Chemo- and Diastereoselective Epoxidation of Chiral Allylic Alcohols with the Urea Hydrogen Peroxide Adduct Catalyzed by Titanium Silicate 1.код для вставкиСкачать
COMMUNICATIONS  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.  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.  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. + 0570-0833:9~~350H-0~80 $ 15.00 .25/0 Angebr. Clrrm. Int. Ed. Engl. 1996. 35. No. 8 COMMUNlCATlONS 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 , 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 : 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. , 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). COMMUNICATIONS 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.  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.  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.  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.  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. .