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Diastereo- and Enantioselective Aldol Reactions via -Silyl Ketones Asymmetric Synthesis of the Aggregation Pheromone Sitophilure.

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1 : A mixture of [{(C,M~,)RUCI~}~]
(6.60 g, 9.87 mmol) and dimethyl phosphite (40 m L ) in methanol (500 mL) was heated under reflux with stirring for
4 d until the initially red solution had turned yellow in color. On subsequent
evaporation of the solution under high vacuum a yellow precipitate separated out, which after addition o f 100 mL of dichloromethane went into solution again. The solution thus obtained was extracted with 6 x 15 mL of water to remove hydrochloric acid and any unchanged dimethyl phosphite. On
removal of the solvent the product precipitated out as a yellow powder. Yield
9.75 g (95%). Recrystallization from dichloromethane/hexane afforded fine
yellow crystals. ' H - N M R (80 MHz, CDC13): 6=2.1 (t. 4J(PRuCCH)=0.9
Hz, l8H;CCH,),3.59(virt.t,~J(POCH)=lI.l
'J(POCH)= 10.3 Hz, 6 H : OCH3), 12.7 (br. s, 1 H ; PO-H).
3 : A suspension of 1.50 g (2.9 mmol) of 1 in 20 m L of water was treated with
570 mg (2.9 mmol) of C U ( O A C ) ~ - H and
~ O the resulting mixture stirred for
4 h. The product was centrifuged off, washed twice with a small amount of
water and dried under high vacuum. Yield 1.49 g (94%). After recrystallization from dichloromethane/pentane, analytically pure yellow crystals were
4 : A mixture of 3 (150mg, 0.14mmol) and copper powder (200mg,
3.15 mmol) in 15 m L of methanol was stirred under a CO-atmosphere until
the copper(i1) complex had completely dissolved (ca. 3 h). The yellow solution was separated from the excess metal under a C O atmosphere and then
evaporated to dryness. The yellow solid product was dried for 1 h under high
vacuum. Yield 135 mg (81%). IR (CH,OH): 2089 c m - ' (s, v ( C 0 ) ) .4 is readily soluble in methanol and dichloromethane and insoluble in saturated hydrocarbons. I t decomposes on exposure to air, rapidly in methanol, but more
slowly in dichloromethane and in the solid state.
Received: November 19, 1987 [ Z 2504 IE]
German version: Angew. Chem. 100 (1988) 603
a) W. Klaui, A. Muller, W. Eberspach, R. Boese, 1. Goldberg, J. Am.
Chem. Soc. 109 (1987) 164, and references cited therein; b) W. Klaui, E.
Buchholz, unpublished.
We have found such adducts of NaI and NaPF, with
Na[(C,Me,)RuC1{P(0)(OMe)2}2] and analogous compounds, e.g.
and N~[(C,H,)RUI,(P(O)(OM~)~]].See
also the structure determination of Na[(C,H6)OsI(P(0)(OMe)2]2], which
crystallizes in a disordered fashion with one equivalent of NaI: U. Schubert, R. Werner, L. Zinner, H. Werner, J Organomet. Chem. 253 (1983)
2 : ' H - N M R (80 MHz, CDCI3): 6=2.0 (t, 'J(PRuCCH)=0.8 Hz, 1 8 H ;
CCH2), 3.48 (virt. t, 'J(POCH)= 10.5 Hz, 6 H : OCH3), 3.50 (virt. t,
'J(POCH)= 10.1 Hz, 6 H ; OCH,).
M. I. Bruce, J . Organornet. Chem. 44 (1972) 209, and references cited
M. Pasquali, C . Floriani, A. Gaetani-Manfredotti, Inorg. Chem. 20 (1981)
3382. A value of 2120 cm-' is quoted for the <CO) frequency of solventfree [Cu(CO)Cl] in Nujol.
enantiomerically pure a-trialkylsilyl ketones and a-trialkylsilylaldehydes.[41We have now found that a-silyl ketones of type 1 can be employed as chiral methylene compounds in aldol reactions and enable the stereoselective
synthesis of syn-configurated 0-hydroxyketones 4 in high
diastereomeric and enantiomeric excesses.
iPr,NEt, CH,C1,.
