Proc. Natl. Acad. Sci. USA Vol. 74, No. 6, pp. 2189-2193, June 1977 Chemistry New methylcyclopentanoid terpenes from the larval defensive secretion of a chrysomelid ( versicolora)* (/iridoids/chrysomelidial/plagiolactone) JERROLD MEINWALDt, TAPPEY H. JONESt, THOMAS EISNERf, AND KAREN HICKSt t Department of Chemistry and * Section of Neurobiology and Behavior, Cornell University, Ithaca, New York 14853 Contributed by Jerrold Meinwald and Thomas Eisner, April 11, 1977

ABSTRACT The defensive secretion of larvae of the CH3 o CH3 -Glucose chrysomelid beetle contains two un- stable, volatile methylcyclopentanoid terpenes: a dialdehyde (chrysomelidial) isomeric with dolichodial and anisomorphal, H and a closely related enol lactone (plagiolactone). Chrysomel- idial and plagiolactone are shown to have structures III and IV on the basis of a detailed analysis of their spectra, coupled with H3 CO2CH3 chemical transformations to products of known structure. I II CH3 H3 CHO CH3 H3 CHO / 0 CHO 0 CHO H3 H3 III IV -H3 H3 la IV The structure of nepetalactone (I) was established over 20 years species of Chrysomelidae have comparable discharge mecha- ago (1, 2). At that time this compound, which had been isolated nisms, which have been described (9). Chemical work on the from the essential oil of the mint Nepeta cataria (3), was re- secretion of some of these larvae has led to the isolation of garded chiefly as a chemical curiosity; it had gained some salicylaldehyde from Phyllodecta vztellinae (10), Melasoma low-keyed notoriety because of the bizarre behavioral responses populi (11), and scripta (12), and of fl-phenyl- it was capable of eliciting in a variety of felids of both sexes (4). ethyl isobutyrate and fl-phenylethyl 2-methybutyrate from It subsequently developed, however, that nepetalactone was Chrysomela interrupta (13). It was clear from the odor of the the first recognized representative of the methylcyclopentanoid secretion of Plagiodera that this produces a secretion terpenes, a large and diverse group of natural products based of entirely different composition. on the 1,2-dimethyl-3-isopropylcyclopentane skeleton, whose chemistry was summarized in an extensive monograph pub- EXPERIMENTAL SECTION lished some 15 years later (5). These terpenoids are widely distributed in nature, and members of the group have been Gas chromatographic analyses were carried out using 2.5 m X found to serve many diverse functions, including repel- 2 mm columns packed with 5% OV-1 on Gas-Chrom Q (column lent in plants (6), "anti-aphrodisiac" (ref. 5, p. 136) antibiotic A), 3% OV-225 on Gas-Chrom Q (column B), or 5% FFAP on (ref. 5, p. 136), and insect defense agent (ref. 5, pp. 203-238). Gas-Chrom Q (column C) (packing materials from Applied The recognition of the central role played in the biosynthesis Sciences Laboratories, Inc). Mass spectra were obtained at 70 of many alkaloids by loganin (II), a methylcyclopentanoid eV using a Finnigan model 3300 gas chromatograph/mass terpene glycoside, has provided an important insight into the metabolic link between the alkaloids and the terpenes (5, 7, 8). We wish to report the isolation and characterization of two new methylcyclopentanoid terpene derivatives, chrysomelidial (III) and plagiolactone (IV), from the defensive secretion of larvae of a chrysomelid beetle, Plagiodera versicolora. Plagiodera larvae occur commonly during the summer months on leaves of willow trees (Salix spp.) in the environs of Ithaca, NY. The larvae have nine pairs of glands, arranged segmentally along the sides of the body. They discharge se- cretion readily in response to direct disturbance (Fig. 1). Related

