BOOKS Contents H . Hopf ........................................... 1303 S. Hojjmunn .................................... 1303 Electrode Kinetics for Chemists, Chemical Engineers, and Materials Scientists . E. Gileadi W. Schmickler .................................. 1304 Dictionary of Trivial Names/Trivialnamen-Handbuch. Vols. 1-3 informationszentrum Chemie U. Eberhurdt ................................ 1305 W. Muder ......................................... 1306 Chemistry Imagined. Reflections on Science Unraveling DNA * R. Hoffmann, V. Torrence M. D. Frank-Kamenetskii * Scanning Electron Microscopy and X-Ray Analysis - R. E. Lee * Fach- Events 1208 Preview A-64 Author Index A 4 3 No Enantioselective Reactions in a Static Magnetic Field Based on part of the P h D thesis by G. Zadel (completed 1993) and parallel investigations by Catja Eisenbraun the communication “Enantioselective Reactions in a Static Magnetic Field” appeared under my auspices together with G . Zadel. C. Eisenbraun. and G . J. Wolff in this journal (Angcw. Chem. 1994, 106, 460; Angew. Chem. Int. Ed. Engl. 1994. 33. 454). Several independent research groups have informed me since that the experiments reported (1 ,Zaddition of Grignard compounds to aldehydes; reduction of prochiral ketones with lithium aluminum hydride), contrary to the results published by us gave no enantiomeric excesses. In light of this I instructed three experienced co-workers from my research group (F. Keller, K. Berlin, and T. Marx) in the absence of G. Zadel, and could detect no measureable enantiomeric excesses (NMR with [Eu(hfc),], G C with c(-cyclodextrin, polarimetry). In one case, we were able to prove quite clearly (GC-MS, polarimetry) that the starting solution prepared by G . Zadel for the reduction of propiophenone with lithium aluminum hydride also contained considerable amounts of ( +)-I -phenylpropanol in addition to propiophenone. G. Zadel admitted this deception and two other manipulations in front of witnesses. Therefore we must assume that the data in the publication as well as “successful” attempts at reproducing the results by other co-workers in my research group and guest scientists in the presence of G. Zadel came about because of consistent and particularly COMMUNICATIONS (51    191 [lo] data, conventional R [on F values for 2999 reflections with F,' P 2 0 ( F : ) ] = 0.0266. goodness of t i t on F 2 =1.199 for 272 parameters. Programs: SHELXTL:PC and SHELXL-93. Ci. M. Sheldrick. Universitit Gottinpen. Further details of the crystal structure investigation are avarlable on request from the Director of the Camhridge Crystallographic Data Centre, 1 2 Union Road. GB-Cambridge CB2lEZ (UK), on quoting the full journal citation. a) R. Strandherg. .4clu Chon. Scimd. SiJr.A 1973.27, 1004: b) W. Kwak, M. T. Pope. T. F. Scully. .I Ani. C/iiw/. Sot. 1975, Y7. 5735: c) J. K. Stalick. C . 0 Quicksall. / n o r E . Chein. 1976, 1.5, 1577: d ) D -G. Lyxell. R . Strandherg. Actu C F J , T I U / Secr. / O ~ .C 1988. 44. 1535. a ) A. Yagasaki, I. Andersson. L. Pettersson. h r g . Cliem. 1987. 26 3926; h) L Pettersaon. I. Andersson. L . - 0 . Ohman. ;hid 1986. 15. 4726: c) A r m Chiw. S c u d . Sw. A 1985. 39. 53. W. G. Klemperer. C. Schwartr. D . A . Wright, J A n ! . C/wnz. SO(. 1Y85, 107. 6941 D . G . Lyxell. R . Strandberg. D. Bostrom, L. Pettersson. Acru C l i ~ m Scund. . Ser. A 1991. 4.5, 681 K. Moedritzer. R. Irani. J. 0i.g. C/win. 1966, 31, 1603. The "P NMR spectra were recorded on a JEOL 90-FXQ spectrometer at 36.2 MHI with proton decoupling and referenced to external 8 5 % H,PO, Before we were aware of this work we investigated two preparatively versatile reactions in static magnetic fields of varying flux densities. These were the alkylation of aldehydes 1 with alkyl magnesium halides and the reduction of prochiral ketones 2 with complex metal hydrides. The dependence of the enantioselectivity of these reactions on the magnetic flux density was studied. It was found that a static magnetic field of flux density 0.22.1 T was sufficient to achieve considerable enantiomeric excesses in these reactions.