Isolation of a kinetically stabilized 1,3,6-triphosphafulvene

Full text of DOI:10.1002/1521-3773(20000804)39:15<2781::AID-ANIE2781>3.0.CO;2-5

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[8] R. Steck, thesis, Humboldt-Universität, Berlin, 1998.
the trimerization of tert-butylphosphaacetylene (or 3,3-di-
methyl-1-phospha-1-butyne), together with its valence isomer
2;[1] the structure of 1 was established in 1998.[2, 3] Oligome-
rization of tert-butylphosphaacetylene has been utilized for
the construction of various types of five-membered hetero-
cyclic systems containing polycyclic systems.[4] We now report
one of the valence isomers of triphosphabenzene, utilizing the
2,4,6-tri-tert-butylphenyl group (Mes*). 2,4,6-Tris(2,4,6-tri-
tert-butylphenyl)-1,3,6-triphosphafulvene (3) was formed by
the trimerization of lithium phosphanylidene carbenoid 4
(Scheme 1).[5±7]
[9] a) N. Trong Anh, M. Elian, R. Hoffmann, J. Am. Chem. Soc. 1978, 100,
110; b) P. Jutzi, Chem. Rev. 1986, 86, 983, and references therein.
[10] The DFT calculations indicate no fundamental electronic differences
ꢀ
between the complexes trans-[Cl(L)4W EMe] and 4a ± 7a.
[11] The gradient corrected functionals BP86 were used (A. D. Becke,
Phys. Rev. A 1988, 38, 3098; J. P. Perdew, Phys. Rev. B 1986, 33, 8822).
For the W atom and the elements Ge, Cl, and P the pseudo potentials
(W: P. J. Hay, W. R. Wadt, J. Chem. Phys. 1985, 82, 299; Ge, Cl, P: G.
Igel-Mann, H. Stoll, H. Preuss, Mol. Phys. 1988, 65, 1321) and
corresponding valence basis sets were used (W: 441/2111/21 and 441/
2111/111/1; Ge, Cl, P: 31/31/1 and 211/211/11). Together with the
standard basis sets 6-31G(d) (P. C. Hariharan, J. A. Pople, Theor.
Chim. Acta 1973, 28, 213) and 6-311G(2d,p) (R. Krishnan, J. S.
Binkley, R. Seeger, J. A. Pople, J. Chem. Phys. 1980, 72, 650) for the
remaining elements the combinations II and III were obtained
(Table 1). The calculations were performed with Gaussian98 (Gaus-
sian98, RevisionA.7, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E.
Scuseria, M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A.
Montgomery, Jr., R. E. Stratmann, J. C. Burant, S. Dapprich, J. M.
Millam, A. D. Daniels, K. N. Kudin, M. C. Strain, O. Farkas, J. Tomasi,
V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo,
S. Clifford, J. Ochterski, G. A. Petersson, P. Y. Ayala, Q. Cui, K.
Morokuma, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B.
Foresman, J. Cioslowski, J. V. Ortiz, A. G. Baboul, B. B. Stefanov,
G. Lui, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R. L.
Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A.
Nanayakkara, C. Gonzalez, M. Challacombe, P. M. W. Gill, B.
Johnson, W. Chen, M. W. Wong, J. L. Andres, M. Head-Gordon,
E. S. Replogle, J. A. Pople, Gaussian, Inc., Pittsburgh, PA, 1998) and
CDA 2.1 (charge decomposition analysis; S. Dapprich, G. Frenking,
CDA 2.1, Marburg, 1994).
Mes*
Mes*
Mes*
Br
Br
Br
Li
PB
PA
Mes*
–LiBr
tBuLi
P
C
P
C
Mes* PX
5
4
3
Mes*
W(CO)5
[W(CO)5(thf)]
PB
PA
Mes*
Mes* PX
3w
Scheme 1. Preparation of 3 and 3w. Mes* ˆ 2,4,6-tBu3C6H2.
