7a-Acetoxydihydronomilin: isolation, spectra, and crystal structure1

FARID R . AHMED' Dilvisiotl of Biologic.er1 Scietlcps, Notiorlcrl Researcl~ Corrtlcil c~f'Cco~aclcr, Ottcr\vo, Otlt., Ccrt~crcla KIA OR6

AND

ANC S. N c

AND

ALEX G. FALLIS Deptrrtrtletrt of Cl~ernistr)', Mertloritrl Utlil'ersity c!fN~n!forit~cll~t~d, St. JO~III'S, Nfld., Ctrtlciela AIC5S7

Received November 2 I , 1977

FARID R. AHMED, ANG S. NG, and ALEX G. FALLIS. Can. J. Chem. 56, 1020 (1978). Methanol extraction of the ground seeds of Utzcaria Gambier Roxb. followed by chromatog-

raphy afforded a crystalline C30H38Ol0 terpene. This has been shown by X-ray analysis t o be 7a-acetoxydihydronomilin. The crystals are orthorhombic, P2,2,2,, a = 13.158(2), b = 17.092(2), c = 12.689(2) A, Z = 4, dx = 1.300, do = 1.300 g ~ m - ~ . The structure has been determined by the direct method and Fourier syntheses, and refined by block-diagonal least- squares to R = 0.042 for 2621 observed reflexions. The molecule contains a seven-membered lactone ring A, three six-membered rings B, C, D, a three-membered ring E, a furan ring F, and two acetate groups. A and B are chair, C is twist-boat, D is 1,3-diplanar, while E and F a r e planar. The A/B, B/C, C/D junctions are trntu, DIEis cis, and F i s linked to D by an equatorial C-C bond. The two acetate groups are in axial positions on A and B and are cis to each other. The 0 atom forming the apex of the three-membered ring is wedged between two H atoms and their parent C atoms at short intramolecular distances 0 . . . H = 2.28(2) and 2.28(3), and 0. . .C = 2.623(3) and 2.668(4) A. No intermolecular hydrogen bonding is indicated.

FARID R. AHMED, ANG S. NG et ALEX G. FALLIS. Can. J. Chem. 56, 1020 (1978). L'extraction par le methanol de grains concasses de Uncaria Gnrnbier Roxb. suivie par une

chromatographie fournit un terpene cristallin de formule molCculaire C30H38010. On a montr i par diffraction de rayon-X qu'il s'agit de l'acetoxy-7 dihydronomoline. Les cristaux sont orthorhombiques P2,2,2,, n = 13.158(2), b = 17.092(2), c = 12.689(2) A, Z = 4, dx = 1.300, do = 1.300 g ~ m - ~ . On a determine la structure par une mkthode directe et des syntheses de Fourier et on I'a affinee par la methode des moindres carres (blocs diagonaux) jusqu'k une valeur de R de 0.042 pour 2621 reflexions observees. La molCcule contient un cycle lactonique a sept chainons (A), trois cycles a six chainons (B, C et D), un cycle a trois chainons (E), un cycle furannique (F) et deux groupes acetates. Les cycles A et B sont dans la conformation chaise, le cycle C est dans une conformation bateau dkforme, le cycle D est diplanaire-1,3 alors que E e t Fsont plans. Les jonctions A/B, B/Cet C/D sont tmns, DIEest cis et Fest lie a D par un lien equatorial C-C. Les deux groupes acetates sont en positions axiales sur A et B e t sont cis l'un par rapport a I'autre. L'atome d'oxygene formant le sommet du cycle a trois chainons est calk entre deux atomes d'hydrogtne et leurs atomes de carbone a des distances intramoldcu- laires courtes 0. . . H = 2.28(2) et 2.28(3), et 0. . . C = 2.623(3) et 2.668(4) A. I1 ne semble pas exister de liaison hydrogene intermoleculaire.

[Traduit par le journal]

Introduction bination of column and thin-layer chromatography

The plant, Uncaria Gambia Roxb., a member of afforded crystalline material, mp 265-266°C.

the ~ubiaceae family is common to Singapore and Malaysia, where the concentrated aqueous extract of the leaves and stems has been used as a tanning material called Gambir. A few alkaloids (1) have been isolated from these plant extracts but the other chem- ical components have received little attention. We report herein the results of methanol extraction of seeds of Uncaria Gambier Roxb. which after a com-

'NRCC No. 16494. 'To whom all correspondence should be addressed.

