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ansa-Metallocenes of Calcium and Strontium One-Pot Synthesis of Organometallic Complexes of the Heavier Alkaline Earth Metals.

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E t 2 0 (30 mL). The mixture was stirred for 5 h, filtered, evaporated to dryness,
and the residue extracted with benzene (100 mL. 15 h), and filtered again. A
small amount of yellow crystals of 3 precipitated from the solution at 7°C.
Decomposition above 206'C. readily soluble in T H F and El,O, soluble in
benzene. almost insoluble in n-hexdne.
4 A solution of LiCECPh (1.3 g, 12 mmol) in ether (30 mL) was added to a
suspension of [CuBr(dms)] (0.56 g, 2.7 rnmol) in Et,O (50 mL) and heated under reflux for 2 h. The solvent was distilled off, the residue extracted with
benzene (60 mL) for 24 h under reflux, the resulting solution filtered and evaporated to dryness, and the residue taken up in Et,O (10mL) and cooled to
- 5 5 C. The yellow oil that separated was decanted off and dried under reduced pressure; it then appeared finely crystalline and colorless. Decomp.
above 8 0 ' C : extremely air-sensitive; readily soluble in T H F and Et,O, soluble
in beni.ene. Correct elemental analysis: ' H N M R (80 MHz, C,D,): b =7.697.34 (m. 17H: C,H,), 7.09-6.87 (m. 30H; C,H,), 3.40 (4, 1 2 H ; OCH,), 1.07
(1. 18H. CH,).
[17] P. P. Power, (The Structures of Organocuprates and Heteroorganocuprates and Related Species in Solution and in the Solid State). P r o p
lnorg. Chem. 1991, 39. 75.
[18] a) S. H. Bertz, G. Dabbagh, 1 Am. Chem. Soc. 1988, 110. 3668: b) B. H .
Lipshutz. S. Sharma. E. L. Ellsworth, hid. 1988, t10, 4032.
[19] Crystal structure analysis of tris(diethy1 ether)hexalithium deca(phenylethynyl)tetracuprate(r) (3): single crystals from benzene.
monoclinic, P2,/c, 2 = 4. u = 1763.6(3). b = 1938.3(3).
c = 2308.413) pm,
= 91.34(1)',
V =7889.2(2) x lo6 pm3. plrlLd=
1.288gcm-', IC =15.4cm-', crystal size 0.30x0.20x0.05mm3, Cu,,.
Enraf-Nonius C A D 4 diffractometer, temperature 173 K. range
2.25'' < 0 < 60.0. 7471 significant reflections (IF1 < 3 u ( / F l ) ) , direct
methods, 1105 refined parameters, R = 0.089, R, = 0.090 ( [ 0 2 ( F )
0.001 F 2 ] - ' . all non-hydrogen atoms refined with anisotropic temperature
[20] U. Schiimann, E. Weiss, Angew. Chem. 1988, 100. 573: Angen,. Chem. In!.
~ d Engl.
1988, 27, 584.
Received: February 5. 1993 [ZSSSl IE]
German version: Angew. ChPm. 1993, 105, 1136
[I] Gmefin Handbook of Inorganic Chemistr,r, Cu, Orgunocuppw Compounds,
Purr 3, 8th ed.. Springer, Berlin, 1986.
[2] J. G. Noltes, G. van Koten in Comprehensive Orgunometullic Chemiszry,
Vol. 2 (Eds.: G. Wilkinson, F. G. A. Stone. E. W Abel), Pergamon, New
York, 1982, p. 709 ff., and references therein.
[3] N. P. Lorenzen. E. Weiss. A n g e r . Chum. 1990. 102, 322; Angcw. Chem. Int.
Ed. Engl. 1990, 29, 300.
141 a) P. W. R. Corfield, H. M. M. Shearer, Absrr. Am. Crvsr. As.~oc.Meeting,
Bozeman. MT. USA, 1964, 96; b) M. L. H. Green. Orgunometullic Compounds Vol. 2: The Trunsrlion Elements, 3rd ed.. Methuen, London, 1968.
p. 271.