Abbreviations: GC, gas chromatography; MS, mass spectrometry; m/e, mass-to-charge ratio; IR, infrared; NMR, nuclear magnetic resonance; for NMR spectroscopy, s is a singlet peak, d is a doublet, t is a triplet, q is a quartet, m is a multiplet, and br is broad. * This is report no. 56 of the series "Defense Mechanisms of Arthro- FIG. 1. Larva ofPlagiodera versicolora responding to pinching pods." Report no. 55 is Brattsten, L. B., Wilkinson, C. F. & Eisner, ofone ofits legs with forceps by emitting secretion from its segmental T. (1977) Science, in press. defensive glands. (Reference bar = 1 mm.) 2189 Downloaded by guest on September 28, 2021 2190 Chemistry: Meinwald et al. Proc. Natl. Acad. Sci. USA 74 (1977)

spectrometer (GC/MS) coupled with a System Industries model J = 2.5 Hz, CHCHO), 2.2-0.9(15 protons, complex multiplet); 150 computer. High resolution mass spectra were obtained MS, mle 111(4),107(2),97(2),95(2),93(2),91(2),83(20),82(26), using an AEI MS-902 instrument coupled with a VG Data 81(13), 80(5), 79(6), 69(87), 67(39), 58(100), 55(95), 43(20), System 2020 computer. 41(65). Except for the parent peak and the peak for parent ion Hydrogenation of Chrysomelid Secretion. The secretion minus 15 mass units, which were not observed under the con- from 282 larvae was taken up in a few milliliters of ether. This ditions used to obtain this mass spectrum, these data compare solution was added to 1 ml of ether containing 25 mg of 10% well with the data obtained for the major hydrogenolysis Pd/C which had been saturated with hydrogen. The mixture product from the chrysomelid secretion. was stirred for 1 hr under a slight positive pressure of hydrogen. Chrysomelidial and Plagiolactone. Gas chromatographic After filtration and concentration of the solution, GC/MS analysis (column B) of fresh chrysomelid secretion showed two analysis (column A) showed the presence of 7 to 10 peaks de- major components, the first, chrysomelidial, always more than pending on theGC conditions. One of the minor components twice as abundant as the second, plagiolactone. Preparative GC (about 10%) had a mass spectrum identical to that reported for (column B) of the concentrated ether washings of filter paper 1-ethyl-3-methylcyclopentane (V) (14). The major component squares used to absorb the secretion of 2000 larvae gave ap- of the mixture had MS, m/e peaks (relative intensities in pa- proximately 0.2 mg of chrysomelidial as a pale yellow liquid. rentheses) 140(1), 125(4), 111(11), 97(6), 95(3), 93(2), 91(2), IR (CC14) 1720, 1660, 1620 (shoulder) cm-1; NMR (100 MHz) 83(27), 82(45), 81(21), 80(6), 79(7), 69(89), 67(38), 58(100), a 10.19(1, s, C=C-CHO), 9.98, 9.85 (1, s, s, CH-CHO), 3.63 55(82), 43(16), 41(57). This mass spectrum corresponds well [1, br m, C=C(CHO)-CHI, 3.08(1, m, CHCHO), 2.60(2, br with that obtained for synthetic 2-(3-methylcyclopentanyl)- t, CH2C=C), 2.18 (3, s, CH3-CC), 1.02 and 0.89 (3, pair propionaldehyde (VI), prepared as described below. of d, J = 7.2 Hz, CH3CHCHO); there was also an absorption 2e(3-Methylcyclopentylidene)propionaldehyde. This al- at a 1.3 due to water; MS (column C), m/e 166(4), 148(21), dehyde was prepared in low yield using the general method 136(8), 134(8), 120(10), 109(52), 108(39), 107(32), 105(16), described by Meyers et al. (15). A solution containing 5.0 g (32.2 96(10), 95(20), 93(16), 91(19), 82(10), 81(100), 80(25), 79(71), mmol) of 2-ethyl-4,4,6-trimethyldihydro-1,3-oxazine in 30 ml 78(15), 77(26), 67(20), 65(10), 55(22), 53(27), 51(10); calculated of tetrahydrofuran was cooled to -780 and treated with 17.5 mass for CloH1402 166.0994, found m/e 166.0997; calculated ml of 2 M 1-butyllithium. After stirring of the mixture for 1 hr, mass for C7H9O 109.0655, found m/e 109.0632; calculated a solution containing 3.44 g (35.2 mmol) of 3-methyl-1-cyclo- mass for C7H80 108.0575, found m/e 108.0551. pentanone in 10 ml of tetrahydrofuran was added dropwise Approximately 0.1 mg of plagiolactone was also isolated