Results and Discussion This material was very sensitive to treatment with

aqueous base or acid, and simple degradation prod- ucts could not be isolated in pure form. The molec- ular ion peak at m/e 558 in the mass spectrum and elemental analysis were consistent with the molecular formula C3,H3,01,. A strong, broad infrared ab- sorption at 172&1740 cm-I indicated the presence of several carbonyl functions; possibly esters and/or lactones. Two methyl carbonyl signals, probably due

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AHMED ET AL. 1021

to acetates, could be clearly identified at 6 2.06 and 6 2.16 ppm in the 'Hmr spectrum. This was further supported by the loss of two acetic acid units in the mass spectrum which gave rise to a signal at mle 438.

Weak absorptions at 1630 cm-' and 3140 cm-' in the ir spectrum indicated that some of the 12 double bond equivalents in the molecule are due to double bonds. The nature of this unsaturation was consistent with a furan moiety, the two a hydrogens giving rise to a signal at 6 7.40 ppm ( J = 2 Hz) in the 'Hmr spectrum, with the remaining p proton ap- pearing as a doublet ( J = 2 Hz) at 6 6.32 ppm. Another singlet at 6 5.60 ppm could arise from a single proton attached to a trisubstituted double bond but in view of the X-ray analysis (vide inf,.a) must be assigned to a hydrogen attached to the epoxide ring a to a lactone carbonyl function. Simi- larly the single proton adjacent to the furan ring at- tached to the carbon bearing the lactone oxygen appeared as a singlet at 6 3.51 ppm. The secondary hydrogens on the carbons bearing the acetate func- tions appear as broad single proton multiplets at 6 4.84 and 6 4.50 ppm while the broadened doublet at 6 3.15 ( J = 4 Hz) is due to the two protons a to the carbonyl group.

Concurrent with further chemical studies the X-ray analysis was undertaken and permitted the assignment of structure 1 (7~-acetoxydihydronoini- lin) to this material. The closely related parent ter- pene nomilin (2) has been identified by Dreyer (2) in grapefruit after being isolated earlier by Emerson (3). These molecules are members of a large family of limonoid bitter principles and structure 1 is con- sistent with the spectral data reported above. The 13Cmr spectrum is presented in Table 1. These assign- ments are made by analogy with similar limonoids which have been reported in the literature and the data for khivorin (3) are included for comparison (4).

0

OAc

Relatively few X-ray studies of these natural prod- ucts have appeared (5) and stereochemical assign- ments have been based on spectral interpretation. The X-ray analysis clearly establishes the stereo- chemistry of the furan substituent at C(17) and the C(1) acetoxy function, both of which are a. Thus, it is

TABLE 1. 13Cmr chemical shifts (CDCI,; 6, ppm; Me,Si standard)

6,

Carbon 7ci-Acetoxydihy- atom dronomilin Khivorin

13 34.4 38.8 14 69.7 69.7 15 56.8 56.4 16 or 3 167.3 167.6 17 78.1 78.4 20 120.4 120.5 22 109.9 109.9 2 1 141.1 143.0 23 143.2 141.1 Acetate c==o Acetate Me

Methyl 23.6 27.4 21.6

Signals 18.3 17.3 16 .4

highly likely that the parent nomilin system possesses the same stereocheinical features and the original assignment (6) of the C(1) acetoxy group to the P position, based on an 'Hmr argument, is in error and should be reversed.

Crystal Structure A side-view of the molecule showing its conforma-

tion and the numbering system is presented in Fig. l . The molecule contains three six-membered rings forming the triterpene skeleton to which a three- and a seven-membered ring are fused. A furan ring is linked to the triterpene through a C-C bond in an equatorial position. Five of the rings form a slightly corrugated ribbon that is shaped approximately into a circular arc as shown in Fig. 1, with the three- membered ring in an axial position o n the outside surface of the ribbon and the two acetate groups in axial positions on the inside surface. The A/B, BIC, C/D junctions are all trans, while the DIE is cis, as shown by the torsion angles given in Table 2. The absolute configuration has not been determined, and

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1022 C A N . J . CHEM.

FIG. 1. A side-view of the molecular structure of 7a-acetoxy- dihydronomilin, C30H,80,0, showing its conformation and the numbering scheme. The absolute configuration may corre- spond to this figure or its enantiomorph.

may correspond to the drawing in Fig. 1 or its enantiomorph.