Dibromophosphaethene 5[8] was allowed to react with two
equivalents of tert-butyllithium at À788C to afford the
phosphanylidene carbenoid 4, after which the reaction
mixture warmed gently to 258C. After purification (silica-
packed column chromatography), 3 was obtained as a deep
red solid together with trace amounts of 2-(2,4,6-tri-tert-
butylphenyl)-1-(2,4,6-tri-tert-butylphenylphosphanyl)acety-
lene (6), 1-(2,4,6-tri-tert-butylphenyl)-1-phosphaacetylene
(7),[5±7, 9] and 6,8-di-tert-butyl-4,4-dimethyl-1-phospha-3,4-di-
hydronaphthalene (8).[5, 6, 10] The 31P NMR spectrum of 3
[12] P. Jutzi, J. Organomet. Chem. 1990, 400, 1.
Isolation of a Kinetically Stabilized
1,3,6-Triphosphafulvene**
Shigekazu Ito, Hiroki Sugiyama, and
Masaaki Yoshifuji*
Ph
tBu
Mes*
P
P
Mes*
H
Substitution of some of the sp2-hybridized carbon atoms in
conjugated systems with heavier main-group elements, such as
phosphorus atoms, is of interest but requires kinetic stabiliza-
tion with bulky substituents. In 1995, 2,4,6-tri-tert-butyl-1,3,5-
triphosphabenzene (1) was first reported, prepared through
P
C C Mes*
Mes* C P
tBu
Ph
9
Me Me
6
7
8
tBu
tBu
W(CO)5
P
Mes*
Mch
Se
Mch
P
P
O
P
P
Te
tBu
tBu
tBu
tBu
tBu
P
10
12
11
P
P
P
P
tBu
tBu
P
tBu
2
1
shows an ABX system. The signal of the exocyclic phosphorus
atom PX (dP ˆ 313.8) is positioned downfield compared to
X
ring atoms PA and PB but similar to that found for 9 (d ˆ
321.5),[11] due to the electron-withdrawing effects of the 1,3-
diphosphacyclopentadiene moiety.[12] The chemical shifts of
the ring phosphorus atoms in 3 (dP ˆ 291.3, dP ˆ 264.7) are
[*] Prof. Dr. M. Yoshifuji, Dr. S. Ito, H. Sugiyama
Department of Chemistry
Graduate School of Science
Tohoku University
A
B
Aoba, Sendai 980-8578 (Japan)
Fax : (‡81)22-217-6562
close to those for 1,2,4-selenadiphosphole 10 (Mch ˆ
1-methylcyclohexyl).[13] Their coupling constant, J(PA,PB), is
32Hz, which is also similar to that found for 10;[13] values of
the exocyclic coupling constants are 120 and 44 Hz for
J(PA,PX) and J(PB,PX), respectively. The UV/Vis spectrum of
E-mail: yoshifj@mail.cc.tohoku.ac.jp
[**] This work was supported in part by a Grant-in-Aid for Scientific
Research (No. 09239101) from the Ministry of Education, Science,
Sports and Culture, Japan.
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3 has a maxima lmax at 429 nm (lge ˆ 3.48, in hexanes), which
is at a longer wavelength than that for 9 (lmax ˆ 358 nm).[11]
(1.836 Š),[18] which indicates the delocalized p system. The
C1-P1-C3 and C1-P2-C2 angles are 96.6(3) and 100.2(3)8,
respectively, which are smaller than those found in 11
(101.7(3) and 106.3(3)8).[14]
Compound 3 is regarded as a trimer of the phosphanylidene
carbene. As depicted in Scheme 2, phosphaalkyne 7 is first
generated from 4 through elimination of LiBr, followed by a
Compound
3 was treated with excess amount of
[W(CO)5(thf)] to afford the pentacarbonyltungsten complex
3w as a deep red solid (Scheme 1). An ABX system was also
observed in the 31P NMR spectrum of 3w and the signal for
the PA atom shifted remarkably (dP ˆ 268.4) relative to that
A
found in 3.
Complex 3w was recrystallized from toluene at 08C to
afford a suitable crystal for its structural determination.
Figure 1 shows an ORTEP drawing of the molecular structure
of 3w together with some selected bond lengths and angles,
unambiguously indicating that the metal center coordinates to
Br
C
P
Mes*
7
4
P
7
4
–LiBr
C(Li)Mes*
Br
C
Mes*
P
P C(Li)Mes*
–LiBr
3
P
C
Mes*
Scheme 2. Proposed mechanism for the formation of 3.
