Structural studies of organoboron compounds. XLIV.' 2,3-Dihydro-3-hydroxy- 2,2-tetramethylene-4H-benzoxazin-4-one and its difluoroboron chelate, 2,2-difluoro-

4,4-tetramethylene-l,3,5-trioxa-3a-azonia-2-borata-2,3,4,5 -tetrahydro- 1H-cyclopenta[a]naphthalene

WOLFGANG KLIEGEL A N D MAHMOOD TAJERBASHI Institut fur Pharmazeutische Chemie der Technischen Universitdt Braunschweig, Beethovenstrasse 55,3300 Braunschweig,

Bundesrepublik Deutschland

AND

STEVEN J. RETTIG A N D JAMES TROTTER Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, B.C., Canada V6T IZI

Received August 10, 1990

WOLFGANG KL~EGEL, MAHMOOD TAJERBASH~, STEVEN J. RETT~G, and JAMES TROTTER. Can. J. Chem. 69,673 (1991). The reaction of 2,3-dihydro-3-hydroxy-2,2-tetramethylene-4H-benzoxazin-4-one, 2, and diethyl ether-boron trifluoride

yields the difluoroboron chelate 2,2-difluoro-4,4-tetramethylene- 1,3,5-trioxa-3a-azonia-2-borata-2,3,4,5-tetrahydr0-1H-cyc10- penta[a]naphthalene, 6, in high yield. There are two crystal forms of 2: 2a, triclinic, P i , a = 8.551(1), b = 9.331(3), c = 7.236(1) A, a = 103.38(2), P 104.68(1), y = 80.37(2)", Z = 2, p, = 1.35 g ~ m - ~ , and 2b, monoclinic, C2/c, a = 17.41(2), b = 10.665(6), c = 12.427(8)A, P = 115.74(5)",Z = 8, p, = 1 .40gcm-3. Crystalsof6aremonoclinic, P2 , /c ,a = 5.354(1), b = 17.654(2), c = 12.844(1) A, P = 100.1 1(2)", Z = 4, p, = 1.48 g ~ m - ~ . The structures were solved by direct methods and were refined by full-matrix least-squares procedures to final R values of 0.046,0.046, and 0.041 for 1712, 1505, and 1675 reflections with I 2 3 4 4 , respectively. In both forms of 2, the structures consist of centrosymmetric &H...O hydrogen-bonded dimers (0 . . .0 = 2.633(2) A for 2a and 2.682(3) A for 2b). The difluoroboron chelate 6 features a five-mevbered chelate ring planar within 0.068(2) A, and bond lengths 0-B = 1.504(3) and 1.5 16(3), F-B = 1.358(3) and 1.359(3) A indicate weak binding of the ligand to the F2B moiety.

Key words: organoboron compound, crystal structure, boron compound

WOLFGANG KL~EGEL, MAHMOOD TAJERBASH~, STEVEN J. RETTIG et JAMES TROTTER. Can. J. Chem. 69, 673 (1991). La rkaction de la 2,3-dihydro-3-hydroxy-2,2-tktram~thylkne-4H-benzoxazin-4-one, 2, avec le complexe Et20/BF3 fournit le

chelate difluorobork, 2,2-difluoro-4,4-tktramkthylkne- 1,3,5-trioxa-3a-azonia-2-borata-2,3,4,5-tktrahydro- 1 H-cyclopenta[a]- naphtalkne, 6, avec un excellent rendement. I1 existe deux formes cristallines du produit 2, soit 2a, triclinique, P i , a = 8,55 1(6), b = 9,331(3) et c = 7,236(1)A, a = 103,38(2), P = 104,68(1) et X = 80,37(2)", Z = 2, p, = 1,35 g cm-3 et 2b, monoclinique, C2/c, a = 17,41(2), b = 10,665(6) et c = 12,427(8) A, P = 115,74(5)", Z = 8 et p, = 1,40 g Les cristaux du produits 6 sont monocliniques, P2'/c, a = 5,354(1), b = 17,654(2) et c = 12,844(1) A, P = 100,11(2)",Z = 4et p, = 1,48 gcm-3. On a dktermine les structures par des mkthodes directes et on les a affinees par la methode des moindres carrks (matrice complkte) jusqu'h des valeurs finales deR de0,046,0,046 et 0,041 respectivement pour 1712, 1505 et 1675 reflexions avec I 2 3u(4. Dans les deux formes du produit 2, les structures se composent de dimkres centrosymktriques rkunis par des liaisons hydrogknes &H...O ( 0 . . . 0 = 2,633(2) A pour 2a et 2,682(2) A pour 2b). Le chelate difluorobork 6 est caractkrisk par un cycle h cinq chainons, plan h 0,068(2) A, dans lequel les longueurs des liaisons &B = 1,504(3) et 1,5 16(3), F-B = 1,358(3) et 1,359(3) A indiquent la prksence d'une faible liaison entre le coordinat et la portion FIB.

