Ethers such as the title compound, C~HIINO3S, (1), rearrange thermally to give N-allyl isomers, (2), in high yield. The X-ray structure determination of the title ether shows a central C--O--C linkage which has one very short (notional) C--O single bond and one exceptionally long single C--O bond. The thermal migration of allyl from the O to the N atom involves the breaking of one of the ether bonds in (1) and a shortening of the other as it becomes a formal carbonyl group in the product (2). The rearrangement is thus considerably assisted by the ground-state structure of the starting ether, in which the bond to be broken is already stretched and the one
that is to form a carbonyl group is already a substantial partial double bond

Barkley, J. V.

Cristiano, Maria Lurdes Santos

Johnstone, Robert A. W.

Loureiro, Rui M. S.

Acta Crystallographica Section C Crystal Structure Communications

Sapientia

JAI-NHUKNAN, KARIPIDES, HUGHES AND CANTRELL 383 The help of Professor John M. Hughes, Department ofGeology, Miami University, Oxford, USA, is gratefully acknowledged. Lists of atomic coordinates, displacement parameters, structure factors and complete geometry have been deposited with the IUCr (Reference: BKI164). Copies may be obtained through The Managing Editor, International Union of Crystallography, 5 Abbey Square, Chester CH i 2HU, England. References Enraf-Nonius (1985). Structure Determination Package. SDP/PDP User's Guide. Version 3.0. Enraf-Nonius, Delft, The Netherlands. Enraf-Nonius (1989). CAD-4 Software. Version 5.0. Enraf-Nonius, Delft, The Netherlands. North, A. C. T., Phillips, D. C. & Mathews, E S. (1968). Acta Co'st. A24, 351-359. Sheldrick, G. M. (1990). Acta Cryst. A46, 467-473. Sheldrick, G. M. (1993). SHELXL93. Program for the Refinement ofCrystal Structures. University of Gottingen, Germany. Zsolnai, L. (1995). XPMA and ZORTEP. Interactive Graphics Pro- grams. University of Heidelberg, Germany. Acta Cryst. (1997). C53, 383-386 3- (E)-But-2-enoxy- 1,2-benzisothiazole 1,1-Dioxide: Unusual C--OmC Ether Bond Lengths and Reactivity JAMES V. BARKLEY, a M. LURDES S. CRISTIANO, b ROBERT A. W. JOHNSTONE a AND RUI M. S. LOUREIRO b ~Department of Chemistry, University of Liverpool, Liverpool L69 3BX, England, and b UCEH, Campus de Gambelas, Universidade do Algarve, 8000 Faro, Portugal. E-mail: rjO5 @ liverpool.ac.uk (Received 5 July 1996; accepted 12 November 1996) Abstract Ethers such as the title compound, C~HIINO3S, (1), rearrange thermally to give N-allyl isomers, (2), in high yield. The X-ray structure determination f the title ether shows a central C - -O- -C  linkage which has one very short (notional) C--O single bond and one exceptionally long single C--O bond. The thermal migration of allyl from the O to the N atom involves the breaking of one of the ether bonds in (1) and a shortening of the other as it becomes a formal carbonyl group in the product (2). The rearrangement is thus considerably assisted by the ground-state structure of the starting ether, in which the bond to be broken is already stretched and the one that is to form a carbonyl group is already a substantial partial double bond. © 1997 International Union of Crystallography Printed in Great Britain - all rights reserved Comment Compounds bearing an allylic alcohol function are often vital structural units of biologically active systems. In addition, allylic alcohols have attracted widespread attention as key intermediates for the synthesis of various types of compounds (Kumar & Dittmer, 1994; Adam, Peters & Renz, 1994; Evans, Holmes & Russell, 1994; Bergmeier & Stanchina, 1995; Fujii, Habashita, Akaji, Nakai, Ibuka, Fujiwara, Tamamura & Yamamoto, 1996). The title compound, (1), can be prepared readily from 