[1,2] Fritsch ± Buttenberg ± Wiechell-type migration.[9] The
phosphanylidene carbenoid 4 reacts with two equivalents of
7 in succession and, finally, another LiBr unit was eliminated
upon annelation to 3.[19] The presence of traces of the
phosphanylacetylene 6 could be regarded as a reaction
product arising from a dimerization of 4 with expulsion of
one phosphorus atom.[20]
As reported previously, after the reaction of dibromophos-
phaethene 5 with nBuLi, 3 was not detected but 8 was
obtained as a major product.[10a] Although it is difficult to
rationalize this observation on the basis of reactivity differ-
ences between nBuLi and tBuLi,[21] the aggregation of 4
generated with tBuLi may be dissimilar as that generated with
nBuLi. The formation of ªfreeº phosphaalkyne 7 via a [1,2]
migration would be preferred if tBuLi was employed for the
reaction; on the other hand, the intramolecular cyclization
would become more facile if nBuLi was used. Such effects
were observed in the rearrangement reaction to afford
Figure 1. An ORTEP representation of the molecular structure of 3w with
30% probability ellipsoids. Hydrogen atoms are omitted for clarity.
Selected bond lengths [Š] and angles [8]: W-P2 2.480(2), P1-C1 1.689(7),
P1-C3 1.815(6), P2-C1 1.801(7), P2-C2 1.703(7), P3-C3 1.710(6), C2-C3
1.447(8), C1-Cipso(Mes*) 1.518(9), C2-Cipso(Mes*) 1.525(8), P3-Cipso(Mes*)
1.857(7); W-P2-C1 129.9(2), W-P2-C2 129.9(2), C1-P1-C3 96.6(3), P1-C1-P2
113.7(4), C1-P2-C2 100.2(3), P2-C2-C3 112.8(4), C2-C3-P1 116.8(5), P1-C3-
P3 120.0(3), C2-C3-P3 123.3(5), C3-P3-Cipso(Mes*) 101.7(3).
phosphaalkyne
7 from (E)-2-chloro-1-(2,4,6-tri-tert-butyl-
phenyl)-2-phosphaalkene and various butyllithium spe-
cies.[9a, b]
As stated, 1,3,6-triphosphafulvene 3 is one of the valence
isomers of triphosphabenzenes. Compound 3 is deeply
colored compared to 1, which correspond to the properties
of fulvene versus benzene.[22] Neither the isomerization of 3
nor the trimerization of 7 affording the corresponding
triphosphabenzene derivative has been previously observed.
An ab initio calculation (RHF/3-21G* level)[23, 24] on non-
substituted systems indicated that 1,3,6-triphosphafulvene is
less stable by 20.9 kcalmolÀ1 than 1,3,5-triphosphabenzene.
We postulate that the bulky Mes* groups play an important
role in controlling the framework of the molecule.
the P2(P A) atom. The exocyclic l3s2 phosphorus atom takes a
cis configuration, probably due to the steric congestion. The
triphosphafulvene framework (P1 ± P3,C1 ± C3), W atom, and
three ipso carbon atoms of the Mes* groups are coplanar to
within 0.074(8) Š. This plane lies at angles of 84.58 (P3), 90.08
(C1), and 90.08 (C2) to the mean aromatic rings of the three
À
Mes* groups. The W P2 distance is 2.480(2) Š, while the
À
À
P1 C1 and P2 C2distances (1.689(7) and 1.703(7) Š, re-
ˆ
spectively) are close to the P C lengths of tungsten-com-
plexed
1,2,4-telluradiphosphole
11
(1.695(7)
and
Experimental Section
1.702(7) Š).[14] The P3 C3 distance is 1.710(6) Š, which is
À
ˆ
close to the P C length in p-phosphaquinone 12
3: A solution of 5 (500 mg, 1.12mmol) in THF (40 mL) was treated with
tert-butyllithium (2.25 mmol, 1.50 molLÀ1 in n-pentane) at À788C and
