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Chemo- and Diastereoselective Epoxidation of Chiral Allylic Alcohols with the Urea Hydrogen Peroxide Adduct Catalyzed by Titanium Silicate 1.

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[3] C:C.
Su. .I.-T Chen. G:H. Lee. Y Wmg, J. A m . Clwrn. Soc. 1994, 116, 49995000; J. Tsuji, H . Watanabe. 1. Minami, I. Shimizu, ihid. 1985. 107, 2196-2198.
(51 All tlir products listed in Table 1 were properly characterized by spectroscopic
methods (IR, 400 MHz 'H NMR, high-resolution MS) and elemental analyses.
[6] Ketones seem to react equally well. For example. the reaction of l b (X = OBz)
with acetophenone under the same conditions as that of run 2 in Table 1 (THF,
29 h) provided 3-methyl-2-phenyl-4-pentyn-2-ol in 58% yield.
[7] The complexes of I11 and IV with M = ZnEt and ZnEt; may be generated via
a similar transition state to that proposed for an ally1 group migration of mallylpalladium t o ZnZt Ira].
181 E. J. Corey. K. A. Cimprich, J A m . Clien?. Soc 1994, 116. 3151-3152; J. A.
Marshall, .I.Perhins. J Org. Cliem. 1994. 59, 3509-351 1 : H. Yamamoto in
C'omprrhensivc, Orgcriiic Svithesis, K)/. 2 (Eds.: B. M. Trost. I Fleming, C. H.
Heathcock). Pergdmon. Oxford, 1991, pp. 81 -98
191 I11 with M = ZnCl provides utiri-2 with high selectivity: G. Zweifel, G. Hahn.
J. Org. Chem. 1984,49,4565-4567.
56
1
:
I
14
30
OH
R
threo-2
Chemo- and Diastereoselective Epoxidation of
Chiral Allylic Alcohols with the Urea Hydrogen
Peroxide Adduct, Catalyzed by
Titanium Silicate 1**
Waldemar Adam,* Rajiv Kumar, T. Indrasena Reddy,
and Michael Renz
Titanium silicates belong to the class of heterogeneous oxidation catalysts that oxidize a variety of organic compounds with
aqueous hydrogen peroxide as relatively cheap oxygen source.
Titanium silicate 1 (TS-l), the titanium analog of the ZSM-5
zeolite, can be recycled many times without losing its activity
and catalyzes C H insertions,"] epoxidations,['l and arenei3l and
heteroatom oxidations of aminesf4]and sulfides.[51
The high reactivity of the catalyst can also be a disadvantage,
for example, in the product selectivity of epoxidations. For amethylstyrene only 1 5 % of the epoxide is obtained; the rest
undergoes further reactions like epoxide opening and rearrangements.[@An important aim is the control of diastereoselectivity.
In spite of the many investigations in this research field, only
little has been reported. Tatsumi et al.[2d1describe the epoxidation of some chiral allylic alcohols, but neglect to comment on
the diastereoselectivity. The only known examples are the
diastereoselective epoxidation of two cyclic allylic alcohols.[71
In continuation of our studies on selective catalytic oxyfuntionalizations of organic substrates,[*]we report herein the first
diastereoselective epoxidations of acyclic systems and compare
their efficiency and diastereoselectivities with relevant known
methods. The epoxy alcohols of defined configuration are useful
building blocks for oxyfunctionalized natural product^.'^]
When, as usually practiced, dilute, aqueous hydrogen peroxide solution is used, migration and/or substitution of the hydroxy group was observed (Scheme 1, path a). These undesirable reactions most likely derive from allyl-stabilized cationic
intermediates.['" If 85 % H,O, is employed in the presence of
MgSO,, or if it is filtered over this salt prior to use. the desired
epoxide 2f was obtained in 85 % yield (Scheme 1, path b). Thus,
[*] Prof. Dr. W. Adam. Dr T. 1. Reddy, DipLChem. M. Renz
lnstitut fur Organische Chemie der Universitht
Am Hubland, D-97074 Wurzburg (Germany)
Fax: Int. code +(931)888-4756
e-mail: adam((<chemie.uni-wuerzburg.de
[**I
880
Dr. R. Kumar
CdVdlySlS Division, Nationdl Chemical Laboratory. 41 1008 PUne (India)
This research was supported by the Deutsche Forschungsgemeinschaft (SFB
347: "Selektive Reahtionen Metall-aktivierter Molehule") and the Fonds der
Chemischen Industrie.