3-chloro-l,2-benzisothiazole 1,1-dioxide (pseudosacch- aryl chloride) and crotyl alcohol in the presence of base. It undergoes easy thermal rearrangement to the N-allyl isomer [(2); see scheme below]. Formally, this [3,3] re- arrangement is similar to that reported for 5-allyloxy-1- phenyltetrazoles (Cristiano, 1994; Cristiano, Johnstone & Price, 1996). Under some conditions, [1,3] migration may also occur. Recent investigations concerning the structure and reactivity of aryloxytetrazoles and aryl- oxypseudosaccharins towards catalytic hydrogenolysis and cross-coupling have shown that much of the re- activity of these ethers can be ascribed to unusual bond lengths in the central C - -O- -C  ether bonds caused by a usually powerful electronegative effect from the tetra- zole or pseudosaccharyl ring system (Brigas & John- stone, 1996; Alves, Brigas & Johnstone, 1996; Alves, 1996). For example, aryloxypseudosaccharins (3-aryl- oxy- 1,2-benzisothiazole 1,1-dioxides) are characterized by having art ether linkage in which one CmO bond is long and the other is short. The effect of the benziso- thiazole 1,1-dioxide ring system is to lengthen the aryl C--O bond from a typical value of 1.36 A in a phenol to about 1.44 ,~, in the ether. At the same time, the link from the ether oxygen to the pseudosaccharyl system is very short (1.32 A) for a C--O single bond, viz. it is a partial double bond. The net result of these electronic changes on converting a phenol into its pseudosacch- aryl ether is to provide a molecular structure that lies close to the supposed transition-state structure for the migration shown below, in which an originally strong phenolic C--O bond becomes easily cleavable catalyti- cally in the ether. (1) (2) Because of the ease of rearrangement of allyloxy- pseudosaccharins such as compound (1) (see scheme above), it was of interest to discover whether or not the electronegative pseudosaccharyl s stem was exerting a strong electronic influence on the allyloxy group, Acta Co'stallographica Section C ISSN 0108-2701 © 1997 384 CllHliNO3S thereby making the rearrangement easier than it would be without its influence. There are two molecules in the asymmetric unit of (1) (Fig. 1). Except where otherwise stated, the following discussion concerns one of these molecules [C(1)--C(11)]. As with the aryloxypseudosaccharins, the C--O bonds in the central C--O---C ether linkage of the title compound are unequal in length. Compared with aryloxypseudosaccharins, allyloxypseudosaccharin (1) possesses a central C---O----C linkage in which one C---O bond is shorter [1.314 (7) versus  1.32-1.34 ,~,] and one that is much longer [1.488 (7) versus  1.42-1.44 A] than normal values. Indeed, the long single C---O bond in ether (1) is significantly longer than even a normal aliphatic C--O single bond, which is typically 1.43 A, (Handbook of Chemistry and Physics, 1993-94), and has a bond order (Pauling, 1947, 1960) of only 0.9. Similarly, the short C---O bond to the pseudosaccharyl ring has a partial double-bond character of 1.59. 0 C(16) ~. .~C(15)  0(4) (~) N(2) ~C(22)X  C(19) O(5 )~llPi O~ 6C(21 ,0(2)/~O(3) C(I 1)~C!0~C) C(1) ai~t,, k_: ~ o(1) fL~ C(2) C(4~@~-~ (3, c((~O Fig. I. A perspective iew of the two independent molecules of the title compound showing 50% probability displacement ellipsoids. The atomic numbering system does not follow normal rules of chemical nomenclature. H atoms have been assigned arbitrary radii. The powerful electronegative effect of the pseudo- saccharyl group extends even into the allyl group itself. The single C(2)--C(3) bond of the aUyl group is thus shorter at 1.477(9)A than a 'standard' single bond (1.53 ~,; Allen, Kennard, Watson, Brammer, Orpen & Taylor, 1987; Handbook of Chemistry and Physics, 1993-94). The C.