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Asymmetric Epoxidation of Enones With Oxygen in the Presence of Diethylzinc and (R R)-N-Methylpseudoephedrine.

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ably expected based on the different coordination of aldehydes
and trui~simines to the boron atom in chairlike transition state
structures (cf. the two chair transition state structures in
Scheme 5 ) . However, the stereodivergence caused by the type of
thioester (COSPh vs. COStBu) in the addition to imines is quite
surprising. The stereochemical outcome can be rationalized by
using corresponding chair and boat transition structures
(Scheme 5).r1q1However, there is no obvious explanation why
this strong stereocontrol is operating as a function of R2. Experiments not reported here show that the role of the oxygen protecting group R ' is relatively minor.
OR'
$
GBBr (ent-5)
R'OCH,COSR~
SR'
- L '
EtSN
+o
-
I
L'
H
I *
OR'
[7] For related chemistry involving silyl ketene acetal additions to chirdl imines
mediated by a chiral boron Lewis acid. see: a) K . Hat'ori. M Miyata. H.
Yamamoto. J. Air7 C/imi. Sor. 1993. //S.1151 1152. h) K. Hattori. H. Yamamoto. 7irtrobeilron 1994. 50. 2785 2792
[XI Prepared from methyl glycolate in two steps. a ) tBuSH. AIMe,. hexanes.
CH,CI,. 0 C. 53%: b) PhCOCI. Et,N. 4-(dimethylamino)pyridine. CH,CI,.
0 C. 89%.
191 D. J. Hart. K Kanai. D G . Thomas. T. K. Yang. J. Or? C/iuni. 1983, 48.
289- 294.
[lo] a ) M. E. Bunnage. S G. Davies. C. J. Goodwin, J. Cberii. .SO< f d m Zons. f
1993.1375 1376: b) ;b;d 1994,2385-2391 : c) JLN. Denis. A E . Greene. A. A.
Serrd. M.-J Luche, J Org. Cbein. 1986. 8f. 46 50.
[ I t ] The .srii:wiri mixture was used in the next synthetic step The . s n i and rrntt
compounds were separated and isolated only for analytical purposes.
[ 121 Compound 7 was transformed into the known (-)-methyl 12R.3S)-3-benzoylamino-2-hydroxy-3-phenylpropionate
by the following steps' a ) 30% H,O,
(4equiv). LiOH aq. (Xequiv). THF. 0 C. 15 h; Na,SO,. b) CH,N,. Et,O.
MeOH. For optical rotation values, see. a) M. C. Wani, FI L Taylor. M. E.
Wall. P Coggon. A. T. McPhail, J. Am C/icni. Soc. 1971. 93. 2325- 2326: b)
J - N . Denis. A. Correa. A. E. Greene. J Or,? Cbivi. 1990. 55. 1957-1959: c)
refs. [10b.c]
[I31 Determination of the absolute configuration by means 0 1 the Mosher method
(a) I. Ohtani. T. Kusumi. Y. Kashman. H Kakisawa. J A,,, Chrn? Soc. 1991,
113. 4092-4096; b) S Izumi. H Monyoshi, T Hirata. Bid/. Cberir So<..Jpn.
1994.67.2600- 2602) was in accord with the determination b? chemical correlation.
[I41 Prepared from methyl glycolate in two steps: a ) TBDMSCI. imidazole, DMF,
0 C to room temper2iture. 100%; b) PhSH. AIMe,3.hexanes. CH,CI,. 0 C to
room temperature. 79%.
[IS] D.-M Gou. Y-C Liu, C.-S. Chen. J Org C h i n . 1993. i X . 1287-1289.
1161 Compound I 1 was transformed into the known (+)-methyl (2S.3.S)-3-benroylamino-2-hydroxy-3-phenylpropionateby the follov.ing steps a ) 30%
H,O, (4equiv). LiOH aq. (2equiv). THF. 0 C. 15 h: Na,SO,: b) CH,N,,
Et,O. MeOH. For optical rotation values, see. a) F. A Davis. R. T Reddy,
R. E. Reddy. J Org. Cbeni. 1992. 87. 6387-6389: b) ref. [lob]
1171 F. Gueritte-Voegelein. V. Senilh. B. David. D. Guenard. P Potier. fi,rrri/ier/ron
1986. 42.4451 -4460.