The molecular formula, bond lengths, valency angles, and the rings' torsion angles are given in Fig. 2. Some of the valency angles and torsion angles which could not be fitted in Fig. 2 are compiled in Table 2. These measurements have not been cor- rected for atomic thermal vibration. The 21 C(sp3)- C(sp3) bonds are in the range 1.471-1.588(4) A and their mean is 1.540 A. The longest are those in the bond sequence C(4)-C(5)-C(lO)-C(9)-C(8)- C(14) of lengths 1.556, 1.563, 1.588, 1.553, 1.570 (4) A, respectively, and the shortest is C(14)-C(15), 1.471 A, which is common to rings D and E. Four of the C(sp3)-C(sp2) have normal lengths 1.488- 1.506(5) A, mean = 1.499 A, but the C(24)-C(25) which is observed as 1.459(5) A is rather short and may be severely affected by thermal motion. All the other bond lengths are fairly close to their expected values. The C-H are of lengths 0.84-1.12(4) A, mean = 0.98 A.

The mean valency angles in the six-membered rings B, C, D are 110.7, 112.2, 114.8", respectively, with the largest C-C-C angles being C(8)- C(14)-C(13) = 119.2(2)" and C(14)-C(15)- C(16) = 119.3(2)" which appear to result from the fusion of rings D and E at C(14)-C(15). The mean angle in the lactone ring A is 117.7" with the largest being C(3)-O(1)-C(4) = 129.0(2)", while the mean for the furan ring is 108.0".

The view of the molecule shown in Fig. 1 and the torsion angles listed in Fig. 2(c) indicate clearly the conformation of the rings as: A chair, B chair, C twist-boat, D 1,3-diplanar, E planar, and F planar (x2 = 0.9). The C20, atoms of each acetate group are coplanar, with x2 = 0.02 and 0.05 for the two groups. While C(l) is in the plane of its adjacent acetate group, C(7) is 0.055 A away from the plane

VOL. 56. 1978

a

FIG. 2. Schematic drawings of the molecule showing: (a) bond lengths (A), (b) valency angles (deg), and (c) torsion angles (deg) within the rings. The estimated standard devia- tions are 0.003-0.005 A for the bonds and 0.2-0.3" for the angles, excluding the contribution of the parameters' cova- riance.

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AHMED ET AL.

TABLE 2. Some valency and torsion angles (deg) not listed in Fig. 2 (a) Valency angles

Valency angles Value Valency angles involving H Value

(6) Torsional angles

Bonds Angle

of the second acetate group. Also, C(17) lies in the plane of its adjacent furan ring.

The equations of the mean planes of the rings and acetate groups, and some of the dihedral angles be- tween them are summarized in Table 3. The curvature of the molecule is almost uniform as shown by the

TABLE 3. Mean planes and dihedral angles (deg). The planes are in the form IX + t11Y + 12Z - p = 0, where X, Y, Z , p are in A. The planes are identified in Fig. 2(c); Ac(1) and Ac(7)

are the substituent groups at C(l) and C(7)

(a) Planes

Plane I 111 I I P

A -0.6136 0.5288 -0.5864 1.2788 B -0.3295 0.6061 -0.7239 1.3278 C -0.0140 0.6159 - 0.7877 1 ,9900 D 0.1935 0.5198 -0.8321 2.1507 E -0.7735 -0.3665 -0.5171 -6.4905 F 0.7650 0.0807 -0.6389 3.5316 Ac(1) 0.8875 0.3203 -0.3315 0.7061 Ac(7) 0.9395 0.0410 - 0.3400 1.6886

(6) Dihedral angles

Planes Angle Planes Angle

A-B 18.7 D-E 84.8 B-C 18.5 D-F 43.8 C-D 13.4 A-Ac(1) 79.6 A-D 49.9 B-Ac(7) 87.8

Ac(1)-Ac(7) 16.3

dihedral angles A-B, B-C, C-D of 18.7, 18.5, and 13.4", respectively, which add up to 50.6" while A-D is 49.9".

0(3), the apex of the three-membered ring, has four close intramolecular neighbours: C(17) and C(30) a t distances 2.623(3) and 2.668(4) A, and their associated H atoms at 2.28(2) and 2.28(3) A from O(3). The angles associated with these short con- tacts are listed in Table 2, and the corresponding C-H are 1.03(2) and 1.01(3) A. Also, it should be stated that H(17) is only 0.56 A from the mean plane of 0(3), C(14), C(13), C(17); and H(30, 1) is 0.45 A from the mean plane of 0(3), C(14), C(8), and C(30). This information is provided for the benefit of those interested in the study of C-H. . . O hydrogen bonds which may be present in this structure. How- ever, for the lack of a proper analysis of the electron charge distribution in the molecule, the true nature of these contacts cannot be stated at present.