Mots cle's : composC organobork, structure cristalline, compose bore. [Traduit par la redaction]

Introduction The synthesis of the diphenylboron chelate 3 via condensa-

tion of salicylohydroxamic .acid, 1 , with cyclopentanone and subsequent reaction of the cyclocondensate 2 with oxybis- (diphenylborane) has been described in a previous report, along with the crystal and molecular structure of 3(1).

In the course of this investigation we were interested in the reactivity of 2 towards the stronger Lewis acid BF, and also in the possible structural differences between the expected difluoroboron chelate 6 and the diphenylboron analog 3. Thus we reacted 2 with boron trifluoride and obtained a crystalline product with the elemental analysis expected for the BF2 chelate 6. As for 3, infrared and 'H nrnr data did not allow the exclusion of isomeric structures like 5, 8 , 10, or 12, which, in part, have been discussed by analogy to the diphenylboron derivative 3. An X-ray crystallographic analysis was undertaken in order to provide unambiguous proof of the structure 6.

'Previous paper in this series: ref. 17.

We also prepared single crystals of the hydroxamic acid with the assumed 0,N-cycloacetal structure 2 in order to obtain data on the solid state structure of the free ligand. Formulae of the type 2 have generally been used for condensation products of salicylohydroxamic acid with aldehydes or ketones (2), but have never been proven. All subsequent reaction products, such as the chelates 3 and 6, could also be the result of a rearrangement of possible educts like 4, 7, 9, or 11 (which are isomers of 2) during the reaction with the Lewis acid boron compound.

The five-membered cyclic 0,O-acetal structure in 4 repre- sents the well-known (3) 1,4,2-dioxazole ring system that can also be synthesized by condensation of hydroxamic acids with different carbonyl compounds (3a, 3b, 3c, 3g). The six- and seven-membered cyclic 0,O-acetals, 7 and 9, have not been reported in the literature, to the best of our knowledge. The 2H-1,3-oxazet N-oxide moiety of 11 (and of 12) is an unknown type of heterocyclic N-oxide, and its formation seems unlikely under the applied reaction conditions. It is, however, reminis- cent of the homologous dihydrooxazole N-oxide ring fragment

Printed in Canada I lmprimd au Canada

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CAN. J. CHEM. VOL. 69. 1991

N' \ 0

BF3

7 8 8 - dimer

9 10 10 - dimer

of 13(4). For a definitive establishment of the hitherto postulated Experimental Structure 2, an X-ray analysis of this material has been per- 2 , 3 - D i h y d r o - 3 - h y d r o x y - 2 , 2 - t e ~ r a m e t h y ~ e n e z - - n , 2 formed. The compound was prepared according to our previous report (1).

A comparison of bond lengths in the free ligand 2 with those Crystals suitable for X-ray analysis were obtained by recrystallization in the chelates 3 and 6 should give some indication of the from benzene/petroleurn ether (2a) or methanol (26). influence of the different borenium ions, Ph2B+ and F2B+, on the bonding system of the hydroxamate and the 0,N-acetal functions in these molecules.

n

2,2-D~uoro-4,4-tetramethylene-l,3,5-trioxa-3a-azonia-2-borata- 2,3,4,5-tetrahydro-1H-cyclopenta[a]naphthalene, 6

2 (0.44 g, 2 mmol) was suspended in 30-50 rnL diethylether. After addition of diethyl ether-boron trifluoride (0.57 g , 4 mmol) the suspen- sion was refluxed for 30 min. The warm solution was filtered and the volume reduced by distillation of the solvent in vacuo, until only a few mL remained. Crystallization started during evaporation and was com- pleted at room temperature. Yield: 0.49 g (91%), mp 125°C (from ether). Anal. calcd. for Cl2HI2BF2NO3: C 53.97, H 4.53, N 5.24; found: C 54.03, H 4.60, N 5.22. Infrared (KBr): 1635 cm-I (C=O/C=N). 'H nmr (90 MHz, CDC13/TMS): 6 (ppm) = 1.68- 2.68 (m, -(CH2)4-), 6.94-7.78 (rn, C6H4).