1181 T. C Bruice. S J. Benkovic. Bioorgrrrii< Mochmii.~ni.~
W A Benjamin Inc.. New
York. 1966. Vol. I. Chapter 3.
[I91 Recent abinitio MOcalculations(3-21G hasisset) featuring the addition ofthe
BH, enol borinate derived from acetaldehyde to formaldehydeimine have
shown that two competing cyclic transition structures are important. the chair
and the boat (A Bernardi. C Gennari. L. Raimondi. M Villa (University of
Milano). unpublished results).
~
- RnSR2
OH 0
anb
R2=Ph, 1Bu
L'
Ph
R'O
H
OR'
L^
\ - p
OR'
PhCH=NSiMe3
NH, 0
R'=Ph
SiMe,
anfi
Scheme 5. Transition state models for the boron aldol addition to imines. Products
with m t i configuration arise from attack on the Re face of the aldehyde or imine.
products with s i x configuration from attack on the Si face.
Received. February 28. 1996 [28880IE]
German version: Aiigeii'. Chrm 1996, 108. 1809-1812
Keywords: asymmetric syntheses
thioesters
- enolates -
imines
*
taxol
.
[I] Taxol is the registered trademark of Bristol-Myers Squibb Company for Paclitaxel For a review. see: K C. Nicolaou. W.-M. Dai, R. K. Guy. Aiiguii. Chrm.
1994. 106. 38 67: Angen.. Cliem. In/ Ed Eng/. 1994. 33, 15-44.
[I] a ) J -N. Denis. A E. Greene, D. Guenard. F. Gueritte-Voegelein, L. Mangatal.
P Potier. J .4rn Cl7c.m. Soc 1988, 110, 5917-5919: b)A. Commercon, D.
Berard. F. Bernard. J D. Bouzard. Tetmhedron Lett 1992, 33. 5185-5188;
c) J N. Denib. A M Kanazdwd, A E Greene, ibid. 1994. 38. 105-108:
(Rh6ne-Poulenc Rorer S.A.). WO 94:10169. 1994, FR-A 92:13000. 1992.
d ) A M Kanazawa. J N. Denis. A E Greene. J: Cheni. Soc Clirm. Cornn?uii
1994. 2591 2592
[3] D. G. I Kingston, A. G. Chaudhary. A A L. Gunatilaka, M L. Middleton.
E,/rii/ieilroti L c r i 1994. 35. 4483-4484.
141 a ) K.A. Holton. EP-A 400971, 1990 [Cbum. Absrr. 1991. 114. 164568ql: US
5015744.1991:US5136060.1992:US5175315.1992:W093~06079,1993:US
5229526. 1993. h) I. Ojima. I. Habus. M Zhao. M Zucco. Y. H Park. C M.
Sun. T Brigaud. G r r ~ i / i ( v / r i r i 1992.48,
?
6985-7012; c) 1. Ojima. C. M. Sun. M.
Zucco. Y. H. Park. 0 Duclos, S Kuduk, Trtrnhei/ron Lett 1993, 34, 41494152: d ) I . Ojima. WO 94 18164. 1994: US Serial N. 93,11922. 1993: e) R. A.
Holton. K . Rengdn. H. Nadizadeh, US 5283253. 1994.
151 C Gcnnari. N Mongelli. E. Vdnotti. A Vulpetti (Pharmacia). GB-A
9512471.5. 1995
161 a ) C Gennari. C. T. Hewkin. F. Molinari. A. Bernardi. A Comotti. J. M .
Goodman. I Paterson. J Urg. Cbem. 1992.57. 5173- 5177; b) C Gennari, D.
Moresca. S Vieth. A Vulpetti, Aiigrii.. Cbein. 1993. 105. 1717-1719: Angeir
C/iciii Iiit E d EngI. 1993, 32. 1618-1621: c ) C . Gennari, A. Vulpetti. D.
Moresca. P r r d i d r o f i Lrrr. 1994. 35. 4857 -4860: d ) A. Bernardi. C. Gennari.