[l6]Thus the addition of dimethylmagnesium, methyl magnesium iodide, or ethylmagnesium t-butylalcoholate to benzaldehyde ( I a) or naphthalene-2-carbaldehyde (1 b) in a static magnetic field of flux density 1.2 T leads to ( R ) - or (S)-1-phenylethanol (3a), -1-(2-naphthyl)ethanol (3b), or -1-phenylpropanol (3c), respectively, with enantiomeric excesses of 65, 98, and 57%, respectively. The reduction of phenones 2a-c with lithium aluminum hydride at 1.2 T yielded the ( R ) - or (S)-1-arylethanols 3a-c with similar selectivity (5598 YO r e ) . Significantly lower enantiomeric excesses (1 1 YO, 2.1 T) were achieved in the reduction of butanone 2d to give ( R ) or (S)-2-butanol 3d. Enantioselective Reactions in a Static Magnetic Field H Guido Zadel, Catia Eisenbraun, Gerd-Joachim Wolff, and Eberhard Breitmaier* Absolute asymmetric synthesis (AAS)"] denotes an enantioselective synthesis from achiral starting materials without the help of chiral reagents. An example is the synthesis of hepta- and octahelicenes in circular polarized light with enantiomeric excesses up to 7.3 %.['. 31 Absolute asymmetric synthesis has been discussed as the origin of optical activity in evolution.[4- ' 1 In 1975 P. Gerike introduced a new absolute asymmetric synthesis.['21 He carried out reactions in electric fields (158100 Vcm-') to which parallel, antiparallel, or orthogonal constant or alternating magnetic fields (8 x 103-1.17x l o 5 A m - ' , 0-50 Hz) were superimposed. The formation of oxiranes, the addition of bromine to C-C double bonds, and the alkylation of prochiral ketones with Grignard reagents to form secondary alcohols were studied. The enantiomeric excesses amounted to at most 0.94% without preference for either ( R ) or ( S ) isomer. However, the level of enantiomeric excesses contradicts the theoretical prediction of W Rhodes and R. C. Doughertythat enantiomeric excesses of no more than 3 x YOshould be achievable with magnetic flux densities of up to 1 T. R. C. Dougherty et al. later studied the formation of oxiranes and cyclopropanes at flux densities of "about 1 . I T"[14,151 without, however, the simultaneous application of an electric field. Instead, they spun the reaction vessel at high speeds (600014000 rpm) in order to achieve the desired selectivity with the additional gravitational field.[141As Gerike had reported, they found an irregular preference for the ( R ) or ( S )enantiomer (ee < 1 %), which they traced back to photochemical side-effects (daylight, artificial light), after the influence of the earth's magnetic field had been eliminated by aligning the apparatus with the compass. [*] Prof. Dr. E. Breitmaier, D r . G. Zadel, Dipl.-Chem. C. Eisenbrdun Institut fur Orgdnische Chemie und Biochemie der Universitit Gerhard-Domagk-Strasse 1. D-53121 Bonn (FRG) + Telefax: Int. code (228)73-5683 Dr. G:J. Wolff Bruker Analvtische Messtechnik D-76287 Rhdinstetten (FRG) 454 :(~"VCH Verlu~sResellschaftmhH, 0.69451 WiGnheirn, 1994 RMgX 1 3a 3b 3c 3 R Ar Me Me Et Ph X So[TI UMe 2-naphthyl I OtBu Ph LiAIH, C,H,. Et,O R' I R/'\O R' I 3 R 3b 3c 3d 65 98 57 ca. 2 0 T , 1.5h 2 3a ee[./] 1.2 1.2 1.2 13' Ph 2-naphthyl Ph Et Me Me Et Me 6, [TI ee ("4 1.2 67 0.4 2.1 2.1 68 55 11 When the reactions were repeated under the same flux density the enantiomeric excesses were always reproducible, although which enantiomer dominated was unpredictable. However, in the case of the crystalline 1-(2-naphthyl)ethanoI (3b), we could repeatably demonstrate that by seeding the reaction mixture of 2 b in the magnetic field with the desired isomer of 3 b before the start of the reaction, it was possible to produce the desired isomer. Without the magnetic field the observed enantiomeric excess corresponded to the amount of seed crystals added. The