Crystals suitable for X-ray analysis were obtained by recrystalliza- tion from absolute diethylether.

X-ray crystallographic atlalyses of 2 and 6 Two crystalline modifications of the free ligand 2, 2a and 2b, were

analyzed. Crystallographic data for the three structures appear in Table 1. The final unit-cell parameters were obtained by least-squares on the setting angles for 25 reflections with 20 = 35.9-40.2' for 2a, 16.2- 19.2" for 26, and 60.2-99.2' for 6. The intensities of three standard reflections, measured every 150 reflections throughout the data collec- tions, were essentially constant for all three compounds. The data were

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KLIEGEL ET AL.: 1

TABLE 1. Crystallographic data"

Compound 2a 2b 6 Formula C 1 2 ~ 1 3 ~ ~ 3 C I Z H I ~ N O ~ Cj2HI2BF2NO3 fw 219.24 219.24 267.04 Crystal size, mm 0.35 X 0.45 X 0.45 0.13 X 0.30 X 0.50 0.20 X 0.25 X 0.25 Crystal system Triclinic Monoclinic Monoclinic Space group p i C2/c p 2 1 /c a , 8, 8.551(1) 17.41(2) 5.354(1) b , A 9.331(3) 10.665(6) 17.654(2) c, 8, 7.236(1) 12.427(8) 12.844(1) a, deg 103.38(2) 90 90 I% deg 104.68(1) 1 15.74(5) 100.1 l(2) Y, deg 80.37(2) 90 90 v, A3 539.7(4) 2078(3) 1195.1(5) Z 2 8 4 ~ c a ~ c r g/cm3 1.35 1.40 1.48 F(000) 232 928 552 Radiation Mo Mo Cu k, cm-' 0.91 0.95 10.40 Transmission factors 0.917-1 .OO Scan type W-28 w-20 0-20 Scan range, deg in w 1.30 + 0.35 tan 0 1.25 + 0.35 tan 0 l .OO + 0.30 tan 0 Scan speed, deg/min 32 16 32 Data collected + h , * k , * I * h , + k , + I +h, + k , * I 20max, deg 55 55 150 Crystal decay Negligible Negligible Negligible Total no. of reflections 2627 2634 2739 No. of unique reflections 2475 2520 2468 Rmerge 0.028 0.074 0.017 No. of reflcns with I r 3u(I) 1712 1505 1675 No. of variables 198 198 223 R 0.046 0.046 0.041 R ,, 0.061 0.062 0.051 gof 2.25 1.88 2.37 Max A/u (final cycle) 0.01 0.01 0.09 Residual density e/A3 0.30 0.24 0.15

"Temperature 294 K, Rigaku AFC6S diffractometer, Mo K, (A = 0.71069 A) or Cu K, (A = 1.54178 A) radiation, graphite monochromator, takeoff angle 6.0°, aperture 6.0 X 6.0 mm at a distance of 285 mm from the crystal, stationary background counts at each end of the scan (scan/background time ratio 2: I) , up to eight rescans, 02(F') = [S'(C + 48) + (pF')']/Lp' (S = scan rate, C = scan count, B = normalized background count,p = 0.045 for 2a, 0.050 for 26, and 0.040 for 6 ) . function minimized Z,v(lF,I - IF,I)' where LV = 4FO2/u'(F,'), R = CIIF,( - IF,I/CIF,~, R,,. = (CW(F,~ - ~F,~'/CW~F,I')'/', and gof = [C(IF,I - JF,)'/(,~ - ,I)]'/'. Values given for R , R,,, and gof are based on those reflections with I ? 3a(I).

processed' and corrected for Lorentz and polarization effects, and in the case of 6, absorption (empirical, based on azimuthal scans for four reflections).