J. M . Goodman. I . Paterson, T e r r d i d r o i i A.\~.mn?ivrj.1995, 6. 2613-2636.
cl C' Gennai-i. < i . Pain. D Moresca J Or,y Chmi. 1995. 60. 6248--6249.
Asymmetric Epoxidation of Enones With
Oxygen in the Presence of Diethylzinc and
(R,R)-N-Methylpseudoephedrine**
Dieter Enders,* Jiqun Zhu, and Gerhard Raabe
The asymmetric epoxidation of C - C double bonds plays an
important role in the synthesis of optically active organic compounds. In 1980 Sharpless et al. reported the titanium-mediated
enantioselective epoxidation of allylic alkohols with tBuOOH,"!
which was later achieved catalytically by addition of molecular
sieves.[21Based on cationic salen - manganese complexes Jacobsen et aI.c3]and Katsuki et al.[4!developed an efficient method
for the enantioselective epoxidation of unfunctionalized olefins.
[*I Prof. Dr. D. Enders. Dr. J. Zhu, Dr. G. Raabe
Institut fur Organische Chemie der Technischen Hochschule
Professor-Pirlet-Strasse I . D-52074 Aachen (Germany)
Fax- Int. code +(241)8888 127
e-mail: endersgi rwth-aachen.de
["*I This work was supported by the Fonds der Chemischen Industrie. the Deutsche
Forschungsgemeinschaft (Leibniz Prize). and the European Union (HCM network: Metal Mediated and Catalysed Organic Synthesis). We are obliged to the
companies Degussa AG. BASF AG, Bayer AG. Hoechst AG. and Knoll AG
for donations of chemicals.
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The asymmetric epoxidation of chalcone in high optical yields
was achieved by JuliL et al. with H,O,,"aOH
in a three-phase
system over chiral polypeptides.['I However, the success of this
method is as yet usually limited to chalcones.["l Other methods
for the enantioselective epoxidation of +unsaturated ketones,
for example by use of benzylquininium chloride.['1 bovine serum
albumin.l81 cyclodextrins,'"] or chiral platinum complexes.[Lo~
generally gave only low to moderate enantiomeric excesses.
We now report a new method for the enantioselective epoxidation of x,B-unsaturated ketones 1 with Oz in the presence of
Et,Zn["] and (R,R)-N-methylpseudoephedrine to afford the
chiral @epoxyketones ( R , S ) - 2 (Scheme 1). The epoxidation
proceeds with excellent yields (94-99%). virtually complete
diastereoselectivities ( d ~ > 9 9 % ) and
,
except for one case, with
high enantiomeric excesses ( c v = 61, 82-92%) (Table 1 ) . The
Table I z./l-Epoxyketones 2 pi-epared by diasterco- and rnitiiti~sele~tive
epoxidiitton o r ?./{-unsaturated kctonea 1
2
a
b
c
d
e
f
g
R'
R'
I
YItId I/(,
[Ill "!h] "%]
Me
3 96
3 YO
Er
,7Pr
3 99
3 97
iPr
16 94
Ph
1Bu
PhCH,CH, 41 99
2.4.6-Me,C,,HL EI
89 94
Ph
Ph
PI1
Ph
Ph
>'I9
w[;t]
[TIP
"X,]
((,.
x5
91
87
02
61
90
>99
>99
>99
>Y9
>99
>99 X I
to Fe"' occurs, which can be proved by the characteristic color
change upon treatment with K,[Fe(CN),] and KSCN.["] It is
likely that 4 is the species that actually epoxidizes the x,/f-unsaturated ketones asymmetrically. In the epoxidation process the
oxygen of the carbonyl function first coordinates the zinc atom
in 4, with concomitant attack of the ethylperoxy anion in /j-position to form the intermediate 5. This reaction constitutes a
Michael-type addition. The subsequent cyclization gives the
epoxyketone 2 and 6.["1 In this way. rran-epoxides are exclusively formed from (E)-x,/j-unsaturated ketones (de > 99
Since the reaction rate strongly decreases upon introduction of
voluminous groups adjacent to the carbonyl function (see 2f.
2g). the formation of 5 is probably the rate-determining step.
Upon hydrolysis of 6 the chiral amino alcohol is formed, which
can be virtually quantitatively recovered with unchanged enantioineric purity (Scheme 2).