enantiomeric excesses were determined by specific rotation and also by 'Hand I3C NMR measurements in the presence of tns(3-heptafluoropropylhydroxymethylene)-~-~dmphoratoeuropium(Ir1) or -praseodymium(m) as chiral shift reagent (Fig. 1). The absolute configurations of the products were determined by comparison with the known, published directions of rotation. As shown in Figure 2 the enantiomeric excess increases steadily with the magnetic flux density B, within the field range investigated so Far. 0570-0833/94/0404-0454Si 10.00 + .25/0 A n p w . Chrm. In[. Ed. Engl. 1994, 33, N o . 4 COMMUNICATIONS I a' HO H (S)-(-) - 3b f T-r-T-,.IT12.4 12.3 1 12.2 - --r---,---T--~-. 12.1 12.0 11.9 vvww 14.6 14.5 14.4 14.3 14.2 - s The enantiomeric excesses obtained for 1 -arylethanols 3 a-c in the magnetic fields available to us (flux density up to 2.1 T) are comparable to those achieved with other methods of enantioselective synthesis, such as the use of chiral auxiliaries.[' Substantially less preparative effort, good reproducibility, low cost, and minimal environmental impact make enantioselective reactions in static magnetic fields rather attractive within the preparative scales limited by the size of commercial electro- and cryomagnets. From the study of further reactions["] it appears that particularly those reactions between compounds with prochiral polar double bonds and organometallic reagents can proceed enan- ee p/O] 100 - 90 -. 80 -- 70 I' 60 50 40 0 0 A 10 - .- A Experimental Procedure -. A .- 0 0 tioselectively in a static magnetic field. On the other hand, the addition of m-chloroperbenzoic acid to the nonpolar C-C double bond of styrene (which contains a prochiral C atom) in a magnetic field (up to 2.1 T) yields racemic styrene oxide; similarly the [4 + 21 cycloaddition of methyl acrylate to cyclopentadiene in a magnetic field gives racemic endo and exo isomers.['61 The limits of applicability and the elucidation of the mechanism of this asymmetric induction by a static magnetic field requires numerous further experiments. It is unlikely that the precession of polar, prochiral double bonds in a static magnetic field is the (sole) source of the enantioselectivity. The somewhat greater population of the lower energy (and therefore preferred) direction of dipole precession (along and not opposed to the B, direction) could indeed cause the Re- Si face differentiation necessary for the observed enantioselectivity (accessible side outside, protected side inside the precession cone) ; however, the difference in populations would fall far short of that required to explain the enantiomeric excesses obtained." 31 Particularly striking are the high enantiomeric excesses of the 1-arylalkanols. The constant dependence of the enantiomeric excesses on the magnetic flux density (Fig. 2) suggests a regularity; understanding this should further promote the development of the method. A .L 30 .. 2o A 0 Fig. 1. ee Determination with [Eu(hfc)J. Extreme cases: a) (R)-and (S)-3b from I b and methylmagnesium iodide at 0.4 T: ' H N M R signal for the methyl protons (400MHz): 68% re. b) (R)-and (S)-3d , , from reduction of Zd with lithium aluminum hydride at 2.1 T: ' H N M R signal for the C-l methyl protons (400 MHz): 11 % e r . - A : 3a; 0 : 3 b 0.2 0.4 0.6 0.8 1.0 1.2 1.4 B,Vl Fig. 2. Enantiomeric excess of 3a by reduction of Za with LiAIH, and of 3 b by Grignard methylation of I b as a function of the magnetic flux density B, of the static magnetic field. A n g e w Cliem. In[. Ed. Engl. 1994. 33, No. 4 Qj 1. Arylethanols by addition of organometallic compounds to prochiral carbonyl compounds A solution of the aromatic aldehyde (I a,b,c, 1 mmol) in benzene (0.2 mL) was diluted to a total volume of 4 mL with isoamyl ether at room temperature and transferred to a 50 mL three-neck flask fitted with a n inert gas inlet (glass capillary) and reflux condenser. The reaction flask was held in position in the homogeneous region of a regulated electromagnet (7 cm bore). After 5 min a solution of methylmagnesium iodide (1.27 M) in isoamyl ether ( 1 mL ampule, Merck, was added dropwise over 1 h (for the formation of 3 a and 3b). For the preparation of 3a a solution of dimethylmagnesium (1 M) in 1.4-di0xdne:tetrahydrofuran (1: 1 , 1.27 mL) was VCH Verlug.