[5] F. Olbrich. U. Behrens, E. Weiss, unpublished.
[6] a ) A . E. Favorskii, L. Morev, 1 Russ. Phys. Chem. Sue. 1924, 18, 2496:
b) H. 0.
House. M. J. Umen, 1 Org. Chem. 1973.38, 3893; c) E. J. Corey,
D. Floyd, B. H. Lipshutz, ibid. 1978, 43, 3418.
[7] H. 0. House. C.-Y. Chu. J. M. Wilkins, M. J. Umen, 1 Org. Chem. 1975,
40. 1460.
[8] Crystal structure analysis of tetracosa[(trrt-butylethynyl)copper(i)].2nhexane (1): single crystals from n-hexane by slow cooling to 7°C and
concentration of the solution. C,,,H,,,Cu,;C,,H,,,
triclinic, Pf. Z = 1,
LI = 1419.1(2),
h = 1526.3(2), c = 2228.4(5) pm. I = 104.80(2), ,8 =
91.03(2). ;.=117.32(2)', V=4094(2)x106pm3, pcrlCd=1.478gcm-3,
p = 35.1 c m - '
(absorption correction), crystal size 0.20x0.25 x
0.27 mm3, Cu,,. Enraf-Nonius CAD4diffrdctometer. temperature 173 K,
range 2.25 < 0 <76.5', 13295 significant reflections ( I F / > 4a(lFl)),
structure solution with direct methods (SHELXS. G. Sheldrick,
Gottingen, 1986), 869 refined parameters, R = 0.047, R,, = 0.061
([u2( F ) + 0.0002F2]-1, all non-hydrogen atoms refined with anisotropic
tcmperature factors. I n the asymmetric unit i(CuC~CtBu),,.n-hexane)
the site of a rwr-butylethynyl ligand (C90-CY5) has 1 5 % bromide occupancy (Br90). The hexane molecule is disordered. Drawing: E. Keller,
SCHAKAL 88, Freiburg, 1988).
191 Further details of the crystal structure investigation may be obtained from
the Fachinformationszentrum Karlsruhe. Gesellschaft fur wissenschaftlich-technische Information mbH, D-76344 Eggenstein-Leopoldshafen (FRG) on quoting the depository number CSD-56987, the names of
the authors. and the journal citation.
[lo] M. Geissler. J. Kopf. B. Schubert, E. Weiss. W. Neugebauer, P von R.
Schleyer. Airgew. Chem. 1987, 99, 569; Angew. Chem. lnr. Ed. Engl. 1987,
26. 5x7.
[ l l ] N . P. Lorenzen, J. Kopf. F. Olbrich, U. Schumann, E. Weiss, ilngew. C/?em.
1990. 102. 1481: Angew. Chem. Int. Ed. Engi. 1990.29. 1441.
[12] M . 1. Bruce, M. G. Humphrey, J. G. Matisons, S. K. Roy, A. G. Swincer,
Aus!. J. Chem. 1984. 37, 1955.
1131 Ci-ystal structure analysis of tetrakis[(p,-rert-buty1ethynyl)triphenylphosphanecopper(1)].2Et,O (2): single crystals from ti-hexane. C,,H,,Cu,P,.
C,HL,O,, rhombohedra], P3, Z = 6, u = 1531.1(2). c = 6930(1) pm.
V =14069(3)x 10hpm3,d,,,,d =1.257 gcm-',p =13.8cm-',crystalsize
0.43 x 0.28 x 0.18 mm3. Mo,,. C A D 4 diffractometer, temperature 293 K.
range 2.25 < 0 < 25.0". 2377 significant reflections (14< 4a(lFI)),
direct methods, 402 refined parameters, R = 0.067, R, = 0.067 ( [ 0 2 ( F +
0.0006 F 2 ] - ' , all non-hydrogen atoms refined with anisotropic temperature factors. The site of a /err-butylethynyl ligand (C20-C25) has 25%
bromide occupancy (Br2). Both ether molecules are disordered; not all
atoms could be localized.