The structure analyses of both the triclinic and monoclinic forms of 2 were initiated in the centrosymmetric space groups PT and C2/c, respectively, on the basis of E-statistics, the choices being confirmed by subsequent calculations. The structures were solved by direct methods, the coordinates of the non-hydrogen atoms being determined from E-maps and subsequent difference Fourier syntheses. The cy- clopentane ring in compound 6 was found to be conformationally disordered. A twofold disordered model involving two ring carbon atoms was refined. Hydrogen atoms were refined with isotropic thermal parameters except for the disordered hydrog~n atoms in 6 which were fixed in idealized positions (dCuH = 0.98 A, BH = l.2Bbondcd Neutral atom scattering factors and anomalous dispersion corrections for the non-hydrogen atoms were taken from the International tables for X-ray crystallography (5). Final atomic coordinates and equivalent

'TEXSAN/TEXRAY structure analysis package which includes versions of the following: MITHRIL, integrated direct methods, by C. J. Gilmore; DIRDIF, direct methods for difference structures, by P. T. Beurskens; ORFLS, full-matrix least-squares, and ORFFE, func- tion and errors, by W. R. Busing, K. 0 . Martin, and H. A. Levy; ORTEP 11, illustrations, by C. K. Johnson.

isotropic thermal parameters, bond lengths, bond angles, and intra- annular torsion angles appear in Tables 2-5, respectively. Hydrogen atom parameters, anisotropic thermal parameters, bond lengths and angles involving hydrogen, general torsion angles, intermolecular con- tacts, least-squares planes, and measured and calculated structure fac- tor amplitudes for the three structures are included as supplementary material.

Results and discussion The condensation product of salicylohydroxamic acid with

cyclopentanone has the cyclic 0,N-acetal structure 2 (Fig. I ) and belongs to the class of intramolecular N-alkylated cyclic hydroxamic acids (6). There is little structural information on this type of ligand in the literature. Besides an ORTEP diagram of 5-methoxy-6-methyl- I-hydroxy-2(lH)-pyridinone without further structural data (7) and some calculated bond lengths for 1-hydroxy-2(lH)-pyridinone (8), the only complete crystallog-

3Supplementary material mentioned in the text may be purchased from the Depository of Unpublished Data, Document Delivery, CISTI, National Research Council of Canada, Ottawa, Ont., Canada KlAOS2.

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676 CAN. 1. CHEM. VOL. 69, 1991

TABLE 2. Final atomic coordinates (fractional) and Beq (A2)*

Atom x Y z Be,

TABLE 3. Bond lengths (A) with estimated standard deviations

2a

*Be, = (8/3).rr2CCU,jai*a,*(ni.aj) +Site occupancy 0.50.

Atom Atom

O(1) C(8) O(1) C(1) O(2) N O(3) c(2) N c(2) N c(1) C(1) C(9) C(1) C(2) C(3)

Distance Atom Atom

C(3) C(3) C(4) C(5) C(6) C(7) C(9) C(9) C(10) C(1OA) (311) C(l IA)

C(8) C(4) C(5) C(6) C(7) C(8) C(I OA) C(10) C(11) C(11A) C(12) C(12)

Distance

1.389(3) 1.392(2) 1.374(3) 1.388(3) 1.376(3) 1.386(2) 1.5 12(3) 1.5 12(4) 1.528(3)

raphic characterization of a 1-hydroxy-2-pyridinone derivative is that reported (9) for compound 14.

Both crystal forms of the free hydroxamic acid 2 contain centrosyrnmetric 0-H...O hydrogen-bonded dimers (2a: 0(2&H(1)...0(3)(-0x, 1 - y, 1 - z), O..-H = 1.72(2) A, O...O = 2.633(2) A, O--H...O = 168(2)"; 2b: O(2)- H(1)...0(3)(2 - x, - y, - 1 - z), 0.e.H = 1.80(3) A, 0...0 = 2.682(3) A, O--H-a.0 = 164(3)"). Similar hydrogen-bonded dimers are present in the solid-state structure of free salicylohy- droxamic acid (10). This is in contrast to the intramolecular hydrogen bond in 14, the "chelated proton" being located from a difference Fourier synthesis (9). Nevertheless, an intramolecu- lar hydrogen bond can be expected for compound 2 in non-polar solvents or in the gas phase, and is indirectly demonstrated by the replacement of the chelated proton by the borenium ions Ph2B+ (in compound 3) or F2B+ (in compound 6). Apart from the above-mentioned hydrogen bonds, all other intermolecular distances in both 2a and 2b correspond to normal van der Waals interactions.