Et2Zn + R'OH
Conl'. [h]
CH>CI2J ir./$)
EtZnOR* +
0 2
-
EtZnOR* + C2H6
3
EtOOZnOR*
4
c0.4 (1.2)
+13.8(14)
+i).9(I,lJ
+370(1.3)
-13(1(1 I J
-50 I ( 1 . 2 )
+?0Y ( 1 1 )
[a] Determined b! NMR-hhift experiments with [Eu(trc),~]( t k = 3-iti-illuoromethylh~dron~iiir~li~lent')-~/-caniphorltre)
[h] Derived troni 2e buxxi on the it\sumption o f a unforin 1-e;ictjon niccliants~ii.[c] Determined h) comparison 01' the
oplical rotation w i t h literature data 11 31
R'
-
R'
R
5
2
+ R*OZnOEt
6
Scheme 2 P r ~ p ~ m~ ~l~ L C I I O I Iti~ccliiims~iirhr the i ~ s ~ m m e t r iepoxidation
c
or
ellollcs.
chiral alcohol (R,R)-N-methylpseudoephedrine employed is
readily accessible from cheap (R,R)-pseudoephedrine by methylation["l and can be virtually quantitatively recovered after the
reaction by a simple chromatographic elution (Scheme 1 ).
02,Et2Zn, R*OH
toluene, 0°C
94 - 99%
0
II
R"
Y
1
NMe,
Scheme 1 Ashmniett-ic epoxidarton olenone, w i t h 0, i n the pi-crence oi'Ft,Zn m d
~~-methylpseudoephedi-tne.
The epoxidation, which is carried out as a "one-pot" reaction
probably proceeds as follows:[141Firstly. ethyl zinc alkoxide 3 is
formed from diethylzinc and the chiral aIcohol.[lslThe expected
evolution o f a gas (ethane) was observed. The substitution of the
second ethyl group by an alkoxy ligand is very slow. Therefore,
insertion of O2into the Zn -C bond between the remaining ethyl
hgand and the zinc atom is preferred.["' In the course of this
process the chirally modified alkoxy(ethy1peroxy)zinc 4 is
formed. The measurement of the absorption of oxygen by a
solution of 3 in toluene at room temperature gave a value of
25.8 mL (1.06 mmol). According to the Van der Waals equation
absorption of 26.9 mL 0, was expected for 1.1 inmol 3. After
removal of the solvent in vacuo, 4 remained as a colorless powder. Upon addition of 4 to an aqueous Fe" solution, oxidation
The substituents R' in /$position have only a slight influence
on the enantioselectivity. Only the phenyl group leads to a significant decrease in the enantiomeric excess (see 2e). In the
scope of this work 35 chiral alcohols such as (Sf-l-phenylethanol. (R,R)-N-ethylpseudoephedrine. ( - )-menthol, ( - )8-phenylmenthol, (S)-2,3-dimethyl-1.3-dioxolan-4-methanol,
a s well as nine solvents were tested in the asymmetric epoxidation of enones. (R.R)-N-Methylpseudoephedrine and toluene
proved to be best suited. The stereochemical result (that is. the
tr.cir7.s-(R.S)configuration of the epoxyketones 2) can be explained by means of the transition states A or B with R or S
configuration at the zinc atom. respectively. which are depicted
in Figure 1. In this picturc the chiral alkoxy(ethy1peroxy)zinc4
attacks the .xi face of the s-cis conformation of the ( E )enones in
the fashion of a n oxa-Michael addition. Transition state A
shows particularly well that the steric hindrance between R ' and
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the phenyl Sroup as well as the interaction between R2 and the
dimethylamino group, which are caused by a rotation of the
enone plane by 180 ', significantly impedes the attack at the re
face of the enone.