(141 L. Naldini. F. Demartin, M. Manassero, M. Sansoni, G. Rassu. M. A.
Zoroddu. J. Orgunomer. Chem. 1985, 279, C42.
[lS] M P. Gamasa. J. Gimeno. E. Lastra, X. Solans. J. Orgunomer. C h w .
[161 B. H. Lipshutz. R . S. Wilhelm, 1. A. Kozlowski (The Chemistry of Higher
Order Organocuprates), Terruhedron 1984. 40. 5005.
Angru.. C'hem. h.Ed. E d . 1993, 32. N o . 7
ansa-Metailocenes of Calcium and Strontium :
One-Pot Synthesis of Organometallic Complexes
of the Heavier Alkaline Earth Metals**
By Melanie Rieckhoff, Ursula Pieper, Dietmar Stalke,
and Frank 7: Edelmann*
Dedicated to Profissor Adorf Knappwost
on the occasion of his 80th birthday
Although [Cp,Ca] (Cp = $-C,H,) has been known since
1956,"' the organometallic chemistry of the heavier alkaline
earth metals slipped into obscurity for a long time. This field
gained new momentum only after the discovery of the hightemperature superconductors of the type YBa,Cu,O,-, .Iz1
In particular, the recent pioneering work of Hanusa et al.[31
has shown impressively that the organometallic chemistry of
the heavier alkaline earth metals is extremely interesting.
However, soluble organometalliccompounds of these metals
are still very rare; the decamethylmetallocenes [CptM]
(M = Ca, Sr, Ba; Cp* = $-C,Me,) and their adducts with
Lewis bases are among the most thoroughly studied example~.[~-''We now report an unusually simple, new route
to cyclopentadienylcalciurn and -strontium compounds as
well as the first X-ray structure determination of an ansametallocene derivative of calcium.
On addition of 6,6-dimethylfulvene to a suspension of calcium granules (activated by a small amount of HgC1,) in
THF, the colorless ansa-metallocene complex 1 is formed in
74% yield in a smooth reaction.
2:M = Sr. n = 2
Nonsolvated I forms extremely air-sensitive crystals that
are readily soluble in toluene and THE Activated strontium
[*] Priv. Doz. Dr. F. T. Edelmann, Dip1.-Chem. M. Rieckhoff, Dr. U. Pieper,
Dr. D. Stalke
Institut fur Anorganische Chemie der Universitlt
Tammannstrasse 4. D-37077 Gottingen (FRG)
Telefax: Int. code (551)39-3373
[**I This work was supported by the Fonds der Chemischen lndustrie and the
Deutsche Forschungsgemeinschaft.
mhH, 0-69451 Weinheim, 1993
0570-0833/93/0707-i079$ IO.OO+ .2S/O
powder reacts analogously with 6,6-dimethylfulvene to form
the likewise colorless bis(tetrahydr0furan) adduct 2 (38 %).
Finely divided barium does not react under similar reaction
conditions with fulvenes. The colorless complex 3 forms on
treatment of activated calcium with two equivalents of 6ethyl-6-methylfulvene. This product, however, crystallizes as
a nonseparable mixture of isomers, so the use of unsymmetrically substituted fulvenes does not offer any preparative
The reductive dimerization of fulvenes was recently reported for the lanthanide elements samarium and ytterbium,
too.[*] In fact, this is a good example of the known analogy
between the heavier alkaline earth metals and divalent
lanthanide~.~''The IR spectrum of 1 is almost superimposable on that of the analogous ytterbium(r1) compound
[{Me4C,(C,H4),)Yb].[81 This phenomenon has already been
discussed in detail for the complex pair [ (MeC,H,),M(dme)]
(M = Ca, Yb; dme = dimethoxyethane).l'O1
The example of the adduct formation of 1 and 3 with
I ,4-diazadienes shows that the ansa-metallocenes described
here can also undergo interesting reactions. Treatment of 1
with N,N'-di(terf-buty1)glyoxaldialdimine in THF/toluene
yields an air-sensitive, bright red I : 1 adduct 4.