-10°C,2 h
By Dieter Enders* and Braj Bhushan Lohray
Dedicated to Professor Helmut Dorfel on the occasion of
his 60th birthday
Diastereo- and enantioselective aldol reactions have
been the subject of intensive study in recent years."]
Whereas excellent diastereo- and enantioselectivities have
been achieved with aldol-like processes that lead to hydroxycarboxylic acids and their derivatives,I2' direct aldol
syntheses of 0-hydroxyketones are less widely developed
and, in part still unsatisfactory with regard to enantiomeric
We recently reported on a facile entry to highly
Prof. Dr. D. Enders, Dr. B. Bhushan Lohray
Institut fur Organische Chemie der Technischen Hochschule
Professor-Pirlet-StrasseI, D-5100 Aachen (FRG)
This work was supported by the Fonds der Chemischen Industrie a n d
by BASF AG, DEGUSSA AG, Bayer AG, and Wacker Chemie
Angew. Chern. In,. Ed. Engl. 27 (1988) No. 4
2OoC. 1-2 d
1. RCHO.-78'C
d e r 92-90%
eel 98%
For example, (R)-2-(tert-butyldimethylsilyl)pentan-3one, (R)-1, was converted by reaction with di-n-butylboryl
triflate in dichloromethane in the presence of Hunig base
into the boron enolate ( R ) - 2 and then allowed to react
with aldehydes at - 78°C. Subsequent oxidative work-upl']
and flash chromatography furnished the syn-aldol adducts
3, which could be desilylated with 60%aqueous tetrafluoroboric acid in T H F to the syn-aldol products 4 with high
diastereomeric (de: 92 to 298%) and enantiomeric purity
(ee 2 98%) (Table 1).
Table I . b-Hydroxy ketones syn-4 prepared by diastereo- and enantioselective aldol reaction with (R). o r (S)-l.
yield 1%)
4b [fI C2Hs
Diastereo- and Enantioselective Aldol Reactions via
a-Silyl Ketones, Asymmetric Synthesis of the
Aggregation Pheromone Sitophilure **
(c, solvent)
[%/.I [a1
- 30.0 [d]
(1.4, ether)
-28.0 [el
(1.2, ether)
(1.0, ether)
+ 33.95 [g]
(0.94, CHC13)
(1.0, ether)
- 16.0
(1.3, benzene)
2 98
2 98
2 98
2 98
[a] Determined "C- and I9F-NMR spectroscopically via the corresponding
(S)-MTPA ester [71 (MTPA= Ph-C(OCH,)(CF,)-CO,H).
[b] Determined as
in [a] and also 'H-NMR spectroscopically with Eu(hfc), as well as polarimetrically by comparison with literature data [9, 10, 3 h]. [c] Assignment based
on a comparlson with data in the literature [9, 10,3 h]. [d] In [91: [a16= -30.2
( c = 1.43, ether). [el Contaminated with 2% anti-isomer (4S.59-4b; in [lo]:
-26.7 (c= 1.52, ether). [fI (S)-1 was used as chiral methylene component. [g] -2.14 (c= 1.0, ether); ( 4 S S R ) - k [3 hl: [a]E=-23.2 (c= 1.8, CHCI,)
corresponding to 66Oh ee; the change in sense of rotation on changing the
solvent from ether to chloroform is typical for the aldol adducts syn-4 ; we
thank Dr. I. Palerson. Cambridge, for helpful discussions. [h] Confirmed by
X-ray structure analysis of the corresponding SAMP-hydrazone [3d, 1 I].