The zinc his-alkoxide 7 was obtained by the reaction of two
equivalents of (R,R)-N-methylpseudoephedrine with diethylzinc in pentane (Scheme 3). However, 7 does not react with the
enones 1 under standard conditions. As can be seen from Figure 2. the zinc bis-alkoxide 7 exists as a dimer in the solid
pentane, RT
2Et2Zn + 4R*OH
+ 0°C + -25°C
T
M
e
-
[Zn(oR*),ln
7
R*OH: Ph
NMe2
Scheme 3. Preparation of the chiral zinc his-alkoxide 7. R T
=
room temperature
n
Fig. 2. Structure oftlie enantiomerically pure zinc his-alkoxide 7 in the solid state
(SCHAKAL plot)
state[20Jin which the zinc atoms are surrounded by three oxygen
and two nitrogen atoms each to form a distorted trigonal
bipyramid (coordination number 5).[Z11The structure is C,-symmetrical and is, to the best of our knowledge, the first crystal
structure of a chiral zinc bis-aminoalkoxide.
This new method for the zinc-mediated asymmetric epoxidation of r,P-unsaturated ketones opens an efficient diastereo- and
enantioselective access to trans-configured r,B-epoxyketones.
The use of the cheap chemicals 0 , and Et2Zn as well as the
possibility of recovering the employed chiral additive quantitatively makes this method interesting also in terms of industrial
applications. Further work on the optimization of the method
and extension to other electron-deficient alkenes is underway,12zl
E.\-peviriierltnl Procediire
Asymmetric cpoxid;ition of x/j-unsaturated ketones 1 : A solution ofdlethylzinc in
dded to a stirred solution of ( I R.2R)-N-methylpseutoIueIlc ( I 0 mL. I I M j
doephedrine ( [ 3 ] . 2.4 minol) i n dried toluene (10 mL) i n a 50 mL Schlenk flask
under ail 'irgon atniobphere at 0 C After 80 inin a slight 0, pressure was applied
from a hnlloon filled with 0 , so that the argon inside the flask was not removed.
After stirring for 2 5 h the reiiction mixture was cooled to - 78 C and z./j-unsatui-,ited ketone I ( I i i i i i i o l in 1 mL dried toluene) was added. The reactioii mixture was
srirred for 30 inin ;it thi, temperature and then rapidly warmed up to 0 C (ice water
bdth) undcr comtdiit stii-ring1241. At the end o f the reaction (TLC control), aqueoub
phosphatc hiifler \(ilu~ion(8 mL. pH 7) was added. After the separation of the
layers mid extraction of the aqueous layer with dichloromethane. the combined
oi-ganicla>ei-\werc dried over Na,SO, and concentrated. After purification by flash
chromatography (cthcr petroleum ether 1 24 to 1'4) the z,/j-epoxyketones 2 were
obtained ['S]. (R.R)~,V-Methylpseudoephedrinecould he recovered virtually quanh iinchnnged enantiomeric purity from the same chromatographic
titativel? ~ i t :in
column with ;I poloi- eluent (methano1,ether 1 9, mixed with 1 vol% isopropylamincJ
Received. March 18, 1996 [Z89341E]
German version: Angcii.. Climii 1996. /08. 1827 - 1829
Keywords: asymmetric epoxidation - chirai auxiliaries
* epoxyketones
zinc compounds
. enones
1
K Katsuki. K. B. Sharpless. J A i n C%Piii.Soc. 1980. /(I?. 5974 .5976.
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.S?vt/iesi.$ (Ed.: 1.
Ojima). VCH. New York. 1993. p. 103: c) 4.C Oehlschlager i n Hoiiheii-W(,v/,
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Sn/ / i ~ s i $(Ed.:
.
I . Ojlma). VCH. New York. 1993. p. 159.
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1984. 41). 5207 521 I . cl
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Climi. 1990. 5s. 6047-6049. e) P. W. Baiires. D. S. Egglcston. J R. Flisak. K.
Gombatz. I Lantos. W. Mendelson. J. J. Remich. E , t r ( i / i d o i i LFir 1990. 31.
6501 - 6504: f) C. Bolm. Angcw Ciirni. 1991. 103. 414 415: Airg(.c.ii..Ch(vii. h i ! .
C / .G i g / 1991. 30. 403-404. -9) J. R. Flisak. K. J. Gombatz. M M Holmes.
A. A Jarmas. I. Lantos. W. L. Mendelson. V. J. Novack. J J. Remich. L
Snyder, J 0,x C/imi. 1993. .i8, 6247-6254. h) M. E. Labterra Sancliei. S. M.
.