(3)--C(4) double bond is slightly shorter [1.278(9)A] than that of a 'standard' double bond (1.29 A). As well as the strong conjugation between the ether oxygen and the pseudosaccharyl ring system, evident from the very short C--O bond length, the ether C--O---C bond angle is close to 116 °, indicating a considerable degree of sp 2 character at the O atom. This is again similar to the corresponding linkage in aryl- oxypseudosaccharins (Brigas & Johnstone, 1996; Alves, Brigas & Johnstone, 1996). Furthermore, the torsion angle N(1)--C(1)--O(1)--C(2) is 0.0 (8) °, consistent with sp 2 hybridization at the oxygen and the consequent drive for maximum overlap between the p orbital on oxygen and the 7r system in the pseudosaccharin ri gs. In a further interesting comparison with some 70 diaryl ethers, aryl tetrazolyl ethers and aryl pseudosaccharyl ethers, for which the sum of the two C--O bond lengths of the ether linkages is 2.78+0.02,4, (Alves, 1996), the corresponding sum for compound (1) is very similar at 2.803 (13) A. The rearrangement of the allyloxy compound (1) to its N-allyl isomer [(2); see scheme above] in which an N--C bond is formed [c in structure (3)] requires that the short ether C--O bond [a in structure (3)] should shorten more as it moves towards being a C---O double bond and that the long C--O bond [b in structure (3)] should stretch more as it breaks. The structure of the starting allyloxypseudosaccharin (1) is thus geometri- cally well advanced along the reaction coordinate and must be quite similar to the likely structure of the tran- sition state. The proximity of the transition state and starting structures implies an early transition state, with a small activation energy of reaction (Leffler, 1953; Hammond, 1955). It has been pointed out that bond distance and energy are particularly important because they provide good reasons for the sensitivity of the ac- tivation energy of bond breaking to small changes in ground-state geometry (Btirgi & Dunitz, 1987). The mi- gration is thus made easier than it would have been if there had been no inequality in the C--O bonds of the central ether linkage. This structure determination provides at least a partial explanation for the ease of rearrangement observed in the reaction scheme above. 1~,~ s,N "c" < O 2 (3) If the two independent molecules in the asymmetric unit are compared, it is found that for their benzisothia- zole 1, l-dioxide sections and for the central C - -O- -  BARKLEY, CRISTIANO, JOHNSTONE AND LOUREIRO 385 C bonds, the bond lengths and angles are very similar within error limits and the above discussion is applicable to either molecule. In contrast, comparison of the C2- -  C3 and C4 C5 bond lengths in the allylic section of one molecule with the corresponding C13---C14 and C I~ C15 lengths in the other shows that for these specific bonds there are significant differences; C2- -C3  is 0.032 (12),4, longer than C13----C14, and C4---C5 is 0.058 (13)A shorter than C14- -C15.  Efforts are being made to determine whether or not these two differences are real or perhaps due to random noise in the data, even though all other lengths and angles are consistent between the two molecules. Experimental 3-Chloro-l,2-benzisothiazole 1,1-dioxide (pseudosaccharyl chloride; 2.71 g, 13.46 mmol) was added to a mixture of (E)- but-2-enol (crotyl alcohol; 1.25 ml, 1.06 g, 14.7 mmol) and triethylamine (5 ml) in toluene (30m 1). The solution was stirred at 313 K until all of the starting material had dis- appeared (TLC; about 1 h). The precipitate of triethylamine hydrochloride was filtered off and the filtrate was evaporated to give a yellow solid, which was recrystallized from ethanol (2.2 g, 69.1% yield; m.p. 397-398 