All the other intramolecular 0 . . . H contacts are 22.33 A, and the H . . . H contacts are 2 1.88 A. There are no unusually short interinolecular van der Waals contacts which might be indicative of hydro- gen bonding, and the molecules are therefore held together by electrostatic forces.

Experimental Melting points were determined on a Fisher-Johns melting

point apparatus and are uncorrected. Elemental microanalyses

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CAN. J . CHEM. VOL. 56. 1978

TABLE 4. Atomic fractional coordinates ( x lo4 for C and 0 , x lo3 for H)

Atom xl f l ylb Z / C Atom 4 f l ylb z/c

(31) - 6(2) 4071 (2) 3610(2) H(1) 25(2) 461(1) 379(2) C(2) - 1 133(2) 4060(2) 3887(2) H(2, 1) - 117(2) 435(2) 45 l(2) C(3) -1537(2) 3262(2) 4137(2) H(2, 2) - 149(3) 428(2) 334(3) C(4) - 1 159(2) 2708(2) 2331(2) H(5) 340) 268(1) 275(2) c(5) - 34(2) 2980(2) 2230(2) H(6, 1) 230) 215(2) 102(2) (36) 41 5(2) 2734(2) 1 152(2) H(6, 2) 17(2) 307(2)

1570(2) 67(2)

c(7) 2754(2) 1 164(2) H(7) 184(2) 255(1) 2000(2)

5 1 (2) c(8) 3567(2) 1411(2) H(9) 173(2) 342(1) 298(2) c(9) 1497(2) 3859(1) 2446(2) H(11, 1) 154(3) 509(2) 256(3) c(10) 291(2) 3841(2) 2471(2) H(11, 2) 182(2) 474(2) 359(2) C(11) 1938(2) 4649(2) 2805(3) H(12,l) 319(2) 505(2) 194(2) C(12) 3080(2) 4756(1) 2609(2) H(12, 2) 343(3) 505(2) 323(3) C(13) 3648(2) 3973(1) 2533(2) H(15) 355(2) 244(1) C(14) 31 79(2) 3528(1) 1592(2) H(17) 483(2) 440(1) 154(2)

84(2)

C(15) 3831(2) 2898(2) 11 83(2) H(18, 1) 367(3) 381(2) 417(3) C(16) 4869(2) 2776(2) 1657(2) H(18, 2) 403(4) 307(3) 354(4) C(17) 4770(2) 4126(1) 2261(2) H(18, 3) 296(4) 324(2) 370(4) C(18) 3580(2) 3495(2) 3558(2) H(19, 1) 23(3) 497(2) 165(3) C(19) - 185(2) 4464(2) 1745(3) H(19, 2) - 91(3) 460(2) 192(4) C(20) 5364(2) 4565(2) 3080(2) H(19, 3) -28(3) 431 (2) 101 (3) C(21) 6031(2) 4259(2) 3859(3) H(21) 617(2) 374(2) 402(2)

I C(22) 6393(2) 4858(2) 4406(3) H(22) 685(3) 488(2) 495(3) C(23) 5374(3) 5340(2) 3224(3) H(23) 503(2) 579(2) 287(2)

i c(24) 737(2) 3781(2) 5290(2) H(25, 1) 124(4) 324(3) 656(4) C(25) 1244(3) 3 173(3) 5904(3) H(25, 2) 177(4) 288(3) 547(4) C(26) - 1240(3) 1846(2) 2065(3) H(25, 3) 69(4) 267(3) 584(4) C(27) - 1954(3) 3 165(3) 1708(3) H(26, 1) -73(3) 152(2) 245(3) C(28) 1920(2) 146 l(2) 1828(3) H(26, 2) - 182(3) 163(2) 232(3) C(29) 2279(3) 1039(2) 2784(3) H(26, 3) - 122(3) 177(2) 131(3)

I C(30) 1832(2) 4103(2) 444(2) H(27, 1) -259(3) 288(2) 179(3) I O(1) - 1466(2) 2681(1) 3447(2) H(27, 2) - 177(3) 329(2) 105(3) I o(2) 5314(1) 3381(1) 2132(2) H(27, 3) -205(2) 376(2) 195(2) 1 o(3) 3750(1) 3615(1) 623(1) H(29, 1) 243(4) 47(2) 264(3)