VCH Verlagsgesellscllufr nihH, 0-69451 Weinhrirn. I996
erythro-2
Scheme 1. Heterogeneous TS-1- and homogeneous Ti(OiPr),-catalyzed epoxidationsoftheallylic alcohols 1 and side reactions for TS-I. a) For If TS-1(100 wt%).
H,O, (30%). H,O. 50 'C, 3 h, conversion>95%. m . b . s 5 0 % . m.b. = m a s s balance. b) For If: TS-l (100 wt%), H,O, (85%). MgSO,, acetone. reflux. 20 h.
conversion 90%. yieId>95%. c) TS-1 ( 5 0 % ) . UHP (I equiv), acetone, 5 0 T . 1420 h, conversion>95%. yield 76-97%. m.b. >76%. d) Ti(OiPr),. /BuOOH
(1 Zequiv). CH,CI,. 16 h, conversion > 8 5 % . yield 82-9546. m.b. 2 8 0 % .
whereas the presence of water usually makes no difference in
epoxidations because TS-1 is known to be hydrophobic, in the
case of the allylic alcohols it causes undesirable side reactions.
The potentially explosive concentrated hydrogen peroxide can
be replaced by the easier to handle and safer, anhydrous crystalline urea adduct of hydrogen peroxide (urea hydrogen peroxide, UHP). The epoxy alcohols were obtained in similarly high
yields and high product selectivity (Scheme 1, path c). Only
traces of the C-H insertion product, namely the ketone, were
detected, and in no case d o the above-mentioned troublesome
side reactions occur. The allylic alcohols 1 were consumed completely in 12 to 24 h to form the epoxy alcohols 2, which were
isolated in 72 to 95% yields.
To compare the diastereoselectivities of the heterogeneous
TS-1 zeolite with those of a homogeneous titanium catalyst in
solution, we chose the tBuOOH (TBHP) and Ti(OiPr), oxidation system (Sharpless epoxidation without tartrate; Scheme 1 ,
path d). The diastereoselectivities of the oxidants UHP/TS-l
and TBHP/Ti(OiPr),, and for comparison also meta-chloroperbenzoic acid (m-CPBA) and TBHP/VO(acac),, are shown in
Table 1.
With the UHP/TS-1 oxidant, substrate-specific selectivities
are obtained when 1,3-allylic strain (caused by the substituents
R 3 and R4)is present in the substrate. For the allylic alcohol If,
for example, the tlireo isomer was obtained essentially exclusively (entry 6, Table I), while the alcohols Id and l h also show
relatively high threo selectivity (entries 4 and 8 ) . Substrates with
R' and R3 substituents, for example l e and lg, still give high
rhreo selectivities (entries 5 and 7), which indicates that the R'
substituent exercises no significant influence on the diastereoselectivity. The allylic alcohol l b exhibits no diastereoselectivity
(entry 2). like substrates without R' and R3 substituents (la and
lc, entries 1 and 3).
The substrate If shows a high threo selectivity with the oxidant rn-CPBA (entry 6). In this case, the coordination of the
substrate to the peracid through hydrogen bonding is optimal
for oxygen transfer when the dihedral angle (0-C-C=C) of
the allylic alcohol is 120" (see structure E, Fig. l).[''' The two
possible diastereomeric transition states are then energetically
sufficiently differentiated by 1,3-allylic strain so that one
predominates and one epoxide diastereomer results preferentially.
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Table 1 . C'ompai-iaon of the diastereomeric ratios ( d x ) for the epoxidations of the
allylic alcohols 1 bith the UHP'TS-I. TBHPiTi(OiPr),. n-chloroperbenzoic acid
(rwCPBA) and TBHP,'VO(acac), oxidants. Hacac = acetylacetone
E:ntry
UHP
1's-1
Acetone [a]
d.r. [d]
OH
?H
6
TBHP;
Ti(OiPr),.