The simple diastereoselectivity of the aldol C-C coupling can be determined 'H, and I3C-NMR spectroscopically at the stage of the crude adducts 3. The syn :anti ratio
is ca. 9:1, irrespective of the aldehyde employed. From
this and from the I3C-NMR spectroscopic and gas-chro-
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58 1
matographic monitoring of ( R ) - 2 after conversion into the
corresponding trimethylsilyl enol
we derive a Z : E
ratio of ca. 9 : 1 in the case of ( R ) - 2 .The high enantiomeric
purity (ee298Y0) of the syn adducts 3 and 4 was determined NMR spectroscopically via the corresponding (S)MTPA ester"] ( I3C,l9F) and by shift experiments [with
Eu(hfc),], as well as polarimetrically (4). The agreement in
the de and ee values provides proof of an epimerizationfree and racemization-free desilylation. The absolute configurations of the a-hydroxy ketones 4 quoted in Table 1
are based on a comparison of the polarimetric data with
data in the literature. As expected, the use of the (S)-configurated methylene components (S)-1 leads to the other
syn-enantiomer (4b, Table 1).181
The stereochemistry of the diastereo- and enantioselective C-C coupling is consistent with a six-membered transition state in the sense of the Zimmermann-Traxler modIn the case of 4a and 4b, the chromatographically
separated anti-isomers that are formed in small amounts
could each be assigned the (4S,SS)-configuration
( e e 2 98%) on the basis of the l3C-NMR spectra.'"] Accordingly, in the case of aliphatic aldehydes the transition state
Tz leads to the syn isomers with (4R,5S)-configuration,
and TE to the anti isomers with (4S,5S)-~onfiguration.['~]
An exception is the benzaldehyde adduct 4e, which according to an X-ray structure a n a l y ~ i s ~ of
~ ~the
, " ~corre-
tively, thus demonstrating the preparative value of this
new variant of the aldol reaction.
A stirred solution of 12 mmol of ethyl diisopropylamine in 25 mL of dichloromethane was treated under an argon atmosphere at - 10°C with 11 mmol
of di-n-butylboryl triflate Zb, and then dropwise with a solution of 10 mmol
of (R)-1 in 10 mL of dichloromethane. After two hours' stirring at - 10°C
the reaction mixture, which now contained the boron enolate ( R ) - 2 , was
cooled to -78°C and treated with I0 mmol of aldehyde (in the case of enolizable aldehydes: 12-15 mmol dissolved in 20-30 mL of dichloromethane).
The mixture was stirred for a further 0.5 h at - 78°C and I h at 0 ° C and then
subjected as follows to oxidative work-up in analogy to the method used by
Euans et al.'", in the case of aromatic aldehydes with 30% H 2 0 2 (without
sodium hydrogencarbonate solution), in the case of enolizable aldehydes
with MoOS.pyridine.HMPA (MoOPH) [17]: the resulting di-n-butylalkoxyborane that was formed was oxidized by addition of 15 mmol of MoOPH at
0°C. The yellow reaction mixture was stirred for 0.5 h at 0°C and 1 h at room
temperature and then treated with 100 mL of pH7-buffer solution. After
15 minutes' stirring, the organic phase was separated off and the aqueous
phase extracted twice with dichloromethane. The combined organic phases
were washed twice with 100 mL of ice-cold 0.5 N HCI and once with saturated NaCl solution, and dried over magnesium sulfate. Removal of the solvent afforded the crude aldol adducts 3 as a syn/anti mixture (ca. 9 : 1) which
was separated by flash chromatography (silica gel, ether/n-pentane 114,
R,(syn)>R,(anti)). A stirred solution of 10 mmol of pure syn-adduct 3 in
50 mL of T H F was treated at room temperature with 10 mL of 60% tetrafluoroboric acid. After 1-2 days stirring' the T H F was removed and the residue extracted with 3 x I00 mL of ether. The combined ether phases were
washed with 5% sodium hydrogencarbonate solution and dried over magnesium sulfate. Removal of the solvent and chromatographic purification (silica gel, ether/n-pentane 1/4) furnished syn-4.