allowed to warm to 258C. The reaction mixture was stirred for 1 h and the
solvent was removed in vacuo. The residue was extracted with n-hexane
and, in the 31P NMR spectrum of the extract, mainly 3 was observed
together with trace amounts of 6,[25] 7, and 8. 3 was isolated by column
chromatography (SiO2, cyclohexane); yield: 57.2mg (18%). 3: Red plates,
m.p. 93 ± 958C (dec.); 1H NMR (200 MHz, CDCl3): d ˆ 7.54 (m, 2H; Harom),
(1.705(2) Š).[15] The C2 C3 distance (1.447(8) Š) is similar
À
À
to the C C length in the 1,4-diphospha-1,3-butadiene sys-
tem.[16] The P1 C3 length (1.815(6) Š) is shorter than the P C
single bond in the straight-chain 1,3-diphospha-1,3-butadiene
À
À
system.[17] Both of the P C single bonds in the triphospha-
À
À
fulvene system are shorter than the average P Csp2 distance
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7.43 (m, 2H; Harom), 7.25 (m, 2H; Harom), 1.45 (s, 18H; o-C(CH3)3), 1.38 (s,
36H; o-C(CH3)3), 1.33 (s, 9H; p-C(CH3)3), 1.28 (s, 9H; p-C(CH3)3), 1.26 (s,
9H; p-C(CH3)3); 31P{1H} NMR (81 MHz, CDCl3): d ˆ 313.8 (PX), 291.3
(PA), 264.7 (PB) (2J(PA,PB) ˆ 32, 2J(PA,PX) ˆ 120, 3J(PB,PX) ˆ 44 Hz); UV/
Vis (hexanes): lmax (lge) ˆ 429 nm (3.48); FAB-MS: m/z (%): 864 (19)
[4] a) K. B. Dillon, F. Mathey, J. F. Nixon, Phosphorus: The Carbon Copy,
Wiley, Chichester, 1998; b) J. F. Nixon, Chem. Soc. Rev. 1995, 319;
c) A. Mack, M. Regitz, Chem. Ber. 1997, 130, 823.
[5] M. Yoshifuji, J. Chem. Soc. Dalton Trans. 1999, 3343, and references
therein.
[6] S. Ito, K. Toyota, M. Yoshifuji, Phosphorus Sulfur Silicon 1999, 147,
441.
[7] E. Niecke, M. Nieger, O. Schmidt, D. Gudat, W. W. Schoeller, J. Am.
Chem. Soc. 1999, 121, 519.
[8] a) R. Appel, C. Casser, M. Immenkeppel, Tetrahedron Lett. 1985, 30,
3551; b) S. J. Goede, F. Bickelhaupt, Chem. Ber. 1991, 124, 2677.
[9] a) M. Yoshifuji, T. Niitsu, N. Inamoto, Chem. Lett. 1988, 1733; b) M.
Yoshifuji, H. Kawanami, Y. Kawai, K. Toyota, M. Yasunami, T. Niitsu,
N. Inamoto, Chem. Lett. 1992, 1053; c) R. Appel, M. Immenkeppel, Z.
Anorg. Allg. Chem. 1987, 553, 7; d) V. D. Romanenko, M. Sanchez,
‡
‡
[M ], 275 (100) [Mes*P À H]. 6: Colorless needles (MeOH), m.p. 173 ±
1748C (dec.); 1H NMR (200 MHz, CDCl3): d ˆ 7.44 (d, 2H, 4J(P,H) ˆ
1
2.5 Hz; Harom, PMes*), 7.25 (s, 2H; Harom, CMes*), 6.13 (d, 1H, J(P,H) ˆ
244.2 Hz; PH), 1.62 (s, 18H; o-C(CH3)3, PMes*), 1.35 (s, 9H; p-C(CH3)3,
PMes*), 1.29 (s, 18H; o-C(CH3)3, CMes*), 1.27 (s, 9H; p-C(CH3)3,
CMes*); 13C{1H}-NMR (151 MHz, CDCl3): d ˆ 155.3 (d, 2J(P,C) ˆ 9.2Hz;
o-Carom, PMes*), 153.2(d, 4J(P,C) ˆ 1.2Hz; o-Carom, CMes*), 150.2(s; p-
1
C
arom, PMes*), 149.6 (s; p-Carom-CMes*), 124.9 (d, J(P,C) ˆ 24.7 Hz; Cipso
,
,
PMes*), 122.3 (d, 3J(P,C) ˆ 4.3 Hz; m-Carom, PMes*), 120.6 (s; m-Carom
CMes*), 117.4 (s, Cipso, CMes*), 105.3 (s; P C C), 98.7 (d, 1J(P,C) ˆ
À ꢀ
À ꢀ
Á
17.3 Hz; P C C), 38.2(s; o-C(CH3)3-PMes*), 36.3 (s; o-C(CH3)3-CMes*),
T. V. Sarina, M.-R. Mazieres, R. Wolf, Tetrahedron Lett. 1992, 33,
35.1 (s; p-C(CH3)3-CMes*), 35.0 (s; p-C(CH3)3, PMes*), 32.6 (d, 4J(P,C) ˆ
7.2Hz; o-C(CH3)3, PMes*), 31.4 (s; p-C(CH3)3-PMes*), 31.2(s; p-C(CH3)3-
CMes*), 30.5 (s; o-C(CH3)3-CMes*); 31P NMR (81 MHz, CDCl3): d ˆ
2981; e) H. Jun, V. G. Young, R. Angelici, Organometallics 1994, 13,
2444.