I O(4) 5999(2) 5544(1) 4037(2) H(29, 2) 171(5) 108(3) 339(5) I o(5) 502(1) 3535(1) 4316(1) H(29, 3) 292(5) 132(3) 3 14(5)

O(6) 542(3) 4428(2) 5589(2) H(30, 1) 224(3) 391(2) - 17(3) O(7) - 1927(2) 3119(1) 4977(2) H(30, 2) 120(3) 414(2) 23(3)

I O(8) 1935(1) 2236(1) 1994(1) H(30, 3) 200(3) 464(2) 1658(2)

60(3) o(9) 1 170(1) 1026(2) O(10) 5303(2) 2154(1) 1604(2)

were performed by Beller Microanalytical Laboratory, West The concentrated benzene fraction was chromatographed Germany. on silica gel. The column was eluted with petroleum ether fol-

Infrared spectra were recorded as KBr pellets on a Perkin- lowed by petroleum ether - d~ethylether and fractions (-50 Elmer 567 or 710A grating spectrometer and were calibrated ml) were combined o n the basis of similar Rr values on tlc against the 2850 and 1601 cm-' bands of polystyrene film. slides. Crystalline material was obtained from the more polar 'Hmr spectra were determined in CDC1, with a Perkin-Elmer fractions and was recrystallized with difficulty from methanol, R-12B or Varian HA 100 spectrometer; band positions are mp 265-266°C. The 7a-acetoxydihydronomilin had the fol- reported in parts per million downfield from tetramethylsilane lowing spectral properties: ir (KBr) 3140 (CH=C), 1720-1740 as an internal standard; 13Cmr spectra were recorded on a ((LO), 1630 (C-C), 875 (furan) cm-'; 'Hmr (CDCl,) 7.40 Varian XL 100 instrument. Mass spectra were recorded by (2H, d, J = 2 Hz, furan), 6.32 (lH, d, J = 2 Hz, furan), 5.60 Morgan-Schaeffer, Montreal. (lH, s, H-C-0), 4.84 (lH, m, HCOAc), 4.50 (lH, m,

HCOAC), 3.51 (lH, s, H-C-O), 3.15 (2H, d, J = ~ H z , Extrnctiolz n l~d Zsolatio~z -CH2CO) ppm; ms: M* 11i/e 558, calcd. 558. Allal. calcd. for

Fresh seeds of Uilcflrifl Gnnlbier R0.Yb. collected in the c ~ ~ H ~ ~ ~ ~ ~ c 64.50, H 6.86, 0 28.64; found: c 64.30, H 7.12, botanical garden in Singapore were separated from their nut 0 28-58. husks and crushed using a blender. The ground seeds (1500 g) were stirred mechanically in methanol (3000 ml) for 48 h at C.,,,tal room temperature. The mixture was filtered and the residue re-extracted with fresh methanol. The combined brownish red C30H38010 fw = 558.63 extracts were concentrated to approximately half the original OrthOrhombic, P212121, = 13.158(2)7 =

I volume under reduced pressure on a rotary evaporator and 17.092(2), c = 12.689(2) A, V = 2853.7 A3, z = 4, D, = 1.300, further extracted with petroleum ether followed by benzene Do = ls300 g cm-3, F(OOO) = llg2, dCu Ka) = 7.68 cm-'l

(700 ml portions in a separatory funnel). h(Cu Kal) = 1.54050, h(Cu Kg2) = 1.54434 A.

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AHMED ET AL. 1025

The space group was uniquely determined from the sys- tematic absences on precession photographs. The unit-cell parameters were derived from the 20 values of some high-order axial reflexions. The crystal density was measured by flotation in aqueous K I solution at 26°C.

Intensities The intensity data were collected on a Picker diffractometer

with the 9-20 scan method, using a prismatic crystal (0.4 x 0.6 x 0.3 mm) and Cu(Ka) radiation to (sin 0/h) limit of 0.588. The 20 scans covered 2" for 20 = 0-10O0, and 3" for 20 = 100-130". The background corrections were derived from an empirical curve expressed as a function of 20. The (006) was used as a monitor reflexion for scaling purposes, and its intensity showed a small random variation of 1 2 % throughout the experiment. The net intensities were corrected for the Lorentz-polarization effect, but not for absorption. The total number of reflexions scanned was 2740, of which 2621 reflexions (95.8%) were observed above background.