PerAi/i T~iiii.\ / 1995. 1467 . 1468. I ) M. E. Lasterra
Roberts. J C h ~ i iSoc
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[7] Benzylquininium chloride: a ) R. Helder. J. C Huminelen. R W P. M. Lame.
J. S. Wiering. H Wynherg. 7i./riihei/roriLrti. 1976. 1831 1834: bl J. C Hummelen. H Wynherg. ihirl. 1978, 1089 -1092: c ) H. Wynberg. B. Marsman.
J 0,x Chwi. 1980. 45. 158- 161 : d ) H Pluiiii. H. Wynhcrg. hid. 1980, 45.
2498 -2502: e ) Y Harigaya. H.Yamaguchi. M. Onda. Hi.ti,roci.</v\ 1981. 15.
183- 185.
(81 Bovine serum albumin: a ) S. Colonna. A. Manfredi. ~ / r ~ ~ / l ~ ~Lc*f/
l / r ~1986,
J i i
27. 387-390; h) S. Colonna. A. Manfredi. A. M Spadoni. ihrd 1987. 78.
1577- 1580. c) S. Colonna, N. Gaggero, A Manfredi. A. %I Spndoni. L. Casella. G Carrea. P. Pasta. Ewrihedroii 1988. 44. 5169 517X.
[9] Cyclodextrins: a ) S. Banfi. S. Colonna. S Julia. Si.i?//r.( O ! i i i i n o i 1983, 13.
1049- 1052. h) S. Colonna. S. Banfi. A. Pagagni. GKZ. C h i i n l i d 1985, 115.
81 - 83: c ) Y. Hu. A. Harada. S. Takahashi. S)ii//r. Coiiii1iiiti. 1988. I S . 1607 1610; d ) S. Colonna. A Manfredi. R. Annunziata. N. Gagpero. J 0i.y Chri?i.
1990. 55. 5862-5866
[lo] Chiral platinum complexes: C Baccin, A. Gusso. F. Pinna. G Strukul.
O~~~o/ioiiii~/u/lic.\
1995. 14. 1161 1167.
[ I l l Diastereosclective epoxjdation or enones with the system O? R,Zn have already been reported. K Yamamoto. N Yamamoto. C/i?iii. Lcrt. 1989. 1149
1152. The authors postulated ROOZnR as the oxidinng specie\. However. our
asymmetric variant supports the reaction mechanism depicted i n Scheme 1 via
4. Cyclohexenone is not epoxidized under our conditions
[IZ] Prepared according to a ) S. Smith. J C%ori Soc. 1927. 2050 2059 ( 6 5 % yield.
m.p. 29 C. b.p. 91 -92 C ( 8 mbar). [z]/' = - 48.6 (c, = 5 1 i n MeOH)). in
agreement with literature data: b) W N. NaSai. S. Kanao. Jii\rir.s Lwhi~.\A m .
C/iw?. 1929. 470, I57 - 182: c ) T. Kanzawa. Eli//. C/i(wi. S J C
J p. i . 1956. 7Y.
398 403: d ) K Yamamoto. K. Tsuruoka. J. Tsuji, C/iwi Lrrt. 1977. 11 151 1 16. ej H -J. Schneider. M Lonsdorfer. @< M q t i . RNJK 1981. (6121.
133- 137.
113) B. Marsman. H. Wynherg. J. 0,:q U i w i . 1979. 44. 2 3 1 1 ~2314
[14] The zinc complexes depicted in the formulas are presented iis monomers for the
sake of simplicity. They d o not account for the fact thiit these species could
possibly exist as dimers.
[I51 Alkyl zinc alkorides Here successfully employed in the rn,iiitIoselectivc addition of dialkylzinc to aldehydes. Reviews- a ) R. Noyori. M Kitiiinura. .4ngOil
C/ii,m. 1991. 103. 34 -55. Ang<,ii'. ChiVJl. / f i t Ed En,</. 1991. 30. 49 -69: h) K.
Soai, S. Niwa, C/iriii. Rev. 1992. Y7. 833 -856
[I61 G. Sosnovsky. J. H. Brown. Clieiii. Rev. 1966. 66. 529--566
iriid /)rii/xirutiwi L I I I O ~ : ~ N I I ~ [17] G. Jander. E Blasius. Lrhrhiidi cler ~mu/i~/i.w/wii
.s(./icwClieiJiii,. 14th ed.. Hinel. Stuttgart. 1995. p 422
1181 An analogous mechanism was postulated for the epoxidation olenones with
H , 0 2 i n alkalinc medium H. 0. House. R. S. Ro. J. ,4111 Ciiviii. So<c 1958. KO.