Received: January 8, 1988 [Z 2565 IE]
German version: Angew. Chem. 100 (1988) 594
CAS Registry numbers:
(R)-I, 107496-27-5; (S)-l, 107496-28-6; (R)-2, 113569-02-1; (S)-2, I13569-087; 3a, 113569-03-2; 3b (isomer I), 113569-04-3; 3b, (isomer 2), 113626-44; 3c,
113569-05-4; 3d, 113569.06-5; 3e, 113569-07-6; 4a 108161-63-3; 4b (isomer I),
108815-20-9; 4b (isomer 2), 108815-23-2; 4c, 113626-45-2; 4d, 113626-46-3;
4e, 107242-72-8; H,CCHO, 75-07-0; C 2 H S C H 0 , 123-38-6: I-C3H7CH0, 7884-2; C6H5(CH2)2CH0,104-53-0; C,,H5CH0, 100-52-7.
sponding SAMP-hydrazone has the enantiomeric (4S,5S)configuration based on Tz/TE.I'41The correlation between
the Z/E ratio of the boron enolate and the syn/anti ratio
of 4 (in each case 9 : 1) indicates a virtually complete asymmetric induction.
Rice weevils (Sitophilus oryzae L.) and maize weevils (S.
zeamis Motsch) cause some hundreds of millions of dollars
worth of damage per annum in the storage of grain. The
aggregation-promoting pheromone of these insects was recently identified as syn-5-hydroxy-4-methylheptan-3-one
(4b) (sitophilure) and has been synthesized; its absolute
configuration is still u n k n o ~ n . ~ ' ~Starting
from (R)-1
and (S)-l,we have prepared both enantiomers of sitophilure, (4R,5S)-4b and (4S,5R)-4b, in total yields of 58-62%
and high diastereomeric and enantiomeric purity, respec-
[I]Reviews: a) D. A. Evans, J. V. Nelson, T. R. Taber, Top. Stereochem. 13
(1982) I ; b) T. Mukaiyama, Org. React ( N Y ) 28 (1982) 203; c) C. H.
Heathcock in J. D. Morrison (Ed.): Asymmetric Synthesis. Yo/. 3, Academic Press, Orlando, FL, USA 1984, pp. 1 11-212; d) S. Masamune, W.
Choy, J. S. Petersen, L. R. Sita, Angew. Chem. 97 (1985) 1 ;Angew. Chem.
I n t . Ed. Engl. 24 (1985) 1 , e) M. Braun, hid. 99 (1987) 24 and 26 (1987)
[2] Examples: a) S. Masamune, W. Choy, F. A. J. Kerdesky, B. Imperiali, J.
Am. Chem. Soc. 103 (1981) 1566; b) D. A. Evans, J. Bartroli, T. L. Shih,
ihid. 103 (1981) 2127; c) T. Mukaiyama, N. Iwasawa, R. W. Stevens, T.
Haga, Tetrahedron 40 (1984) 1381; d) A. 1. Meyers, Y. Yamamoto, ibid.
40 (1984) 2309; e) G . Helmchen, U. Leikauf, 1. Taufer-Knopfel, Angew.
Chem. 97(1985) 874; Angew. Chem. I n t . Ed. Engl. 24 (1985) 874; f) C.
Gennari, A. Bernardi, L. Colombo, C. Scolastico, J. Am. Chem. Soc. 107
(1985) 5812; g) W. Oppolzer, J. Marco-Contelles, Helu. Chim Acta 69
(1986) 1699; h) S. Masamune, T. Sato, B. M. Kim, T. A. Wollmann, J.
Am. Chem. SOC.108 (1986) 8279.
131 a ) H. Eichenauer, E. Friedrich, W. Lutz, D. Enders, Angew. Chem. 90
(1978) 219; Angew. Chem I n t . Ed. Engl. 19 (1978) 206; b) N. Iwasawa,
T. Mukaiyama, Chem. Lett. 1982. 1441 ; c) S . H. Mashraqui, R M. Kellogg, J. Org. Chem. 49 (1984) 2513; d ) D. Enders, Chem. Scr. 25 (1985)
139; e) K. Narasaka, T. Miwa, Chem. Lmr. 1985, 1217; 0 H.-F. Chow, D.