Similarly, 3 reacts with N,N'-di(tert-buty1)glyoxaldialdimine to afford the red, crystalline complex 5, as a mix[{Me,Et,C,(C,H,),)Ca(tBuN=CHCH=NtBu)]
ture of isomers. Crystallization from toluene/hexane provided single crystals of 4 that were suitable for an X-ray structure analysis.["] Adduct 4 is monomeric in the solid state
(Fig. 1). The reductive dimerization of 6,6-dimethylfulvene
leads to the formation of the difunctional cyclopentadienyl
ligand [Me4C,(C,H4),]Z-. The average distance between the
centers of the rings and the calcium atom is 239.4 pm and is
thus comparable with the corresponding bond length in the
complex [ (MeC,H,),Ca(dme)] (239.9 prn)."Ol The diazadiene is coordinated to the central atom in the cis form as a
chelating ligand. As a result the calcium atom has a distorted
pseudo-tetrahedral coordination geometry. The angle between the calcium atom and the center of the rings is
119.0(5)". However, the N-Ca-N angle of 68.7(2)' is substantially smaller than the tetrahedral angle.
The reductive dimerization of 6,6-dialkylfulvenes by elemental calcium and strontium described here is probably the
simplest access to organometallic complexes of these elements. Furthermore, the compounds 1-5 are the first ansametallocene derivatives of the heavier alkaline earth metals.
Experimental Procedure
1: Granulated Ca (2.00 g. 49.9 mmol) was suspended in TH F (200 mL) under
an inert atmosphere (N,)and activated by addition of HgC1, (200 mg; without
stirring for 12 h followed by stirring for 1 h). While stirring and cooling (ice/salt
mixture) 6,6-dimethylfulvene (5.30 g, 49.9 mmol) [12] was added, and the mixture w d S allowed to warm slowly to room temperature. After 24 h stirrmg the
excess metal was filtered off, and the colorless filtrate was evaporated to dryness. The residue was dried for 2 h at 100°C under vacuum and subsequently
washed with two 150mL portions of hexane. Drying under vacuum (2h,
100 "C) yielded a colorless, very air-sensitive solid (4.66 g, 74%) that decomposed above 163°C. Correct C,H analysis. IR (Nujol): 3[cm-'] = 3075 s,
1613 m, 1302 ni, 1259 m, 1128 m, I099 m, 1029 vs, 879 m, 848 m, 724 vs,
697 m ; 'H NMR (250 MHz, [DJTHF): 6 = 6.06-5.97 (m. 4H, C,H,), 4.93
(m, 2H, C,H,), 4.48-4.42 (m, 2H, C,H,), 2.04 (m, 6H, Me), 1.21-1.15 (m,
6H, Me); EI-MS:m/i (%) 252 (16, M'), 147 (96, Me,CH(C,H,)Ca+), 107 (53,
Me,CH(C,H,)+), 91 (100. MeC(C,H,)+).
3: Analogously the reaction of Ca (2.00 g, 49.9 mmol) and 6-ethyl-6-methylfulvene (6.00 g, 49.9 mmol) yields a colorless, very air-sensitive solid (3.61 g,
52%). M.p. 170'C (decomp.); correct C,H analysis; IR (Nujol): G[cm-'] =
3074 rn,1610 m, 1260 m, 1096 m, 1029 w, 808 m, 724 vs; EI-MS: m/z (%) 280
(22, M i ) , 161 (100, MeEtCH(C,H,)Ca+), 131 (18, EtCH,C,(C,H,)+), 105
(18, EtC(C,H,)'), 93 (26, MeH,C(C,H,)+). The very complex 'H NMR spectrum indicates the presence of a mixture of isomers.