CH,CI, [b]
d.r. [d]
rir-CPBA.
CH,CI,
d.r. [el
TBHP.
VO(acac),,
C,H, [cl
d.r. [el
71:29
60:40
20-80
la
65.35
Ib
50:50
22:78
45.55
5.95
Ic
65.35
66: 34
64:36
29:71
Id
X0:20
91 : 9
95:5
71 2Y
le
81.19
83:17
90: 10
33:bl
f
If
Y5:S
95:5
95:5
86:14
$:
Ig
Y0:lO
Y5:5
90: 10
lh
80:20
Y5:5
90:10
OH
2
3
5
)x
J
\
6
7
X
zu
C
Scheme 2. Catalytic cycle and structures of the titanium peroxide intermediates A
and Band ofthetransition stateC fortheoxygen transfer of the IJHPjTS-1 oxidant.
[fl
78:22
[a] The TS-1 was s)ntliesized by the published procedure with a Si:Ti ratio of about
19 [15], t h d is. 50 w t % TS-I represent 2.5 mol% based on the allylic alcohol; all
reactions here monitored by TLC to more than 95% conversion; after 12-24 h the
oxiranernethanols were isolated in 72-05% yields: traces of the enones were
detected in the ' H NMR spectra of the crude reaction mixture. [b] Carried out
by a modified procedure [16]: Ti(OiPr), was used in stoichiometric amounts.
[c] VO(acacj, was used in a catalytic amount (0.5 mol?'~) [d] Diastereomeric ratios
(ti r.) of/hrro er:i,l/rro products determined by ' H N M R analysis of the characteristic signal> in [lie crude rcaction mixture: error & 5 % of the stated values. [el Substrates l a d.f. sec ircf. [17], substrate le ref. [ I l l : [f] CDCI, as solvent.
D
E
Fig. 1. Transition states for the epoxidations with the oxidants I BuOOH,Ti(OiPr),
or tBuOOHWO(acac), (0)and ni-CPBA (Ej.
On the basis of solvent and acid/base effects on the reaction
kinetics, the active species for the TS-1 epoxidation is postuiated
to be similar to peracids (A, Scheme 2)IZc, 1 3 ] and not to the
titanium peroxo complex (B, Scheme 2). Consequently, hydrogen bonding between the oxidant and the substrate also operates for the TS-1 epoxidations, and the oxygen is transfered at
an optimal dihedral angle of 120' in the allylic alcohol (C,
Scheme 2). This analogy to the transition state for the oxygen
transfer of m-CPBA rationalizes the observed identical selectivities; however. the advantage of the UHP/TS-l oxidant over
ni-CPBA is its catalytic nature (Scheme 2) and the H,O, oxygen
source.
As with III-CPBA, 1,2-allylic strain is ineffective, as illustrated
by substrate Ib. for which no e r J h v selectivity was obtained
with either oxidant (entry 2, Fable 1). Erythro selectivity would
be expected if the dihedral angle were 40", as it is in the epoxidations of allylic alcohols by the TBHP/VO(acac), oxidant (D,
Fig. 1 ) . [ I 4 l The stereochemical probe with both 1 2 - and 1.3allylic strain, namely the alcohol le, which for the vanadium
oxidant gives preferentially the erytliro diastereomer, confirms
the similarity between the m-CPBA and UHPITS-1 oxidants in
view of the pronounced threw selectivity (entries 5 and 7).
Only the substrates Id and Ih (entries 4 and 8), which do not
possess frcrns substituents. deviate from this trend. Whereas in
the case of IwCPBA the threo epoxy alcohols are obtained due
to the 1,3-allylic strain. the diastereoselectivity for the heterogeneous Ti system drops significantly- -surely a zeolite framework
effect. We propose that the majority ofthe inolecules will usually
react through transition state C; however. for cis olefins, the
sterically less hindered side of the double bond allows additional, less selective attack on the oxygen atom to be transfered in
the activated complex. Such unselective possibilities are presumably prevented by steric interactions of the R Z or R 3 substituents with the zeolite lattice. Alternatively, it is also possible
that the less stereoselective Ti peroxo complex B is involved in
the oxygen transfer, a pathway that is less likely for more sterically hindered substrates such as I f and l g (entries 6 and 7).