Seebach, Helo. Chrrn. Acta 69 (1986) 604; g) M. T. Reetz, F. Kunisch, P.
Heitmann, Tetrahedron Lett. 27 (1986) 4721; h) I. Paterson, M. A. Lister,
C. K. McClure, rbid. 27 (1986) 4787; i) 1. R. Silverman, C. Edington, J.
D. Elliott, W. S. Johnson, J . Org. Chem. 52 (1987) 180.
[4] D. Enders, B. Bhushan Lohray, Angew. Chem. 99 (1987) 359: Angew
Chem. Inr. Ed. Engl. 26 (1987) 35 I .
[5] D. A. Evans, J. V. Nelson, E. Vogel, T. R. Taber, J. Am Chem. SOC. 103
(1981) 3099, and references cited therein.
[6] In the conversion of (R)-Z into the trimethylsilyl enol ether a partial Z / E
isomerization could not be avoided.
[7j J. A. Dale, H. S. Mosher, J. Am. Chem. SOC.95 (1973) 512.
[S] In the meantime we have confirmed the absolute configuration of the
a-silyl ketones of type 1 [4] by X-ray structure analysis of a crystalline
c H,
( I R . 5.5)-4b
de? 96%. ee? 98%
(LS,5Rl- 4b
[*] Note added in proof: Another synthesis of this enantiomer has been re-
ported recently: G . Fuganti, H. E. Hoberg, G. Pedrocchi-Fantoni, S . Servi, Chem. Lett. 1988, 385.
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Angew. Chem. I n / . Ed. Engl 27 (1988) N o . 4
SAMP-hydrazone. D. Enders, B. Bhushan Lohray, W. Hesse, M. Jansen,
K. Mori, T. Ebata, Tefruhedron 42 (1986) 4413.
a) K. Mori, T. Ebata, Tetruhedron 42 (1986) 4421; b) A. Fauve, H. Veschambre, Tefruhedron Lett. 28 (1987) 5037.
U. Baus, Dissertation, Universitat Bonn 1985.
H. E. Zimmermann, M. D. Traxler, J . Am. Chem. SOC.79 (1957) 1920.
For the mechanism of boron enolate aldol additions, see: R. W. Hoffmann, K. Ditrich, S. Froech, Tetruhedron 41 (1985) 5517; b) C. H.
Heathcock, S . Arseniyadis, Tefruhedron Left. 26 (1985) 6009; c) C. Gennari, R. Todeschini, M. G. Beretta, G. Favini, C. Scolastico, J . Org.
Chem. 5 1 (1986) 612; d) R. W. Hoffmann, K. Ditrich, S. Froech, Liebigs
Ann. Chem. 1987. 977; e) J . M. Goodmann, 1. Paterson, S. D. Kahn,
Tetruhrdron Len.. in press; we thank Dr I . Pulerson, Cambridge, for
supplying a preprint.
We habe already observed a change in the simple diastereoselectivity in
previous studies on changing from aliphatic t o aromatic aldehydes in
aldol reactions via lithiated SAMP-hydrazones under otherwise the
same conditions [ I I]; an explanation is still lacking.
N. R. Schmuff, J. K. Phillips, W. E. Burkholder, H. M. Fales, C.-W.
Chen, P P. Roller, M. Ma, Tefruhedron Lett. 25 (1984) 1533.
All the new compounds gave correct elemental analyses and characteristic spectra.
E. Vedejs, D. A. Engler, J. E. Telschow, .I.
Org. Chem. 43 (1978) 188.