K). Analysis: found C 55.6, H 4.7, N 5.9%; Cl iHt tNO3S requires C 55.7, H 4.7, N 5.9%. t H NMR (CDC13): 6 1.75 (3H, d, J = 5.7 Hz), 4.95 (2H, d, J = 6.7 Hz), 5.8 (1H, m), 6.0 (1H, m), 7.73 (3H, m), 7.88 (1H, d, J = 6 Hz). Crystal data CliHllNO3S Mo Ko~ radiation Mr = 237.27 A = 0.71073 ,~, Monoclinic Cell parameters from 25 P21/ n reflections a = 8.145 (4) ,~ 0 - 3.7-6.7 °b = 16.375 (5) ,4, # = 0.259 mm-J c = 17.274 (4)/~, T = 153 K /3 = 92.26 (3) ° Needle V = 2302 (1) ,~3 0.40 × 0.15 x 0.15 mm Z = 8 Colourless Dx = 1.369 Mg m -3 Dm not measured Data collection Rigaku AFC-6S diffractom- eter w/20 scans Absorption correction: none 4168 measured reflections 3855 independent reflections 2048 reflections with I > 3o'(/) Rint = 0.03311 0max = 25 ° h = 0 ---~ 10 k = 0 ---~ 19 l = -21  ~ 21 3 standard reflections every 150 reflections intensity decay: 0.10% Refinement Refinement on F R = 0.0569 wR = 0.0623 S = 1.810 (/X/o.)m,,,x = 0.0585 Apmax = 0.48 e A, -3 Apmin = -0.36 e/~-3 Extinction correction: none 2048 reflections Scattering factors from 199 parameters International Tables for H atoms: see below Crystallography (Vol. C) w = l/[o.2(Fo) + 0.000221Fol21 Table 1. Selected geometric parameters (A, °) O(I)--C(I) 1.314 (7) C(3k--C(4) 1.278 (9) 0( I )~(2)  1.488 (7) C(4k--C(5) 1.51 (I) O(4)---C(I 2) 1.317 (7) C(13)----C(14) 1.445 (9) O(4)---C(I 3) 1.483 (8) C(14)---C(15) 1.336 (9) C(2)--C(3) 1.477(9) C(I 5)~C(16) 1.52(1) C( 1 )---O( 1 )----C(2) 115.9 (4) C(3 ?---C(4)--C(5) 125.8 (7) C( 12)---O(4)---C(13) 117.4(4) O(4)---C(13)--C(14) 110.3(5) O( 1 )--C(2)---C(3) 107.1 (5) C(I 3)--C(14)---C(15) 119.3(7) C(2)----C(3)--C(4) 122.0(7) C( 14)--C( 15)---C(16) 123.3(7) N( 1 )--C(I )---O( I )--~(2) 0.0 (8) N(2)--C(12)--O(4)--C(13) - 1.3 (8) C( I )--O( 1 )--C(2)--C(3) 174.1 (5) C(2)---O( I )--C( 1 )--C(6) 179.7 (5) C( 12)---O(4)---C( 13)---C(14) 85. I (6) C( 13)--O(4)--C( 12)--C(17) 178.1 (5) H atoms were included in calculated positions and allowed to ride with C--H = 0.95 ~, and Ui~o(H) = 1.2U~q(C). Data collection: MSCIAFC Diffractometer Control Software (Molecular Structure Corporation, 1988). Cell refinement: MSCIAFC Diffractometer Control Software. Data reduction: TEXSAN PROCESS (Molecular Structure Corporation, 1995). Program(s) used to refine structure: TEXSAN. Software used to prepare material for publication: TEXSAN. The authors thank Dr Alexander J. Blake for perspi- cacious comments on the alkene bond lengths, one of the referees for his cautionary remarks on the effects of random noise in the data and Dr Marjorie M. Harding for her encouragement. The authors also gratefully acknowledge generous financial assistance from JNICT (Portugal) and the Eschenmoser Trust (UK). Lists of atomic coordinates, displacement parameters, tructure factors and complete geometry have been deposited with the IUCr (Reference: BMII04). Copies may be obtained through The Managing Editor, International Union of Crystallography, 5 Abbey Square, Chester CH 1 2HU, England. References Adam, W., Peters, K. & Renz, M. (1994). Angew. Chem. Int. Ed. Engl. 33, I 107- I 108. Allen, F. H., Kennard, O., Watson, D. G., Brammer, L., Orpen, A. G. & Taylor, R. (1987). J. Chem. Soc. Perkin Trans. 2, pp. SI-S!9.  Alves, J. A. C. (1996). PhD thesis, University of Liverpool, England. Alves, J. A. C., Brigas, A. F. & Johnstone, R. A. W. (1996). Acta Cryst. C52, 1576-1578. Bergmeier, S. C. & Stanchina, D. M. (1995). Tetrahedron Len. 36, 4533--4536. Brigas, A. F. & Johnstone, R. A. W. (1996). Acta Cryst. C52, 1293- 1296. Btirgi, H.-B. & Dunitz, J. D. (1987). J. Am. Chem. Soc. 109, 2924- 2926. Cristiano, M. L. S. (1994). PhD thesis, University of Liverpool, England. Cristiano, M. L. S., Johnstone, R. A. W. & Price, P. J. (1996). J. Chem. Soc. Perkin Trans. In the press. 