by over 1k hr. The mixture was allowed to warm to room temper- preparative GC of the same ether washings, as a waxy solid ature over 1 hr, poured into ice, acidified with 10% HCI, and which melted as room temperature. This compound had the extracted with pentane. The aqueous layer was then made basic following spectral data. UV XEt1' 244-252 nm, E _ 5,000 M- with 10% NaOH and ice, and extracted with three 75 ml por- cm- 1; IR (CC14) 1764 cm-1; NMR (100 MHz) (assignable sig- tions of ether. The-ether extract was dried over anhydrous nals) 66.53(1, br s, C-CH-0C=0), 5.73(1, br s, HCC), K2CO3 and concentrated under reduced pressure, and the 2.47 (1, d of q, J = 6.6 Hz and 14 Hz), 1.82 (3, br s, CH3- residue was taken up in a mixture of 30 ml of ethanol and 30 C=C), and 1.28(3, d, J = 6.6 Hz, CH3-CH). Decoupling of ml of tetrahydofuran. The pH was adjusted to 7; the mixture the doublet at 51.29 collapsed the doublet of quartets at 52.47 was cooled to -350, and treated with a solution containing 1.22 to a doublet, J = 14.0 Hz; MS, m/e 164(60), 136(21), 121(28), g of NaBH4 in 5 ml of H20 containing 1 drop of 40% NaOH. 109(11), 108(48), 107(49), 106(15), 93(39), 91(45),-80(85), During this addition, the pH was maintained at 6-8 by the 79(100), 78(16), 77(50), 65(16), 53(11), 51(18); calculated mass addition of dilute HCL. After stirring for 1 hr, 30 ml of H20 was for CloH1202 164.0837, found m/e 164.0833; calculated mass added and the mixture was extracted with ether (3 times at 75 for C9H12O 136.0888, found m/e 136.0895; optical rotatory ml each). The ether was dried over K2CO3, and the solvent was dispersion at 18.8 ,g/ml, IbI1275 rnm = -8000, 1l1 240 nm = removed under reduced pressure. After the addition of 50 ml 24,000 degrees cm2 dmol-I (EtOH). of H20 containing 16.2 g of oxalic acid, the mixture was heated Nepetapyrone (Dehydronepetalactone) (XII). A mixture and to reflux for 2%, hr. Upon cooling, the mixture was extracted of 31 mg of nepetalactone, 40 mg of N-bromosuccinimide, with ether, the ether was dried over anhydrous MgSO4, and the 1 ml of CC14 was heated to reflux for 15 min while under a solvent was removed under reduced pressure. Kugelrohr dis- General Electric sunlamp. After cooling, the mixture was fil- tillation gave 0.2 g of a colorless liquid (bp 120-130°/1.0 mm tered, diluted with 3 ml of CC14, treated with 100 mg of 1,5- Hg) which was >95% pure by GC (column A); infrared (IR) diazabicyclo[4.3.0lnon-5-ene, and heated to reflux for 30 min. (neat) peaks at 2880, 2750, 1670, and 1640 cm-1; nuclear The mixture was cooled, washed with 1 M H2SO4, and the or- magnetic resonance (NMR) shifts, 6, in ppm relative to tetra- ganic layer was dried over anhydrous MgSO4. Gas chromato- methylsilane 10.2 (1 proton, s, CHO), 3.0-2.0 (4, m), 1.73 (3, graphic analysis (column B) showed the product to be a 2:5 br s, CH3-C=C), 1.0-1.5 (3, m), 1.1 (3, d, J = 6 Hz, CH3- mixture of nepetalactone and a material with a longer retention CH); MS, mle 138(10), 123(14), 109(12), 107(10), 105(13), time. Preparative GC afforded XII as a pale yellow oil vhich 95(41), 93(16), 91(26), 81(56), 80(38), 79(35), 77(31), 67(71), had IR (neat) 1715, 1690, 1555, 1115, and 940 cm-1; NMR (100 65(27), 57(16), 55(60), 53(53), 52(12), 51(31), 50(12), 43(74), MHz) 5 7.19 (1, s, -CH-OCO), 3.26 (1, br q, J = 7.1 Hz, 41(100). CH3CH-C=C), 2.69 (2, m, CH2-C=C), 2.32 (2, m, CH.), 243-Methylcyclopentanyl)propionaldehyde (VI). A solution 1.93 (3, d, J = 1.2 Hz, CH3-CC), 1.27 (3, d, J = 7.1 Hz, containing 0.2 g (1.4 mmol) of 2-(3-methylcyclopentylidene)- CH3-CH); MS, m/e 164(37), 149(100), 136(26), 121(35), propionaldehyde in 5 ml of ether was stirred with 30 mg of 10% 107(22), 93(35), 91(61), 79(24), 78(11), 77(56), 65(21), 53(14), Pd/C under hydrogen at atmospheric pressure until the uptake 51(17), 43(14), 