The heterogeneous UHP/TS-1 oxidant differs from the homogeneous TBHP/Ti(OiPr), system in several points. A necessary condition for stereocontrolled oxygen transfer in the homogeneous system is coordination of the allylic alcohol to the metal
center by means of an alcoholate bond, as suggested by the fact
that unfunctionalized olefins are only slowly oxidized and in
poor stereoselectivity. Furthermore, the dihedral angle for the
TBHP/Ti(OiPr), system has to be smaller than 120 because, in
contrast to the UHP/TS-1 system, 1.2-allylic strain causes significant erJ,throselectivity (entry 2), but it must be larger than
the 40" for the TBHP/VO(acac), oxidant because for the stereochemical probe with both 1,2- and 1,3-allylic strain, the latter
dominates (entries 5 and 7). Surprisingly. in contrast to the
vanadium oxidant, the homogeneous titanium oxidant is very
sensitive to 1.3-allylic strain and the fhreo epoxy alcohols are
obtained essentially exclusively (entries 4. 6. and 8).
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Thus, the heterogeneous UHP/TS-1 oxidant conforms mechanistically to m-CPBA, which would be expected in view of the
similar active species for the oxygen transfer (cf. transition states
C and E). Hydrogen bonding coupled with 1,3-allylic strain
provides the high threo diastereoselectivity. as exemplified in
substrate If, and I ,2-allylic strain has no significant effect (cf.
derivative lb). However. mechanistic similarities to the homogeneous TBHP/Ti(OiPr), oxidant are also evident. because the
latter also displays high fhreo selectivities. but it differs from the
UHP/TS-I oxidant for substrate Ib, for which TBHP/Ti(OiPr),
shows significant erytizl-oselectivity in view of the greater importance of 1.2-allylic strain. Moreover, besides these mechanistic
insights, it should be emphasized that the UHP/TS-1 oxidant is
an environmentally acceptable, safe, and mild oxidant for the
epoxidation of allylic alcohols. In this way, side reactions that
are observed with dilute, aqueous hydrogen peroxide are avoided, and the use of the potentially explosive, concentrated hydrogen peroxide is circumvented
[lo] a) A. 1. Biaglow. R. J. Gorte, D. White. J. Chmi. So?. Clirin. Cominun. 1993.
1164-1166. b) D. FPrcdSiu, ihid. 1994, 1801-1802; c) T. Xu, J. Zhang. E. J.
Munson. J. F. Haw. ihid 1994. 2733-2735: d j M. L. Cano. V. Fornes. H.
Garcia. M. A. Miranda. J. Perez-Prieto, i h i d 1995. 2477 -2478.
1111 C. B. Khouw, C. B. Dartt. J. A. Labinger. M. E. Davis, J (’utol. 1994, 14Y.
195-205
1121 a ) A . H. Hoveyda, D. A. Evans, G. C. Fu. Chrm. Rcw. 1993. 93. 1307- 1370; h)
W. Adam. B. Nestler. 7ictrahedroi?Le~r.1993. 34. 61 1-614.
[13] A. Corma. M. A. Camblor. P. Esteve. A. Martinez. J. Perer-Pariente. J Curd
1994. 145. 151 -158.
1141 K. B. Sharpless. T. R. Verhoeven. A/dridiiiii;cu Acru 1979. 12. 63-74.
[lS] A. Thangaraj. S. Sivasanker. J Ciienr. Sm.. C%twr.Cotnmcm. 1992. 123- 124.
[I61 T. Katsuki. K. B. Sharpless. J. Ain. Cliein. So<. 1980. 102, 5974-5976.
[ I 71 B. E. Rossitcr. T. R. Verhoeven. K. B. Sharpless. firrrihr,dron Lerr. 1979.47334736.