2428 2433.
1191 The couplin_r constants o f t h e vicinal protons i n m i i i \ positioiih zit the oxirane
ring of the epoxyketones 2 are 1.68 1-02 Hz ( ' H NMR spectrum).They are iii
accord with the literature data for t1'0r15 epoxides: C A Rc-illy. J D Swalen.
J. C/wiii Plij-s. 1960.32. 1378-1384: b ) K . L. Williamson.C. A. Lanford.C. R
Nicholson. J. .4rir C/iiwi. Siic. 1964. 86. 761-765.
~
COMMUNICATIONS
[20] X-ray crystal analysis of 7 : monoclinic, space group P2,(4), u = 13.988(2).
h = 18.846(17), c = 14.141(9) pm, [j = 106.09(2)-; 25 reflections, 12.23 ' < ( I <
1 6 . 9 8 . , Z = 2 . V=35818~',M,=1202.29.y,,,,,=l.l15gcrn~'.Thecrystal was measured directly without capillary in a stream of cold nitrogen
( T = 190 K), F(000) = 1288, Mo,, radiation ( h = 0.71069 A), sfnO/imax=
0 651, p = 7.32 c m - ' (no absorption correction), R,,,, = 0.102(30), 4963 observed reflections (1>2a(I)) in the range - 1 8 i h < 1 7 , O < k < 2 4 , 0</<18.
The structure was solved by the heavy atom method (SHELXS86 [26]), refinement with XTAL3.2 [27]. 4963 reflections in final least-squares full-matrix
refinement of410parameters. R = 0.103, R, = 0.077 (\I. = ljrr') S = 2.717,
residual electron density 1.6 e A 3 . Compound 7 crystallizes with two free
molecules of the ligand (disordered) per molecular unit. The poor quality of the
crystals allowed only the anisotropic refinement of the Zn atoms and of their
immediate etivirotiment (OIA-D. NIA-D. CIA-D. CZA-D). All other
atomic parameters were refined isotropically. The positions of the hydrogen
atoms were calculated All attempts to prepare crystals of superior quality were
unsuccessful. The crystallographic data (without structure factors) of the structure described in this publication were deposited as "supplementary publication no. CCDC-I 79-57" at the Cambridge Crystallographic Data Centre.
Copies of the data can be ordered free of charge from the following address:
The Director, CCDC. 12 Union Road. GB-Cambridge CB2 IEZ(fax: Int. code
+ (1223) 336-033; e-mail: techedto chemcry.cam ac.uk)
[21] A related achiral zinc bis-alkoxide structure with C, symmetry is known: P. L.
Orioli, M Di Vaira, L. Sacconi. Inoug. C/imni. 1966. 8. 400 -405.
[22] We have already succeeded in epoxidizing a nitro alkene diastereo- and enantioselectively by the same method: J. Zhu. Dissertation, Technische Hochschule
Aachen, 1996.
[23] The epoxidation carried out with half the amount of (IR.2R)-N-methylpseudoephedrine gave Compardbk yields at longer the reaction times. However. the
enantiomeric excesses fell by several percent in most cases (example 4b: 17 h.
94% yield, 8 7 % ee).
[24] Since extensive exposure to 0, can have an adverse influence on the reaction.
it is recommended to replace the oxygen balloon with an argon balloon after
3.5 h
[25] In addition. 2g was prepared by preparative HPLC. All new compounds gave
consistent spectroscopic data (IR, NMR, MS) and correct elemental analysis
or high-resolution mass spectra.
[26] G. M. Sheldrick in CrwuNogruphi~Conipuring C (Eds.: G. M. Sheldrick. C.
Kruger, R. Goddard), University Press. 1985, p. 175.
[27] S. R. Hall, H. D. Flack, J. M. Stewart, XTAL3.2 Re/erenw M o n u d Untversities of West Australia, Geneva, and Maryland, Lamb, Perth 1992.
reaction proceeds analogous to that of C0,-should
lead to the
formation of sodium nitridonitrate.