[10] a) S. Ito, K. Toyota, M. Yoshifuji, Chem. Commun. 1997, 1637; see
also: b) R. A. Aitken, P. N. Clasper, N. J. Wilson, Tetrahedron Lett.
1999, 40, 527l.
À98.6 (d, J(P,H) ˆ 244.2 Hz); IR (KBr): nÄ ˆ 2378, 2148 cmÀ1; MS (70 eV,
1
‡
‡
EI): m/z (%): 546 (69) [M ], 489 (100) [M À tBu]; elemental analysis calcd
for C38H59P: C 83.46, H 10.87; found: C 82.68, H 10.99.
[11] G. Märkl, K. M. Raab, Tetrahedron Lett. 1989, 30, 1077.
[12] a) R. Bartsch, P. B. Hitchcock, J. F. Nixon, J. Chem. Soc. Chem.
Commun. 1987, 1146; b) A. H. Cowley, S. W. Hall, Polyhedron 1989, 8,
849; c) N. Maigrot, L. Ricard, C. Charrier, F. Mathey, Angew. Chem.
1990, 102, 575; Angew. Chem. Int. Ed. Engl. 1990, 29, 534.
[13] S. M. F. Asmus, U. Bergsträûer, M. Regitz, Synthesis 1999, 1642.
[14] M. D. Francis, D. E. Hibbs, P. B. Hitchcock, M. B. Hursthouse, C.
Jones, T. Mackewitz, J. F. Nixon, L. Nyulaszi, M. Regitz, N. Sakarya, J.
Organomet. Chem. 1999, 580, 156.
[15] S. Sasaki, F. Murakami, M. Yoshifuji, Angew. Chem. 1999, 111, 351;
Angew. Chem. Int. Ed. 1999, 38, 340.
[16] a) S. Ito, K. Toyota, M. Yoshifuji, Chem. Lett. 1995, 747; b) S. Ito, M.
Yoshifuji, Chem. Lett. 1998, 651; c) M. Yoshifuji, N. Yamada, A.
Maack, K. Toyota, Tetrahedron Lett. 1998, 39, 9481; d) W. W.
Schoeller, U. Tubbesing, Chem. Ber. 1996, 129, 419.
[17] a) R. Appel, P. Fölling, W. Schuhn, F. Knoch, Tetrahedron Lett. 1986,
27, 1661; b) S. M. Bachrach, M. Liu, J. Org. Chem. 1992, 57, 2040.
[18] F. H. Allen, O. Kennard, D. G. Watson, J. Chem. Soc. Perkin Trans.
1987, S1.
[19] Taking this reaction mechanism into account, we hoped to obtain 3 in
a better yield by a direct treatment of 4 with 7. Thus, we examined the
reaction of 4, prepared from 5 and tBuLi, with 7. In fact, 1,3,6-
triphosphafulvene 3 was observed in the reaction mixture (31P NMR)
and could be was isolated by column chromatography (silica gel) with
a little improvement of the yield (20%).
[20] We have previously demonstrated the additions of halocarbenes to
phosphaalkyne 7 affords haloacetylenes which involves an elimination
step of a phosphorus atom: M. Yoshifuji, Y. Kawai, M. Yasunami,
Tetrahedron Lett. 1990, 31, 6891.
[21] A.-M. Sapse, P. von R. Schleyer, Lithium Chemistry: A Theoretical
and Experimental Overview, Wiley, New York, 1995.