3: Activated strontium powder (1.41 g, 16.0 mmol) and 6,6-dimethylfulvene
(1.70 g, 16.0 mmol) were allowed to react for 48 h in TH F (50 mL). The suspension was filtered through a thin layer of Celite, the filtrate was evaporated to
dryness, and the residue washed with hexane (50 mL). Thorough drying under
vacuum afforded a colorless, extremely air-sensitive solid (1.33 g, 38%) that
decomposed above 181 "C. Correct C,H analysis. IR (Nujol): ij[cm-'] =
3068 m, 1669 m, 1616 m, 1261 s, 1097 vs, 1039 vs, 800 s, 748 vs, 723 vs; 'HNMR (250 MHz, C,D,/[D,]THF): 6 = 5.75 (m, 4H, C,H,), 5.14 (m, 2H,
C,H,), 4.63 (m, 2H, C,H,), 3.56-3.44 (m, 4H,THF), 2.15 (m, 6H, Me), 1.70
(m, 6 H , Me), 1.52-1.45 (m, 4H, THF); EI-MS: m/z(%)429(14, M + - CH,),
91 (100, MeC(C,H,)+).
4:A solution of l(2.00 g, 7.8 mmol) and (tBuN),C,H, (1.32 g, 7.8 mmol) [131
was stirred in THF (60 mL) for 2 h at room temperature. After addition of
toluene (40 mL), the THF was slowly removed under vacuum at 30°C. The
color changed from yellow to dark red. The solution was filtered, concentrated
to about 20 mL, and diluted with hexane (5mL). Cooling to -25°C afforded
red crystals (2.73 g, 83%). M.p. 157°C; correct C,H,N analysis; IR (Nujol):
i[cm-'] = 3071 vs, 1650m.1613 m, 1601 m, 1590111, 1385vs, 1366vs, 1238 s,
1226 s, 1202 s, 1127 s, 1116 s, 1099 s, 1052 s, 1039 vs, 971 vs, 927 m, 797 vs,
696 s, 466 m: 'H NMR (250 MHz, C,D,): 6 =7.11-7.00 (m, 2H, N = CH),
2.19-2.03 (m. 3H, Me), 1.88 (m, 3H, Me), 1.50-1.42 (m, 6H, Me), 1.07 (s,
Fig. 1. Structure of 4 in the crystal (one of two crystallographically independent molecules). Selected distances [pm] and angles I"]: Cal-Nl 250.3(6), CalN2 256.4(6), Cal-Xla 239.6(3), Cal-Xlb 239.1(3), C5-C6 152.9(10), C6-C9
159.1(11), C9-Cl2 152.8(10); NI-Cal-N2 68.7(2), (Xla , X l b =centers of Cp
0 VCH Verlagsgesellschuft mbH, 0-69451 Wemheim, 1993
18H, tBu); EI-MS: m/z (%) 212 (1, Me,C,(C,H,)~), 197 (3, Me,C,(C,H,):),
153 (18, C,H,N(CH),NC,H:),
141 (24, C,H,NH(CH),NCH,CH:),
112 (23,
C,H,N(CH),NH'), 97 (28, C,H,N(CH):), 57 (100, C,HZ).
5 is prepared analogously from 3 (2.00 g, 7.0 mmol) and (tBuN),C,H, (1.20 g,
7.0 mmol) to give 2.35 g of red crystals (75%). M.p. 166 "C; correct C,H,N
analysis; IR (Nujol): ij[cm-'] = 3075 s, 1651 m, 1611 m, 1590m, 1580111,
1345 m, 1304 m, 1240 m, 1220 m, 1200 m, 1097 m, 1056 s, 1029 s, 972 s, 803 s,
730 s ; 'H NMR (250 MHz, C,D,): 6 =7.07 (m, 2H, N = CH), 6.30-6.17 (m,
4H, C,H,). 5.20-5.08 (m, 2H, C,H,), 4.75 (m, 2H, C,H,), 1.88 (m, 3H,
CH,CH,), 1.76(m,3H,CH,CH3), 1.50-1.41 (m,6H, Me), 140-1.29(m, 2H,
CH,CH,), 1.05 (s, 18H. tBu), 0.90-0.81 (m, 2H, CH,CH,): EI-MS: m/z (%)
329 (26, [Me,C,H,(C,H,)ICa(C,H,NCH):),
280 (10, Me,Et,C,(C,H,)Ca '),
161 (90, MeEt,C,(C,H,)+). 57 (100, C,HZ).