Structure Detennit~ntio~~ The positions of the 40 non-hydrogen atoms were deter-

mined from an E map and two Fourier syntheses. The E map, calculated from 328 reflexions with lE( 2 1.40, showed two images of the molecule separated by a prominent C-C bond vector parallel to a. This map was interpreted as described by Huber (7) by placing the molecule halfway between the two images. Twenty of the atomic positions were accepted from this map, and the other 20 positions were derived from two successive Fourier syntheses. At the start, C atoms were placed at most of the atomic positions and their parameters including the occupancies and isotropic temperature factors were refined by three cycles of block-diagonal least-squares calculations. The possible 0 positions were then identified on the basis of their occupancies and bond lengths. At that stage, the occu- pancies were 0.91-1.25 for the C sites and 1.23-1.44 for the 0 sites, with estimated standard deviations of 0.04-0.05. The occupancies were then fixed a t 1.00 for all atoms and the parameters were refined anisotropically. Finally the H atoms were located from three difference maps calculated a t later stages, and were refined isotropically. The refined atomic posi- tions are listed in Table 4.3

The quantity minimized in the least-squares refinement was Cw((F,I - IFcl)Z, where w = l /{ l + [(jF,l - 15)/4014} and 1.53 5 IF,( 5 154.1. All the unobserved reflexions, as well as eight very strong reflexions showing extinction effect, and one

-

3The atomic thermal parameters and the structure ampli- tudes are available, at a nominal charge, from the Depository of Unpublished Data, CISTI, National Research Council of Canada, Ottawa, Ont., Canada K I A OS2.

weak reflexion were excluded from the refinement. In the final cycle, the mean (A/o) = 0.22, maximum (A/o) = 0.77 for C and 0 (= 2.1 for H); R = 0.037 and R, = 0.039 for the ob- served reflexions excluding those omitted from the refinement (R = 0.042 for all observed reflexions), [Z(wA2)/(rn - t ~ ) ] " ~ = 0.70. There were no outstanding discrepancies in the calculated structure amplitudes of the unobserved reflexions. The residual electron density in the final difference map was randomly dis- tributed within -0.15 and 0.17 e A-3.

The scattering factor curves were those of ref. 8 for C and 0 , and of ref. 9 for H. All computations were performed with the NRCC set of crystallographic computer programs (10).

Acknowledgements

The authors are grateful to Dr. A. W. Hanson for measuring the cell parameters and intensity data, to Mrs. M. E. Pippy for assistance with the cornputa- tions, to Dr. J. Walter for 13Cmr spectra, to the Department of Chemistry, Nanyang University for assistance (to A.S.N.), and to Memorial University of Newfoundland and the National Research Coun- cil of Canada for financial support (to A.G.F.) of this research.

I . L. MERLINI , R . MONDELLI, and G. NASINI. Tetrahedron, 23, 3129 (1967); Tetrahedron Lett. 1571 (1967); Tetrahe- dron, 26.2259 (1970).

2. D. L. DREYER. Phytochem. 5, 367 (1966); seealso D. ARI- GONI , D. H. R . BARTON, E. J . COREY, 0. JEGER, L. CAG- ~107.1, S. DEV, P. G. F E R R I N I , E. R . GLAZIER,A. MELERA, S. K. PRADHAN, K. SCHAFFNER, S. STERNHELL, J . F. TEMPLETON, and S. TOBINAGA. Experientia, 16,41(1960).

3. 0. H . EMERSON. J . Am. Chem. Soc. 70. 545 (1948); 73, 2621 (1951).

4. D. A. H. TAYLOR. J. Chem. Soc. Perkin I , 437(1974). 5. H. R . HARRISON, 0. HODDER, C. W. L. BEVAN, D. A. H.

TAYLOR, and T. G. HALSALL. Chem. Commun. 1388 (1970); S. ARNO-TT, A. W. DAVIE-J . M. ROBERTSON. G. A. S I M , and D. G. WATSON. Experientia, 16, 49 (1960).

6. D. L. DREYER. Tetrahedron, 21.75 (1965). 7. C. S . HUBER. ActaCrystallogr. B31, 108 (1975). 8. H. P. HANSON, F. HERMAN, J . D. LEA, and S. SKILLMAN.

Acta Crystallogr. 17, 1040 (1964). 9. R. F. STEWART, E. R. DAVIDSON, and W. T. SIMPSON. J.

Chem. Phys. 42,3175 (1965). 10. F. R. AHMED, M. E. PIPPY, and C. S. HUBER. J . Appl.

Crystallogr-. 6,309(1973).

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