Experimental Procedure
William P. Freeman, T. Don Tilley,* Glenn P. A. Yap,
and Arnold L. Rheingold*
A solution of 200 mg (2 00 mmol) of the allylic alcohol If in 10 mL acetone was
added dropwise to a suspension of 184 mg (2.00 mmol) U H P and 100 mg (SO wt%)
TS-1 in 10 mL acetone at room temperature (about 20 C). The mixture was held at
reflux for 20 h. filtered at room temperature through a glass filter. the residue was
washed with acetone (2 x 10 mL), and the solvent was removed in a rotoevaporator
(35 C. 20Torr). The crude product was analyzed by N M R spectroscopy and the
rhreojrrj rhro diastereomeric ratio of the sole product was determined to be 95;s at
a conversion of 90%.
Received: October 9. 19Y5 [Z8455IE]
German version: Aiiguii.. Clicwi. 1996. I W . 944- 947
Keywords: asymmetric epoxidations . epoxidations . catalysis
zeolites
.
[ I ] a ) D . R. C. Huyhrechts. L. DeBruycker. P. A. Jacobs. Nururc 1990.345. 240
242. b) T. Tatsumi. M. Nakamura. S. Negishi. H. Tominaga. J. C h m Soc.
Chcwi. Coinmuri. 1990,476-477:c) M. R. Boccuti. K. M. Rao. A. Zecchina.G.
Leofanti, G . Petrini. Stirrl. Sur,f. Sri. Curd. 1988, 48. 133-144; d ) B. Notari,
ihid 1988. 60. 413-425: e) M G . Clerici. AppI. Curd. 1991. 68. 249-261
121 a ) T. Tatsumi. M. Nakamura. K. Yuasa. H. Tominaga. Chem. Lerr. 1990.
297-298, b) T. Tatsumi. M. Nakamura. H. Tominaga. ihid 1989, 419-420:
c) M. G. Clerici. P. Ingalhna, J Curd 1993, 140. 71-83; d) T Tatsumi. M.
Yako, M. Nakamura. Y. Yuhara. H. Tominaga. J Mol. Curul. 1993. 78, L41L4S;e) A. Bhaumik. R. Kumar. P. Ratnasamy. Stud. Surf. Sci. Curd. 1994.84.
I883 - 1888.
, Perego, B. Notari. SNAM Progetti S. p. A U S A 1983.
[3] a) M. ~ a r a m a s s oG.
4410501 [Chmi.Ahsrr. 1982. 96,37802~1;b) A . V. Ramaswamy. S. Sivasanker.
P. Ratnasamy, M;croipororrs Mawr. 1994, 3. 451 -458.
[4] a ) P. Roffia. M. Padovan, E. Moretti. G . De Alberti, Montedipe S. p. A EP-A
1987, 208311 [Cliem. Ahsrr. 1987. 106. 155944~1:b) P. Roffa, G . Leofanti. A.
Cesana, M. Mantegazza. M . Padovan. G. Petrini, S. Tonti. V. Gervasutti. R.
Varagnolo, Chini. Iizd. iMilun) 1990. 72.598-603; c) J. S. Reddy, P. A. Jacobs.
J C/im?.Soc. Perkin lrriii.\. 1 1993. 2665- 2666.
[S] R. S. Reddy, J. S. Reddy. R. Kumar. P . Kumar. J. Cheni. Sor. Clwni. Conrmun.
1992, 84-85.
161 J. S. Reddy. U . R. Khire, P. Ratnasamy. R. B. Mitra, J. C/u~ni.Sor.. Cheni.
Co~miiuii.1992, 1234- 1235.
[7] R. Kumar, G. C. G . Pais. B Pandey. P. Kumar. J Chcwi. Soc. Chmi. Cornmun.
1995. 1315.- 1316.