386 CI1HI1NO3S Evans, P. A., Holmes, A. B. & Russell, K. (1994). J. Chem. Soc. Perkin Trans. 1, pp. 3397-3409. Fujii, N., Habashita, H., Akaji, M., Nakai, K., Ibuka, T., Fujiwara, M., Tamamura, H. & Yamamoto, Y. (1996). J. Chem. Soc. Perkin Trans. 1, pp. 865-866. Hammond, G. S. (1955). J. Am. Chem. Soc. 77, 334-338. O Handbook of Chemistry & Physics (1993-94). Edited by D. R. Lide, ~,,-~',,,~OCOMe pp. 9-1 to 9-41. Boca Raton: CRC Press. I~ I1 I[ Kumar, A. & Dittmer, D. C. (1994). J. Org. Chem. 59, 4760-4764. ~ C 1  Leffler, J. E. (1953). Science, 117, 340-341. O Molecular Structure Corporation (1988). MSC/AFC Diffractometer (2) Control Software. MSC, 3200 Research Forest Drive, The Wood- lands, TX 77381, USA. Molecular Structure Corporation (1995). TEXSAN. Single Co'stal Structure Analysis Software. Version 1.7. MSC, 3200 Research O I I  Forest Drive, The Woodlands, TX 77381, USA. Pauling, L. (1947). J. Am. Chem. Soc. 69, 542-553. ~ C I  Pauling, L. (1960). The Nature of the Chemical Bond, p. 239. Ithaca: Cornell University Press. O (4) orientation with respect to the chloro group as for ad- ditions involving monochloro quinones, e.g. compound (4) (see Scheme II) (Cameron, Feutrill & Keep, 1989). O OCOMe "~ OSiMe3 benzene @ OSiMe3 room • ~" temperature OMe O -" OMe (3) (1) Scheme I O /~]IOR ~ O R  OR' 0 OR' Scheme I1 Acta Cryst. (1997). C53, 386-387 ( l c~,4a /~,9a /3) -4a -Acetoxy-9a-ch lo ro -1 -  methoxy-3 - t r imethy ls i loxy - l ,4 ,4a ,9 ,9a ,10-  hexahydroanthracene-9 ,10-d ione  JONATHAN M. WHITE, ANDREW G. RICHES, DONALD W. CAMERON AND PETER G. GRIFFITHS School of  Chemistry, University of  Melbourne, Parkville, Victoria 3052, Australia. E-mail: jonathan_white@muwa)f unimelb, edu.au (Received 2August 1996; accepted 31 October 1996) Abstract The structure of the title compound, (lo~,4a/3,9a/3)-9a- chloro- 1-methoxy-9,10-dioxo-3-trimethylsiloxy- 1,4,4a,9,- 9a,10-hexahydro-4a-anthracenyl acetate, C20H23C106Si, was determined in order to ascertain the regiochemistry of the Diels-Alder reaction between acetoxychloro- naphthoquinone and a 1,3-dioxybutadiene. Comment The title compound, (1), was the sole product obtained from the Diels-Alder cycloaddition reaction between acetoxychloronaphthoquinone (2) (Fries & Ochwat, 1923) and 1-methoxy-3-(trimethylsilyloxy)butadiene, (3) (Scheme I). The present structure analysis estab- lishes that the regiochemistry of cycloaddition is such that the nucleophilic methylene terminus of the diene has attacked ipso to the acetoxy group; this is the same Compound (1) is a linear tricycle with a cis junc- tion between rings A and B. Both rings A and B exist in slightly distorted half-chair conformations with ap- proximate local axes of symmetry bisecting the C1- -  C6 and C3--C4 bonds for ring A, and the C1--C6 and C8--C13 bonds for ring B. The methoxy sub- stituent occupies a pseudo-axial position [O6---C5-- C4- -C3  -98 .7  (5) °] and is antiperiplanar to the chloro substituent [O6- - -C5- -C6- -C1  - 163.6 (3) ° ]. The chloro substituent is pseudo-equatorial with respect to ring B and pseudo-axial with respect to ring A, while the ace- toxy substituent is pseudo-axial with respect to ring B and pseudo-equatorial with respect to ring A. O1 C2 05 tqF'~ CI C1 04 C12 l~" - "  ,,"~N C 7 C3 06 02 i l~  C9 IC10 IC17 IC4 C5 ~,C20 Fig. 1. ZORTEP (Zsolnai, 1994) diagram of (1). Displacement ellipsoids are plotted at the 30~ probability level. © 1997 International Union of Crystallography Printed in Great Britain - all rights reserved Acta Ci3'stallographica Section C 1SSN0108-2701 ©1997 

3-( E )-But-2-enoxy-1,2-benzisothiazole 1,1-dioxide: unusual C—O—C ether bond lengths and reactivity

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