41(16). This material decomposed on standing of hydrogen ceased. After filtration, GC analysis (column B) at -20° in 2 weeks. showed one major component (>90%). After removal of solvent Iridopyrone (4,7-Dimethylcyclopental elpyran-3-one) under reduced pressure, 0.2 g of a colorless oil was obtained (XIII). A solution of 20 g of cis and trans methyl pulegenates which had IR (neat) 2870, 2705, 1728 cm-1; NMR 6 9.79 (1, d, (16) in 50 ml of ether was reduced with 2.4 g of LiAIH4 in the Downloaded by guest on September 28, 2021 Chemistry: Meinwald et al. Proc. Natl. Acad. Sci. USA 74 (1977) 2191 usual way, yielding 16.2 g (96%) of 1-iso0propylii'y- droxymethyl-3-methylcyclopentane, bp 99-102°/12 mm Hg; IR 3360 cm-1 (OH); MS, m/e 154(12). To a well-stirred mixture of 99 g of pyridine and 53.5 g of CrO3 in CH2Cl2 cooled to -5o was added-15 g of this alcohol. Work-up after % hr gave 9.0 g (68%) of 2-isopropylidene-5-methycyclopentane-carboxal- dehyde as a colorless liquid, bp 79-89°/12 mm Hg; IR 1715 cm-1; MS, m/e 152(12). A solution of 8.1 g of this aldehyde was VI refluxed with 3.7 g of ethylene glycol and a crystal of p-tolu- V 1- enesulfonic acid in 90 ml of benzene in a Dean-Stark apparatus ponents is closely related to iridodial (VII), one of the best for 14 hr to give 8.33 g (80%) of 1-isopropylidene-2-(1,3-diox- known methylcyclopentanoid terpenes of insect origin. In fact, olan-2-yl)-3-methycyclopentane, bp 62-66°/0.6 mm Hg; MS, the previously cited molecular formula (CioH1402), determined m/e 196(1). Ozonolysis of 1 g of this product in ether at -780 from mass spectra, showed chrysomelidial to be isomeric with gave 0.6 g (70%) of 2-(1,3-dioxolan-2-yl)-3-methylcyclopen- dolichodial and anisomorphal, stereoisomeric insect defensive tanone, bp (Kugelrohr) 130-150°/14 mm Hg; IR 1740 cm-1; terpenes with structure VIII (18, 19). Analysis of the 100 MHz MS, m/e 170(1), 73(100). 1H NMR spectrum of chrysomelidial strongly suggested its To a suspension of 300 mg of zinc dust in 40 ml of benzene structure to be that given in formula III (as a mixture of one was added a mixture of 0.53 g of this ketone and 0.58 g of major and one minor stereoisomer). The observation of a pair methyl 2-bromopropionate. After 1.5 hr of reflux, 0.2 g of zinc of upfield methyl group doublets (60.89, J = 7.2 Hz in the major and 0.2 g of bromo ester were added. The mixture was worked isomer, 6 1.02, J = 7.2 Hz in the minor isomer) corresponds to up in the usual way after 2.5 hr of additional refluxing. Gas expectations for the methyl group on the secondary, saturated chromatography (column A) allowed the collection of one peak carbon atom. A downfield methyl group (6 2.18 closely spaced whose retention time corresponded to that of plagiolactone as pair of unequal absorptions) is clearly on the ,B carbon of an a pale yellow, unstable liquid, IR 1720, 1645, 1575 cm-1; MS, a,,B-unsaturated aldehyde moiety, and cis to the aldehyde m/e 164(43), 149(100), 136(23), 135(11), 121(23), 107(21), group (20,21). Two highly deshielded protons (6 9.85 and 9.98; 93(41), 91(68), 79(32), 78(13), 77(53), 65(23), 63(13), 55(15), and 6 10.19, s) are easily identified as the saturated and conju- 53(22), 52(13), 51(28), 50(11), 43(22), 41(15). gated aldehydic protons of III, respectively. The absence of any Hydrogenation of Plagiolactone. A solution containing olefinic proton absorptions, along with the character of the about 0.1 mg of plagiolactone in 1 ml of ether was hydrogenated methyl and aldehyde signals, serves to define structure III for at atmospheric pressure in the presence of 2 mg of 10% Pd/C. chrysomelidial [as well as to rule out any significant equilibrium Analysis by GC/MS using column B showed one major com- concentration of the corresponding enol-hemiacetal structure ponent with the following mass spectrum: m/e 168(6), 109(47), IX, whose analogue seems to make an important contribution 97(20), 96(30), 95(100), 94(30), 91(30), 82(53), 81(76), 79(35), in the case of iridodial (22)]. 