$10.00+ ,2510
Received: January 9, 1993 [Z58031E]
German version' Angew. Chem. 1993, 10s. 1102
Angen. Chem. I n / . Ed. Engl. 1993, 32, N o . 7
K. Ziegler, H. Froitzheim-Kuhlhorn, H. Hafner, Chem. Ber. 1956, 89,
434 - 443.
I. G. Bednorz, K. A. Muller, Angew. Chem. 1988, 100,757-770; Angrw.
Chem. Int. Ed. Engl. 1988,27, 735-748.
T. P. Hanusa, Potyhedron 1990, 9, 1345-1362.
M. J. McCormick. R. A. Williams, L J. Levine. T. P. Hanusa, Polyhedron
1988, 7, 725-730.
C. J. Burns. R. A. Andersen, J. Orgunomef. Chem. 1987, 325, 31 - 37.
R. A. Williams, T. P. Hanusa, J. C. Huffman, Orgunomeiullics 1990, 9,
1128-1 134.
R. A . Andersen, R. R. Blom, C. J. Burns, H. V. Volden. J. Chem. SOC.
Chrm. Commun. 1987. 768-769.
A. Recknagel. F. T. Edelmann, Angew. Chem. 1991,103,720-721: Angew.
Cliem. Int. Ed. Engl. 1991, 30, 693-694.
W. J. Evans, Polyhedron 1987,6,803-835.
A. Hammel, W. Schwarz. J. Weidlein, J. Organomet. Chem. 1989, 378,
data for [Me,C,(C,H,),]Ca(fBuN=CHCH=NtBu) 4
( - 120'C): C,,H,,CaN,,
monoclinic, P2,/r, M = 420.68 gmol-', a =
2077.7(2), b =1769.3(3), c =1360.4(3) pm, fl =103.91(1~, V =
4.854 nm3, pcrlE,,= 1.15 gem-', F(000) = 1840, 2 = 8, ~(Mo,, graphite
monochromator, b =71.073 pm) = 0.27 mm-'. The data collection was
performed on a Siemens-Stoe AED2 diffractometer. Crystal size
0.3 x 0.3 x 0.4 mm; 8834 reflections of which 6422 were independent and
3927 observed with F > 4oF; 2@,,, = 45"; structure determination with
direct methods (SHELXS-92 [13]); refinement of 618 parameters with all
data and with 1060 restraints according to F 2 ; wR2 (all data) = 0.302,
R1 = 0.098. residual electron density 1.15 x 10' and -0.83 x 10' enm-3,
respectively. The asymmetric unit contains two crystallographically independent molecules. I n one, disorder in a Cp ring and a rotational disorder
of a tBu group was resolved and refined by using restraints (SHELXL-92
[14]). Further details of the crystal structure investigation may be obtained
from the Fachiuformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH, W-76344 Eggenstein-Leopoldshafen (FRG) on quoting the depository number CSD-57049. the
names of the authors, and the journal citation.
W. Freiesleben, Angew. Chem. 1963, 75,576; Angew. Chem. Int. Ed. Engl.
1963. 2, 396.