The average C(2)--0 and S(2)-N distances in the cyclocon- densate 2 (1.235 and 1.346 A) are shorter and longer, respec; tively, than the corresponding values of 1.258 and 1.3 16 A reported for salicylohydroxamic acid 1 (10). There is more

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KLIEGEL ET AL.: 1

TABLE 4. Bond angles (deg) with estimated standard deviations

Atom Atom Atom Angle Atom Atom Atom Angle

withdrawal of electron density from the carbonyl group of salicylohydroxamic acid 1, which is involved in a bifurcated hydrogen bond with an N-hydroxy group and the free phenolic OH group of neighboring molecules (10). The phenol function of 2 is blocked by 0,N-acetalization and has no proton available for participation in intermolecular hydrogen-bonding. Thus the carbonyl group of 2 takes part in only one hydrogen bond to the hydroxamic acid group of a neighboring molecule, and retains

more of its double bond character. The partial loss of double bond character of the carbonyl group in 1, caused by donating into the bifurcated intermolecular hydrogen-bonding system present in crystalline 1, should be even more pronounced in the boron chelates 3 and 6 which employ the carbonyl group as ligand for the electron-deficient borenium ions. Indeed, the lengthened C=O bonds of 3 and 6, and the correspondingly shortened (carbony1)C-N distances, suggest an increased elec-

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CAN. J. CHEM. VOL. 69, 1991

FIG. 1 . Stereoviews of triclinic (top) and monoclinic 2 (middle) and 6 (bottom); 50% probability thermal ellipsoids are shown for the non-hydrogen atoms.

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TABLE 5. Intra-annular torsion angles

Atoms Value

2a (left) and 2b (right)

O(ltC(l)--N - c ( 2 ) -44.9(2) C(1)-N 4 ( 2 ) 4 ( 3 ) 17.8(2) N - C ( 2 ) 4 ( 3 ) 4 ( 8 ) 8.0(2) C(a-C(3)4(8)*(1) -3.0(2) c ( 3 k C ( 8 ) 4 ( 1 I<( 1) - 27.4(2) C(8+0(1)4(1)-N 47.6(2)

C(12)-C(1)-C(9)4(10) -36.8(2) c(l - ( 9 ) 4 ( 1 0 ) 4 ( 1 1 ) 30.8(2) C(9W(lO)-C(ll+C(l2) - 13.2(3) C(l0)-C(l l+C(12&C(1) -9.5(2) C(l lw(12)-C(1)-C(9) 28.5(2)

*Values for the two conformations of the disordered cyclopentane ring are given, those involving atoms C(1OA) and C(I1A) are on the right.

tron withdrawal out of the amide function accompanied by a more pronounced lone pair delocalization from the nitrogen atom towards the carbonyl group. The relatively small differ- ences between the C=O and C-N bond distances in the boron chelates 3 and 6 reflect the higher Lewis acidity of the chelated borenium ion F2B+ in 6 relative to that of Ph2B+ in 3. The C 4 bond lengths inccease from an averaFe of 1.235 A in 2, 1.258 in 1 (lo), 1.288 A in 3 (I) , to 1.295 A in 6 while the amide C 4 bond lengths decrease correspondingly: 1.346 (average), 1 .3 16, 1.309, 1.294 A. The IT-bond-orders of the C=O and C-N bonds have been estimated from plots of bond length vs. IT-bond order (1 1): the C-0 IT-bond orders are 0.83, 0.70, 0.57, and 0.54 for 2, 1, 3, and 6, respectively, and the C-N IT-bond orders are 0.53, 0.67, 0.72, and 0.79 for 2, 1, 3, and 6, respectively.

There is not much change in the bond lengths of the 0 ,N- acetal grouping of the ligand 2 upon formation of the chelates 3 or 6. The six-membered 1,3-oxazine heterocycle in the chelates 3 (1) and 6 have distorted "envelope" conformations. Compared to the less rigid tetrahydro-l,3-oxazin-4-one ring in compound 15 (12), the "semiplanar" skeleton of the dihydro-1,3-oxazin-4- one moiety in 2 shows slightly elongated bonds in the sterically less strained 0,N-acetal fragment. Th; average C(1)-0 and C(1)-N distances of 1.433 and 1.474 A are slightly l o n ~ e r than the corresponding bond lengths of 1.417 and 1.469 A in the saturated bicyclic system of 15 (12).