At a temperature between 300 and 400 "C,Na,O does indeed
take up an equimolar amount of N,O. According to the X-ray
powder diagrams the reaction goes to completion (no Na,O
reflections were detected), and the elemental analysis confirms
the expected composition Na,N,O, .I3] The colorless, extremely
moisture-sensitive product is obtained as microcrystals. It is
thermally stable up to 325 "C; above this temperature quantitative disproportionation occurs with N, cleavage and formation
of "sodium orthonitrite" [Eq. (a)].[41
3 Na,N,O,
-
2Na,O(NO,)
+ 2 N,
Neither by annealing (due to the low decomposition temperature) nor by recrystallization (due to the insolubility in aprotic
solvents and the decomposition in protic solvents) was it possible to obtain single crystals of Na,N,O, . The proof of its constitution was therefore undertaken by a crystal structure determination from X-ray powder data without using any a priori
knowledge[s1 and confirmed spectroscopically (lSN MASN M R , vibrational spectroscopy).
According to the results of the X-ray structure analysis
(Fig. l),I6] the product of the reaction of N,O with Na,O is
cis-Sodium Hyponitrite-A New Preparative
Route and a Crystal Structure Analysis**
Claus Feldmann and Martin Jansen*
Dedicated to Professor Hans Georg van Schnering
on the occasion of his 65th birthday
The family of triatomic molecular 16-electron species has attained an impressive size. Previous studies on these molecules o r
molecular ions have concentrated on their preparation and
structural and spectroscopic characterization."] Their electronic
structures correspond to a large extent and should, as a result,
lead to similar chemical behavior-an aspect that has previously
been given scant regard with respect to their use in synthesis.
The central atom, being generally positively polarized, should
function as a Lewis acid center. This behavior is well-known for
CO,, but otherwise only described for CS, .lZl Novel interesting
tetraatomic complex anions should be accessible by the addition
of oxide, nitride, or sulfide ions, for example. To test this idea we
studied the effect of laughing gas (N,O) on Na,O, which-if the
[*I
Prof. Dr. M. Jansen
Institut fur Anorganische Chemie der Universitat
Gerhard-Domagk-Strasse I. D-53121 Bonn (Germany)
Fax. Int. code + (228)735660
Dr. C Feldmann
Max-Planck-lnstitut fur Festkorperforschung, Stuttgart (Germany)
[**] This work was supported by the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen Industrie.
(a)
10.0
26.0
42.0
20
-
58.0
74.0
Fig. 1 Profile fitting for ci.r-Na,N,O,. Top: measured intensities; bottom: difference.
unexpectedly cis-Na,N,O,, the constitution of which was thus
unequivocally confirmed for the first time. The bond lengths of
the cis-hyponitrite ion of 1.20(3) (N 1 -N2), 1.40(3) (N 1 - 0 l),
and 1.39(3) 8, (N 2 - 0 2) correspond approximately to those of
a N - N double bond (1.1 5 A) and two N -0 single bonds
(1.408,).['1 The bond angles of 119.8(4) ( 0 1 - N l - N 2 ) and
119.2(4) ' ( 0 2 - N 2 - N l ) a g r e e w i t h thoseexpectedforapseud o trigonal-planar arrangement.['] With a dihedral angle
( 0 1 - N 1 - N 2 - 0 2 ) of0.6(3)", cis-N,O:- is, within the limits
of error, planar. The anion has C , site symmetry; the measured
deviations from the highest possible symmetry (point group C2J
lie within the standard deviations, however.
The "N MAS-NMR spectrum of cis-Na,'sN,O, (99 YO"N)
has. in addition to the rotational side bands, just one isotropic
signal (6 = 364(1)). At a line width of A6 = 2.0(5), the nitrogen
atoms can be considered as chemically equivalent, which would
agree with the point groups C,, or C , for cis-N,O:-. The vibrational spectra show a clear splitting of all significant peaks,
which in accordance with a point or factor group analysis is to
be expected (Table 1). Interestingly in this case, the vibrational
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presence, asymmetric, diethylzinc, enones, epoxidation, oxygen, methylpseudoephedrine
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