3w: A solution of 3 (30.7 mg, 35.5 mmol) in THF (5 mL) was treated with
[W(CO)5(thf)] (about 0.143 mmol, prepared in situ by irradiation of a THF
solution of [W(CO)6] for 8 h with a medium-pressure Hg lamp). The
reaction mixture was stirred for 12h and the solvent was removed in vacuo.
The residue was treated with column chromatography (SiO2, n-hexane)
affording 3w as deep red crystals. Yield 5.5 mg (13%); m.p. 176 ± 1798C
1
(dec.); H NMR (200 MHz, CDCl3): d ˆ 7.54 (m, 2H; Harom), 7.43 (m, 2H;
Harom), 7.25 (m, 2H; Harom) 1.45 (s, 18H; o-C(CH3)3), 1.37 (s, 36H; o-
C(CH3)3), 1.33 (s, 9H; p-C(CH3)3), 1.28 (s, 9H; p-C(CH3)3), 1.26 (s, 9H; p-
C(CH3)3); 31P{1H} NMR (81 MHz, CDCl3): d ˆ 318.7 (PX), 268.4 (PA), 260.4
(PB) (J(PA,PB) ˆ 54, J(PA,PX) ˆ 140, J(PB,PX) ˆ 71, J(PA,W) ˆ 277 Hz); IR
‡
(KBr): nÄ ˆ 2071, 1944 cmÀ1; FAB-MS: m/z (%): 1188 (2) [M ‡ H], 864 (13)
‡
‡
[M À W(CO)5], 545 (100) [Mes*2C2P ].
Crystal data for 3w (C62H87O5P3W): Mr ˆ 1189.14, deep red prisms
crystallized from toluene at 08C, dimensions 0.30 Â 0.20 Â 0.20 mm3,
monoclinic, space group P21/n (no. 14), a ˆ 10.776(5), b ˆ 20.961(2), c ˆ
28.372(5) Š, b ˆ 91.43(3)8, Vˆ 6406(3) Š3, Z ˆ 4, 1calcd ˆ 1.233 gcmÀ3
,
F(000) ˆ 2472.00, m ˆ 1.923 mmÀ1
,
Tˆ 298(1) K.
A Rigaku RAXIS-IV
imaging plate detector with graphite-monochromated MoKa radiation
(l ˆ 0.71070 Š) was used. Of 9153 reflections measured (2qmax ˆ 50.08),
6240 were observed (I > 3.0s(I)). The structure was solved by direct
methods (SIR92),[26] expanded using Fourier techniques (DIRDIF94),[27]
and refined by full-matrix least squares on F for 628 variable parameters.
The non-hydrogen atoms, except the disordered C atoms, were refined
anisotropically. The disordered C atoms of the methyl groups at the p-
position of the C1-bonded Mes* group were refined isotropically. Hydro-
gen atoms were included but not refined. R ˆ 0.049 for I > 3.0s(I) and Rw ˆ
0.110 for all data. Goodness of fit S ˆ 1.30 for all observed reflections.
Max./min. electron density ˆ 0.77/ À 0.73 eŠÀ3. Structure solution, refine-
ment, and graphical representation were carried out using the teXsan
package.[28] Crystallographic 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-
140669. Copies of the data can be obtained free of charge on application to
CCDC, 12Union Road, Cambridge CB21EZ, UK (fax: ( ‡44)1223-336-
033; e-mail: deposit@ccdc.cam.ac.uk).
[22] J. H. Day, Chem. Rev. 1953, 53, 167.
[23] J. S. Binkley, J. A. Pople, W. J. Hehre, J. Am. Chem. Soc. 1980, 102, 939.
[24] An ab initio calculation was performed using a PC-SPARTAN
program package available from Wavefunction, Inc (Irvine, CA).
[25] A separate reaction of
5 (143 mg, 0.319 mmol) with tBuLi
(0.630 mmol) in THF (12mL) under similar conditions afforded
6
(12% yield) together with 8 (2% yield), 3, and 7 (trace amounts, only
observed in 31P NMR spectra).
Received: February 22, 2000 [Z14754]
[26] A. Altomare, M. C. Burla, M. Camalli, M. Cascarano, C. Giacovazzo,
A. Guagliardi, G. Polidori, J. Appl. Crystallogr. 1994, 27, 435.
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