G. M. Sheldrick, Acfu CrystaNogr. Secr. A 1990, 46, 467.
114 G M Sheldrick, SHELXL-92, Gottingen, 1992
silylmethylcyclobutanes have been reassigned as silylcyclopentanes.[81Related reactions of allylstannanes with a$unsaturated acyliron complexes[9] and with aldehydes"']
have also been described. Currently we are investigating
metal-mediated processes for the construction of five-membered ring systems." 'I We report here on an elaboration of
the silylcyclopentane annulation, a novel [3 + 21 cycloaddition, which provides a versatile and useful method with
broad potential for the synthesis of cyclopentanoid natural
In our mechanistic proposal"' we suggested that a bridged
nonclassical pentavalent silicon cation"'] is the crucial intermediate in this novel cycloaddition. A stereospecific cyclization by intramolecular nucleophilic attack of the titanium
enolate at the carbon atom of the siliranium ion leads to the
product. Thus, the overall process may be regarded as a
sila-Wagner-Meerwein rearrangement. The same mechanism has been used to explain more recent examples.['] We
thought that variation of the alkyl substituents at the silicon
atom of the allylsilane would allow us to suppress nucleophilic attack at the silicon atom of the pentavalent silicon
cation and thus prevent the formation of the Sakurai
The allylsilanes that are not commercially available are
easily prepared by treatment of allylmagnesium chloride
with the appropriate trialkylchlorosilane (Scheme l)." 31 The
results of the reactions of cyclohexenyl methyl ketone with a
variety of allylsilanes 1 are presented in Table 1. Structural
assignments for the bicyclo[4.3.0]nonanes 2 are based on
X-ray crystal structure determinations for compound 2 dL8'
and the 2,4-dinitrophenylhydrazonederivative of 2a"' as
well as complete characterization by 'H and I3C NMR spectroscopy. In every example examined for the cyclopentane
annulation onto the six-membered ring (2a to 2i) under op-
A Versatile and Efficient Synthesis of Annulated
Cyclopentanes by Stereoselective 13 21 Cycloaddition of Allylsilanes and Cycloalkenyl Methyl
By Hans-Joachim Knolker,* Norbert Foitzik,
Helmut Goesmann, and Regina Gray
We recently reported". 2l that the "silyl-group-containing
by-products" of the Sakurai reaction,[31originally considare in fact silylcyclopenered silylmethylcy~lobutanes,~~~
tanes. This novel cylcopentane annulation involves a cationic 1,2-silyl shift,['] which proceeds stereospecifically, thus
generating three stereogenic centers. While the cyclization to
a silylcyclopentane in the course of the Sakurai reaction was
previously unprecedented, the formation of trimethylsilylcyclopentenes has been described for the reaction of
trimethylsilylallenes with enones.[61Following our first communication,"] more examples of silylcyclopentane formation along with Sakurai reaction products have been reported,"] and many of the products previously described as
Table 1. Optimization of the [3+2] cycloaddition of allylsilanes 1 to cyclohexenyl methyl ketone by variation of the substituents at the silicon atom [a].
[*] Prof. Dr. H.-J. Knolker. DipLChem. N. Foitzik, DipLChem. R. Graf
lnstitut fur Organische Chemie der Universitat der Universitiit
Richard-Willstiitter-Allee, D-76131 Karlsruhe (FRG)
Telefax: Int. code +(721)698529
Dr. H. Goesmann
Institut fur Anorganische Chemie der Universitiit Karlsruhe
[**I [3 21 Cycloadditions of Allylsilanes, Part 2. This work was supported by
the Deutsche Forschungsgemeinschaft (Gerhard-Hess-Forderpreis) and
the Fonds der Chemischen 1ndustrie.-Part 1 : [11.
Angew. Chem. Int. Ed. Engl. 1993, 32, N o . 7
Scheme 1.
59 [d]
Yield [%.I
53 fbl
70 [cl
[a] Unless otherwise noted all reactions were carried out according to an optimized standard procedure; after addition of the allylsilane the reaction mixture
was stirred for 19 h at -20°C (see Experimental Procedure). [b] The reaction
mixture was stirred for 19 h at -20°C and for another 24 h at O'C. [c] The
reaction mixture was stirred for 43 h at 0 "C. [d] Yield based o n dichlorodiisopropylsilane to which first 1.2 equiv phenylmagnesium chloride and then
1.2 equiv allylmagnesium chloride were added.
Verlugsge,rell.~chafimbH, 0-69481 Weinheim, 1993
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ansa, strontium, complexes, earth, organometallic, synthesis, heavier, one, metali, metallocene, pot, calcium, alkaline
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