78(29), 77(12), 76(30), 74(6), 73(24), 69(24), 68(53), 67(94), 56(20), 55(30), 53(30), 51(30), 43(6), 42(6), 41(35). This is almost H3 H3 identical to that reported for iridomyrmecin (14). CHO CHO DISCUSSION CHO CHO Plaglodera secretion was readily collected by wiping the flanks of stimulated larvae with small pieces of filter paper, from H3 CH2 which the organic components could be eluted with ether. Gas VlI Vill chromatographic examination of freshly prepared extracts showed the presence of two principal volatile components, al- H3 H though changes in GC behavior with time made it clear that these components were unstable. (In fact, the instability of these /0 compounds made their isolation and characterization unusually difficult.) Preparative GC allowed the isolation of only very small quantities of each component. Thus, from 2000 larvae H3 we were able to obtain ca 100 gg of plagiolactone and 200 ,g Ix of chrysomelidial (molecular formulas CloH1202 and C10H1402, respectively, based on high-resolution mass spectra). The mass spectrum provides corroboration for this structure. An early clue to the carbon skeleton of these compounds was Thus, aside from the parent ion at m/e 166 (CQoH1402), two obtained from a microhydrogenation experiment, carried out prominent fragments appear at m/e 109 (C7H90) and 108 on the crude secretion obtained from 282 larvae. Analysis of the (C7H80). The first of these clearly corresponds to the loss of the resultant complex mixture by GC/MS resulted in the identifi- propionaldehyde side-chain from chrysomelidial, giving the cation of two significant products. One minor product (ca 10%) allylic ion X, while the latter is the expected McLafferty re- proved to be 1-ethyl-3-methylcyclopentane (V) (14). The major arrangement product resulting from-cleavage of the same component had a mass spectrum suggestive of 2-(3-methylcy- side-chain along with a y-proton to give XI. clopentanyl)-propionaldehyde (VI), and an independently Plagiolactone, isolated (GC) as a waxy solid, melted at room prepared sample of VI supported this identification (see Ex- perimental Section for details). KH3 FH3 + The isolation of the C8 and C9 methylcyclopentane deriva- CHO

CH3 0 CH2

0 0 0 A..'

CH3 CH3 XlV XV Chemical confirmation of the structure IV was obtained by FIG. 2. Dreiding molecular model of (S,S)plagiolactone, showing a micro-hydrogenation experiment. Hydrogenation of pla- the trans relationship between the hydrogen atoms on the chiral giolactone over 10% Pd/C in ether gave one major tetrahydro centers (arrows). Downloaded by guest on September 28, 2021 Chemistry: Meinwald et al. Proc. Natl. Acad. Sci. USA 74 (1977) 2193 that the methyl group occupies a pseude quat r b-eihereby marked "advertisement" in accordance with 18 U. S. C. mation. An assignment of the absolute configuration of IV can §1734 solely to indicate this fact. negative Cotton effect shown by be made on the basis of the 1. Meinwald, J. (1954) Chem. Ind. (London), 488. plagiolactone, since a correlation has been made between the 2. Meinwald, J. (1954) J. Am. Chem. Soc. 76,4571-4573. absolute configuration of transoid, nonplanar conjugated dienes 3. McElvain, S. M., Bright, R. D. & Johnson, P. R. (1941) J. Am. and the sign of their optical rotatory dispersion curves (24). Fig. Chem. Soc. 63, 1558-1563. 2 shows the probable (S,S)stereochemistry of IV based on these 4. McElvain, S. M., Walters, P. M. & Bright, R. D. (1942) J. Am. considerations. Chem. Soc. 64, 1828-1831. The possibility that plagiolactone is produced biosynthetically 5. Taylor, W. I. & Battersby, A. (1969) Cyclopentanoid Terpene by oxidation of chrysomelidial is an obvious one. One can also Derivatives (Marcel Dekker, New York). imagine that when the tiny defensive droplets are exposed to 6. Eisner, T. (1964) Science 146, 1318-1320. air, autoxidation of the dialdehyde might give rise to the lac- 7. Thomas, R. (1961) Tetrahedron Lett., 544-553. 