Synthesis and Structure of
I( OCkFe=Si= Fe(CO), . 2(Me2N)3POja Complex of Formally Zerovalent Silicon**
geometry. An indication of the unusual bonding of the silicon is already provided by the increased coupling constant 3J(3’P’H)=23.3 Hz.I4I The vibration spectra show the
typical bands for terminal trigonal-pyramidally (tbp) coordinated Fe(CO), moieties.‘41 Two bands of equal intensity
are observed both for the vpo- as well as for the vco;,,vibrations; this is fully consistent with the C, symmetry of
the complex.15’The X-ray structure analysis[61confirms the
proposed structure (Fig. 1). The molecule has approxi-
By Christian Zybill,* Dallas L. Wilkinson, and
Gerhard Miilier
Recently, it has been demonstrated that silanediyl(si1y1ene)-transition metal complexes ( A ) are stable as weak
donor adducts.“] In contrast, p-Si complexes ( B ) with formally zerovalent silicon and allene-like structure have
hitherto defied isolation. Analogous compounds of the
higher homologues germanium and lead, on the other
hand, are already known.”] We now present the diiron
complex 4 as first example of a donor-stabilized silicon(0)
complex of type B.
The synthesis of compounc 4 was accomp-shed by
reaction of disodiumtetracarbonyl ferrate 1 with silicon tetrachloride 2 in an appropriate donor solvent.[31The reaction presumably proceeds via the silanediyl complex 3 as
After chromatographic separation and crystallization
from THF, 4 is obtained as colorless, moderately air- and
moisture-sensitive crystals. The silicon complex of type B
primarily differs from the well-known analogous coordination compounds of germanium and lead‘’] with “naked”
elements of group 14 by the increase in coordination number of the silicon from 2 to 4 and by the almost tetrahedral
[‘I Dr. C. Zybill, Dr. D. 1.Wilkinson [+I, Dr. G. Miiller
Anorganisch-chemisches Institut der Technischen Universitat Miinchen
Lichtenbergstr. 4, D-8046 Garching (FRG)
Permanent address:
Monash University, Clayton, Victoria (Australia)
This work was sponsored by an Alexander-von-Humboldt fellowship (D.
L. W.i. We thank Prof. H . Schmidbuur for support of this work.
Angew Chem l n f Ed Engl 27(1988) No. 4
Fig. 1. Crystal structure of 4 - T H F (ORTEP, displacement ellipsoids at the
50% probability level, methyl groups with arbitrary radii, without H-atoms
and THF). Important bond lengths [A] and angles [“I: Si-Fel 2.339(1), Si-Fez
2.341(1), Si-01 1.745(2), Si-02 1.748(3), PI-01 1.530(2), P2-02 1.526(3), FelC13 1.769(3), Fel-C14 1.760(3), Fel-CIS 1.783(4), Fel-C16 1.788(5), Fe2-CI7
1.782(4), Fe2-Cl8 1.762(4), Fe2-Cl9 1.787(4), Fe2-C20 1.753(6); Fel-Si-Fe2
122.6(1), 01-Si-02 92.1(1), Fel-Si-OI 1 l0.6(1), Fel-Si-02 107.6(1), Fe2-Si-Ol
109.2(1), Fe2-Si-02 1 10.4(1), Si-01-PI 160.7(2), Si-O2-P2 167.1(1).
mately C2 symmetry; the silicon atom is bound to two
Fe(CO), fragments and occupies an axial position of the
tbp-configurated iron atoms. Long donor contacts to the
oxygen atoms of the two HMPT molecules complete a distorted tetrahedral coordination of the silicon atom. A striking feature of the structure is that the Fel-Si-Fe2 angle
(122.6(1)”) is significantly widened at the expense of the
01-Si-02 angle (92.1( l)O), whereas the remaining angles
deviate only slightly from the normal tetrahedral angle.
The two Fe-Si bonds are almost equal in length (Si-Fel
2.339(1), Si-Fe2 2.341(1)
and somewhat longer than the
Si-Fe “double bond” in [(OC)4Fe=Si(OtBu)2. HMPTj
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sitophilus, asymmetric, synthesis, reaction, aldon, ketone, enantioselectivity, diastereo, sily, aggregation, via, pheromones
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