As discussed previously for the diphenylboron chelate 3 (1) an enhanced IT-interaction between the hydroxamate system and the adjacent aryl group upon chelation can be observed by the shortening of the C(carbonyl)-C(aryl) ban< of the ligand. The average C(2)-C(3) distance in 2 is 1.475 A while the corres- ponding bond lengths in the diphenylboron ccelate 3 and the difluoroboron chelate 6 are 1.438 and 1.436 A, respectively. The B-0 bonds of the difluoroborn chela t~ 6 (1.504 and 1.5 16 A) are shorter by an average of 0.06 A dhan those in the diphenylboron chelate 3 (1.558 and 1.578 A) (I) . This differ- ence is similar to that observed for the difluoro- and diphenyl- lboron chelates of N-methylacetohydroxamic acid (13, 14): about 0.05 A. The mean F-B/mean 0-B bond length ratio of 0.900 for 6 represents the weakest overall binding strength of the 0,O-chelating ligand with respect to the "F2B+" moiety yet noted for a compound of this type having a five-membered chelate ring. These ratios range from 0.920 to 0.961 (mean 0.947) for other "F2BO2" compounds having five-membered chelate rings (1 3, 15, 16). The five-membered OBONC chelate ring in 6 has a flattened B-envelope conformation (Table 5) and is, in fact, planar to within 0.068(2) A. The most significant intermolecular contact in the solid state structure of 6 corres- ponds to a weak C-H...O interaction: C(4)-H(l).-.0(:)(1 - x , l - y , l - z ) , H...O = 2.45(3), C.e.0 = 3.363(3) A, and C-H...O = 151(2)".

The free ligand, cyclic hydroxamic acid 2, possesses a dis- tinctly shorter C(2)-N amide bond (avera e 1.346 A) than does g the cyclic hydroxamic acid 14 (1.388 ) which also has a six-membered ring skeleton (9). The difference between the C = O bonds inothese two coypounds is not very significant: average 1.235 A in 2, 1.24 1 A in 14. The N+ distance in 2 (average 1.398 A) is longer by about 0.01 A than that in 14 (1.387 A) (9).

Acknowledgements We thank the Natural Sciences and Engineering Research

Council of Canada and the Fonds der Chemischen Industrie, Frankfurt am Main, for financial support.

1. W. KLIEGEL, M. TAJERBASHI, S. J. RETTIG, and J. TROTTER. Can. J. Chem. 68,69 (1990).

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3. (a) 0 . EXNER. Coll. Czechoslov. Chem. Commun. 21, 1500 (1956); (b) E. SCHMITZ and S. SCHRAMM. Chem. Ber. 100,2593 (1967); (c) H. NOHIRA, K. INOUE, H. HATTORI. T. OKAWA, and T. MUKAYAMA. Bull. Chem. Soc. Jpn. 40, 664 (1967); (4 S. MORROCCHI, A. QUILICO, A. RICCA, and A. SELVA. Gazz. Chirn. Ital. 98, 891 (1968); ( e ) R. HUISGEN and W. MACK. Chem. Ber. 105,2805 (1972); (f) N. V. VASIL'EV, S. A. KHOKHLOVA, A. F. KOLOMIETS, and A. G. SOKOL'SKII. Zh. Org. Khim. 20, 1983 (1984) (J. Org. Chem. USSR 20, 1364 (1984)); (g) D. GEFFKEN. Arch. Pharm. (Weinheim) 318, 895 (1985); ( h ) E. J. BREAUX. J. Heterocycl. Chem. 23, 463 (1986); (i) D. MACKAY, E. G. NEELAND, and N. J. TAYLOR. J. Org. Chem. 51,235 1 (1986).

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5. International tables for X-ray crystallography. Kynoch Press: Birmingham, U.K. (present distributor Kluwer Academic Pub- lishers: Dordrecht, The Netherlands), Vol. IV. 1974. pp. 99-102 and 149.

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