8. Wenkert, E. (1962) J. Am. Chem. Soc. 84,98-102. tone. Since the unused secretion is taken back into the defensive 9. Garb, G. (1915) J. Entomol. Zool. 7,88-97. glands in Plagiodera, as it is in related larvae (9), it is possible 10. Wain, R. L. (1943) Annu. Rep. Agric. Hortic. Res. Stn., Long that the composition of the secretion changes with storage. The Ashton, Bristol, 108-110. question of whether the potential for temporal variation has 11. Pavan, M. (1953) Arch. Zool. Ital. 38, 157-184. biological significance adds a new dimension to the study of this 12. Wallace, J. B. & Blum, M. S. (1969) Ann. Etomol. Soc. Am. 62, larval defense mechanism. 503-506. Syntheses of chrysomelidial and plagiolactone that confirm 13. Blum, M. S., Brand, J. M., Wallace, J. B. & Fales, H. M. (1972) these structural assignments will be published elsewhere. When Life Sci. 11, 525-531. this work was nearing completion, we learned that a 14. Stenhagen, E., Abrahamsson, S. & McLafferty, F. W. (1974) CioH1402 Registry of Mass Spectral Data (John Wiley & Sons, New dialdehyde and CloH1202 lactone had been isolated and York). characterized independently from another chrysomelid species 15. Meyers, A. I., Nabeya, A., Adickes, H. W., Politzer, I. R., Malone, ( cyanea) by M. S. Blum, H. M. Fales, et al. G. R., Kovelesky, A. C., Nolen, R. L. & Portnoy, R. C. (1973)J. Samples of both compounds were kindly provided by H. M. Org. Chem. 38,36-56. Fales. The two insect-derived aldehydes proved identical to 16. Wolinsky, J. & Chan, D. (1965) J. Org. Chem. 30,41-43. synthetic III. The G. cyanea lactone, however, is not identical 17. Hawthorne, J. O. & Wilt, M. H. (1960) J. Org. Chem. 25, to plagiolactone. Compounds closely related to or identical to 2215-2216. III and IV have also been detected independently by J. E. 18. Cavill, G. W. K. & Hinterberger, H. (1961) Aust. J. Chem. 14, Wheeler and G. W. K. Cavill in secretions from still other in- 143-149. sects, but no direct comparisons have been carried out in these 19. Meinwald, J., Chadha, M. S., Hurst, J. J. & Eisner, T. (1962) Tetrahedron Lett., 29-33. cases. 20. Sadtler Research Laboratories (1970) Sadtler Standard Spectra: Early contributions to this study were made by Dr. Arthur F. Kluge, Nuclear Magnetic Resonance Spectra (Sadtler Research Labo- and we are indebted to Marcia S. Cohen for valuable technical as- ratories, 3316 Spring Garden St., Philadelphia, Pa. 19104), No. sistance. We thank Dr. Brian J. Willis for a generous gift of catnip oil, 9477. S. Daniels, M. Guzewich, T. Schmidt, and C. Smith for help in col- 21. Emsley, J. W., Feeney, J. & Sutcliffe, L. H. (1966) High Reso- lecting Plagiodera, and Dr. Henry Dietrich for identifying the species. lution Nuclear Magnetic Resonance Spectroscopy (Pergamon Partial support by the National Institutes of Health (Grants AI-12020 Press, Oxford), Vol. 2, pp. 735-736. and AI-02908 and Fellowship I-F32-CA05139 to T.H.J.) and the Na- 22. Fish, L. J. & Pattenden, G. (1975) J. Insect Physiol. 21, 741- tional Science Foundation (Grant BMS 75-15084) is gratefully ac- 744. knowledged. 23. Fieser, L. F. & Fieser, M. (1967) Reagents for Organic Synthesis The costs of publication of this article were defrayed in part by the (John Wiley and Sons, New York), pp. 189-190. payment of page charges from funds made available to support the 24. Charney, E., Ziffer, H. & Weiss, U. (1965) Tetrahedron 21, research which is the subject of the article. This article must therefore 3121-3126. Downloaded by guest on September 28, 2021