~gesellschufimbH, 0-69451 Weinheim,1994 0570-0833194jO404-0455$ 1 O . O O t .2S!O 455 COMMUNICATIONS also used. The preparation o f 3 c was carried out in the same manner with 1.27 mL of a solution ofethylmagnesium rerr-butylalcoholate in 1.4-dioxane (1 M ) . To ensure mixing a slow stream of nitrogen was bubbled through the solution. The reaction was quenched by addition of water (5 mL) and worked up by pouring the resulting mixture into saturated ammonium chloride solution (10 mL). After separation of the organic phase. the aqueous phase was extracted with diethyl ether ( 3 x 10 m L ) . The combined organic phases were washed with saturated aqueous sodium bisulfite solution ( 5 mL) and dried with magnesium sulrate: the solvent was removed under vacuum (18 hPa, 13 Torr). I-Phenylethanol ( 3 a ) . Yield 56%: b.p. 83 C ( I X hPa). 6 5 % ('c ( N M R ) at 1.2T: = 29 9 (i.= 1.08 in toluene): pure enantiomer: [x];" = k46.3 (< = I i n toluene). + [z];" 1-(2-Naphthyl)ethanoI(3b): Yield 40%; m.p. 68-70 C; 9 8 % i'c ( N M R ) at 1.2 T: [&" = - 36.8 (L. = 1.24 in methanol); pure enantiomer: [XI;''= +38 (k0.5) (i.= 1 in methanol). for further cWB, pairs see Figure 2. I-Phenylpropanol (3c): Yield 6 0 % , b.p. 96 C (18 hPa): 57% ee ( N M R ) at 1 . 2 T ; + 26.8 ( L = 1.8 in hexane): pure enantiomer: [XI;" = k46 48 ( l = 2.2 in hexane) [I]:" = 2. Secondary alcohols by reduction ofprochiral carbonyl compounds with complex metal hydrides Lithium aluminium hydride (0.08 g, 2 mmol) was covered with anhydrous T H F (ca. 2 inL). Anhydrous benzene was then added to give a total volume of 6 m L . The apparatus was inserted in the magnetic field; 5 min latei- the carbonyl compound ( 2 a d. 1.7mmol in the same volume of benzene) was added dropwise over 1 h. After an additional 15-30 min the reaction mixture was removed from the magnetic field and carefully quenched with water (5 m L ) . The norkup consisted of pouring the reaction mixture into saturated ammonium chloride solution (10 mL). extracting the alcohol with diethyl ether. and drying the solution over MgSO,, and removing the solvent by distillation. For the production of a particular enantiomer of 3 b the reaction mixture was seeded in the magnetic field with 0.04 mmol (7 nig) of the desired isomer before the addition of the carbonyl compound 2b. 3 a : Yield 98%; b.p. 83 C (18 hPaj: 67% ~7e(NMR) at 1.2 T: [I];" = + 31.4 (c = 1 . 3 in toluene); pure enantiomer [z];" = k46.3 ( 1 , = 1 in toluene): for further e(,:B0 pairs see Figure 2. 3b:Yield9Xi%;m.p.68 -70 C : 6 X 0 ~ e c ( N M R ) a t 0 . 4 T : [ a ] ~=" - 2 5 . 8 ( ~ . = 1 . 3 i n methanol), 52% (v at 0.25 T (average of 5 seeding experiments); [.]in= -19.3 ( c = 1 . 3 in methanol). pure enantiomer: [XI;" = k38 ( k 0 . 5 ) (L. = 1 in methanol). 3c: Yield 8 8 % . b.p. 96 C (18 hPa). 5 5 % m ( N M R ) at 2 1 T[T];" = + 25.4(? = 2.1 in hexane); pure enantiomer [&" = 246-48 ( c = 2.2 i n hexane). 3 d : Yield 98% (GC): b.p. 99-10O-C, 11% ce (NMR) at 2.1 T (average of nine experiments); [x]:" = - 1.09 (neat): pure enantiomer [I];" = k10 -12.5 (neat). Received: August 20. 1993 Revised: December X. 1993 126306IEI German version: A f i p i i . Chein. 1994. 106. 460 [ i ] B. Bredig. P. Mangold. T. G. Williams. Afigeii. C/iw7. 1923. 36, 456  W. J. Bernstein. M. Calvin. 0. Buchardt, 1 Ani. C h i . Soc. 1972. 94,494: ihid. 1973. 95. 527; E~trahcdronLet[. 1972, 2195. [ 3 ] H. Kagan. A. Moradpour. J. F. Nicoud. G. Balavoine. R H. Martin. J. P. Cosyn, Terrohr~lro~i Lerr. 1971, 2479.  A. I. Oparin. Origiif of Li/c, 3rd ed.. Academic Press. New York, 1957. IS] I. Keosian. Tlir O q r n Of L ~ / P2nd . ed.. Rheinhold. New York. 1968.  