[XI a) W. Adam. B. Nestler. J. h i . C/uwi. Soc. 1992, 114. 6549 -6550; b) W. Adam,
B. Nestler, ihirl. 1993. 1fS. 7226-7231; c) W. Adam. B. Nestler. A n p i . . C/irm.
1993, 105. 767-769; A n p i ’ . C/ien?.h i / . E d EngI. 1993. 32, 733-735. d) W
Adam, M. Richter. Acc. Clreirr. Rtp.7. 1994. 27. 57-62: e ) W. Adam. K. Peters,
M. Renz. Aiigmi. Chein. 1994, 106, 1159 1161 . A i g r i i . Chciii. lnr. 6 1 . Engl.
1994. 33. 1107-1108: f ) W. Adam. C. M Mitchell, AnEcir. Cheiii. 1996. 108.
578 - 5x1 ; g) W. Adam. F. Prechtl. M. J. Richter. A. K. Smerz. f i ~ r r d i d r o i iLer/.
1993. 34. 8427-8430: h) W. Adam, F. Prechtl. M. J. Richter. A. K . Smerz.
iWruhrdron Lrrr. 1995. 36. 4991 -4994: i)W. Adam, A. K. Smerz. Trtrruhrdron
1995. 51. 13039%13044.
191 a ) P. A. Bartlett. Tefruh~f/roii1980. 36. 1-72; b) B. Meunier. Cheiii. Rei,. 1992.
92.1411 -1456;c)OrganicPeroxygen Chemistry(Ed.: W. A. Herrmann).(Top.
Curr. Cheni. 1993. 164); d ) P. Besse. H. Veschambre. Terruhwlron 1994, 50.
8x85 -8927. e) A. Pfenninger. Syiir/icsi.s 1986. XY--l16, f ) M. G. Finn. K . B.
Sharpless in A,symmerric Swrhe.m. C’ol. V (Ed : J. D. Morrison). Academic
Press. Orlando, FL. 1985.
Silolyl Anions and Silole Dianions: Structure of
[K([1S]crown-6)+],[C4Me4Si2
-I**
Silolyl anions [C,R,SiR’]- have been the focus of recent experimentalr’-*] and theoreticalL3. 41 investigations. These studies
are concerned with characterizing the structural and chemical
properties of these novel x-electron systems, which may possess
some degree of aromaticity. Theoretical studies suggest a significant amount of delocalization for the free C,H,SiH- anion,
and N M R data obtained by Hong and Boudjouk for the lithium
and sodium derivatives of [Ph,C,Si(tBu)]- in T H F indicate
some delocalization of the negative charge in the ring.[’] We
have recently reported the metal x-complex ($-C,Me,)Ru[$C,Me,SiSi(SiMe,),], which appears to have significantly delocalized electron density in the C,Si ring, as shown by N M R
spectrosc~py.[~]
After the initial report by Joo and co-workers on the generation of the silole dianion C,Ph,Si2-, a number of investigations
described further properties for such species and their usefulness
as intermediates in the synthesis of silole derivatives.[61Based on
somewhat downfield-shifted 29Si N M R resonances, these species appear to have at least some delocalization of negative
charge in the five-membered ring.[6b,C1
The dilithium derivative
[Li(thf),][Li(thf),][~5,~1-C,Ph,Si],
recently described by West
and co-workers, appears to have a delocalized structure based
on the equivalent C-C distances in the C,Si ring.[6d1Calculations support this view,[6d*’I and Schleyer et al. have predicted
that the “free” silole dianion C,H,Si2- would be highly aromatic and form dilithium, disodium, and dipotassium salts with
the metals bound in an q5-fashion to both sides of the ring.17]
Here we report on a silole dianion of the latter type, which is
isoelectronic with tetramethylthiophene and has an aromatic
C,Me,Si2- ring.
Reduction of C,Me,SiBr,[81 with three equivalents of potassium in T H F gives a solution of dianion 1 (Scheme 1). as deter[*] Prof. Dr. T D. Tilley. W. P. Freeman
Department of Chemistry
University of California. Berkeley
Berkeley. CA 94720.1460 (USA)
Fax: Int. code +(510) 642-8940
Prof. Dr. A. L. Rheingold. G . P. A. Yap
Department of Chemistry
University of Delaware
Newark. D E 19716 (USA)
[**I This research was supported by the National Science Foundation. We thank
Greg Mitchell for helpful discussions. and Prof. P. von R. Schleyer for a
prepnnt of ref. [7].
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