 95), 143 (M - OH, 60), 118 (100), 103
(80), 91 (48), 77 (63). When solid CuCl2 (12 mg, 0.09 mmol)
instead of oxygen was used to oxidize the cyanocuprate, a
mixture of 3 (43%) and 1 (57%) was obtained.
C
50H110B20Si2: C, 61.04; H, 11.27. Found: C, 61.13; H, 11.05.
3,3′-Bis(ch lor om eth yl)-2,4:2′,4′-biseth an o[2]staffan e (11).
The crude product obtained from 100 mg (0.37 mmol) of 12
was chromatographed on a silica gel column to give 35 mg
(70%) of crystalline 11; an analytical sample was obtained by
sublimation at 60-80 °C /0.1 Torr: mp 91-92 °C; 1H NMR δ
1.58-1.69 (m, 8 H), 1.79 (s, 4 H), 2.45 (s, 4 H), 3.32 (s, 4 H);
13C NMR δ 25.74, 40.08, 41.36, 41.52, 43.91, 61.41; IR (KBr)
2962, 2867, 1384, 1259, 1221, 701 cm-1; EIMS m/z 247 (M -
Cl, 19), 235 (24), 233 (28), 219 (64), 205 (45), 169 (100), 167
(83), 155 (95). Anal. Calcd for C16H20Cl2: C, 67.85; H, 7.12.
Found: C, 67.92; H, 7.22.
3,3′-Diphenyl[2]staffane has also been obtained from 1 by
Lipshutz higher-order cyanocuprate coupling and by stoichio-
metric reductive coupling of Pd(II) and/or Ni(II) complexes.
Cu CN Cou p lin g.11 Copper cyanide (8 mg, 0.089 mmol) was
placed in a dry three-necked round-bottom flask (50 mL)
equipped with a gas dispersion tube and a rubber septum. The
flask was again gently dried with a heat gun and allowed to
cool to room temperature under argon. THF (10 mL) was
added and the resulting suspension cooled to -65 °C. Lithia-
tion of 1 (50 mg, 0.185 mmol) THF (10 mL) at -65 °C was
effected with t-BuLi (0.22 mL, 1.7 M in pentane, 0.37 mmol).
The solution was transferred through a cannula to the flask
containing the CuCN suspension. The mixture was warmed
to -40 °C and then recooled to -65 °C and stirred at this
temperature for 0.5 h. Oxygen was then passed through the
mixture for 0.5 h at the same temperature and for an
additional 1.5 h at 0 °C. The reaction was quenched with a
solution of methanol and concentrated NaHSO3 (2 mL). The
P d (II) Cou p lin g. A solution of PdCl2(PPh3)2 (63 mg, 0.09
mmol) in THF (10 mL) was slowly added to a dry ice-cooled
stirred solution of 2, prepared by lithiating 1 (50 mg, 0.185
mmol) with t-BuLi (0.22 mL, 1.7 M in pentane, 0.37 mmol) in
THF (10 mL) at -65 °C. The resulting mixture was allowed
to warm slowly to room temperature. Concentrated NH4Cl
(10 mL) was added, and the mixture was extracted by ether.
The extract was dried over MgSO4 and filtered. Solvent was
removed under reduced pressure. 1H NMR of the crude
mixture showed 26% of 3 and 70% of 1-phenylbicyclo[1.1.1]-
pentane.13
Ni(II) Cou p lin g. When the above procedure was repeated
with NiBr2[P(n-Bu)3]2 (56 mg, 0.09 mmol) or NiCl2dppp (50
mg, 0.09 mmol) catalyst instead of PdCl2(PPh3)2, a similar
mixture of products was obtained, containing 38% and 24% of
3, respectively.
Ack n ow led gm en t. This work was supported by the
U.S. National Science Foundation (grants CHE-9505926
and INT-9413469). We are grateful to Mrs. G. Levina
for technical assistance with some of the experiments
and to Dr. A. V. Blokhin for initial experiments on the
synthesis of 3,3′-bis(trimethylsilyl)[2]staffane.
J O971419J