G. Wald. Ann. N . Y Acurl. Sci. 1967, 69. 352: Clwn. A h t r . 1966, 6 6 , 14093g.  A. S. Garay. N u m v ( L o d i n ) 1968. 219. 338. Orgrinre Reuctioi7r. Prentice Hall. [XI J. D. Morrison. H. S . Mosher. A.~,wirw(~rric London. 1971.  P. Curie. J. P / i w . Rarliur7i 1894. 3. 409 [lo] A. Gupta. G . S. Hammond. J. Chein. P h w 1972, 57. 1789; Cherii. Ah.srr. 1972. 77. 953 191. [ I l l T. L. V. Ulbricht, Q. R o , . Chenf. S O L .1959. 13. 48. C/irni. Ahsrr. 1959, 53, A Stannanediyl with a Tin-Carbon Multiple Bond** Hansjorg Griitzmacher,* Werner Deck, Hans Pritzkow, and Michael Sander Dedicated to Projessor WoL&ang Sundrumeyer on the occasion o f h i s 65th birthday According to a model from Trinquier and Malrieu, the structures of compounds with the formula R,X=YR, can be correlated with the singlet- triplet excitation energy BE,,,,, of diylene, R,X: (X, Y = C, Si. Ge. Sn)."] When the relationship CAEls,,, < 112 E, + ( E , + = total bond energy) is fulfilled, "classical" planar molecular structures, such as ethylene, are formed (CAE,,,,,~-20 kcalmol-'; 1/2Eo+ n = 86.6 kcal mol - I ) . If, on the other hand. CAEls,,, > 1/2 E, + n. "non-classical" double bond systems are predicted, with the molecular fragments occupying trans positions being bent with respect to the plane of the X = Y double bond.['] The best known example is the distannene 1, which was investigated by Lappert et al. The R,Sn molecular fragments in this molecule are bent to the extent of 41 'I3] (CAE0,,,z45 kcalmol-'; 1/2 E,, + n < 35 kcalmol-', calculated values for H,Sn=SnH,[I1). Investigations on borderline cases, such as compounds with tin-carbon multiple bonds, are particularly interesting. Depending on the substituents, these compounds can belong to either the one double bond type, or the other, due to the weak nature of the tin-carbon bond in stannaethenes, R,Sn=CR; (ca. E, + < 70 kcal mol- I ) . These compounds may also, therefore, be considered as carbene-fragment transfer reagents. The intermediate behavior of stannaethenes has been discussed;14] however, only a few compounds, such as 2 and 3, have been isolated, of which the latter was structurally characteri ~ e d . ' ~The ' ] tin-carbon bond in 3 is short. in spite of the severe twisting of the molecular fragments, and has essentially been attributed to electrostatic interactions. We recently described the stannaketenimine 4,with its considerably bent Sn-C-N arrangement. as being a weakly bonded adduct formed from an isonitrile and a ~tannanediyl.'~'Both fragments have singlet tBu .C =N Mes n 3 R = CH(SiMe3)* tBu R' 4 = 2,4,6-Pr3C,H, 'R = 2,4,6-CF3C,H, 11 18921 [I21 P. Gerike. i v o r o ~ ~ i ~ i . ~ . ~ i ~ r i197.5. a ~ l i u62. / / ~38. ~ii ground states, so the relationship CAE,,,,,> 1/2 E, + is satis W. Rhodes. R. C . Dougherty. J A i m C'heiii. SO?.1978. 100. 6247. fied. We have now investigated the reaction of the stannanediyl  R. C. Dougherty. 1 h i . C'heni. Soc. 1980. 102, 380, 382. 516]with the ketene ylide 6,['] and are able to report on a new [lS] K Piotrowska. D Ednards, A. Mitch. R. C. Dougherty. ~ ~ u r u r i i ~ i . s s m . ~ r . / ~ ~ i f t n i 1980. 67. 442. [I61 G. Zadel, Dissertation, Universitit Bonn, 1993; Patent application June 1 with [*] Prof. Dr. H. Grutzmacher, Dr. W. Deck Bruker Analytische MeDtechnik, C. Eisenbraun. Dissertation. Universitit Institut fur Anorganische und Analytische Chemie der Universitit Bonn. in preparation. Albertstrasse 21. D-79104 Freiburg (FRG) [I71 B. Weber, D. Seebdch. A n p w C%riii. 1992. fO3. 96: Aiizew Clicwi. I n / . 6 1 . Telefax: Int. code + (761)203-5987 D7,$ 1992. 31. 84. Dr. H. Pritzkow. Dipl.-Chem. M. Sander Anoreanisch-chemisches lnstitut der Universitat Im Neuenheimer Feld 270. D-69120 Heidelberg (FRG) [**I This work was supported by the Deutsche Forschungsgemeinschaft (SFB 247) and the Fonds der Chernischen Industrie.