829

Reference Data

Table 1. (contd). Fyrroie ring

Corn- C-2 C-3 2 4 0 pound C-4 C-5

27 118.5 121.8 161.0

28 121.6 122.8 161.0

29 117.9 124.4 160.6

30 120.0 124.7 165.5

31 118.1 126.4 165.7

32 120.Zb 125.4 165.8

123.0 136.3

110.7 135.2

112.4 139.3

116.7 130.2

120.6 134.4

120.4b 134.3

R'

CH3 CH,

51.8

51.8

52.2

37.0

37.0

37.0

- R* R3 R4

C - i C - m

136.3 128.3 136.5 128.2 135.gb 1 28.0b

c - 0 c - P

128.9 126.1 129.9 126.1 128.8 126.0

CH3 co

52.0 166.5 52.2

164.4 52.6

166.3

C - i C - o CH3 CH, C - m c - p co

133.8 128.2 129.3 126.9

13.1 60.3

23.0 22.4 29.0 25.7

163.4

135.6b 127.8b 130.5 125.6

CH, CH3 C - i C - o

19.2 13.9

C - m c - p

130.5 125.1 129.0 128.3

14.2

23.7 22.8 32.9 27.4 19.4 13.9

'The positions of the chemical shifts in the table match those of the carbon atoms at the head of a column. Assignments with similar chemical shifts may be interchanged. Fourth signal not resolved. Signals superimposed.

References

1. R. J. Abraham, R. D. Lapper, K. M. Smith and J. F. Unsworth, J. Chem. SOC., Perkin Trans. 2 1004 (1974).

2. For examples see (a) R. J. Cushley, R. J. Sykes, C. K. Shaw and H. H. Wasserman, Can. J. Chem. 53, 148 (1975); (b) M. I. Struchkova, G. G. Dvoryantseva and R. P. Evstigneeva, Khim. Geterotsikl. Soedin. 485 (1979); (c) M. V. Sigalov, B. A. Trofimov, A. 1. Mikhaleva and G. A. Kalabin, Tetrahedron 37, 3051 (1981); (d) L. Lamartina, 0. Migliara and V. Sprio, J. Heterocycl. Chem. 19, 1381 (1982); (e) D. 0. A. Garrido, G. Buldain and B. Frydman, J. Org. Chem. 49,2619 (1984).

3. For examples see (a) L. L. Martin, C. J. Chang, H. G. Floss, J. A. Mabe, E. W. Hagaman and E. Wenkert, J. Am. Chem. SOC. 94, 8942 (1972); (b) G. Dana, 0. Convert, J. P. Girault

uC NMR Spectra of Substituted Indoles

GERARD0 BURTON (to whom correspondence should be addressed), ALBERT0 A. GHINI and EDUARDO G . GROS

Departamento de Quimica 0rg;inica and UMYMFOR, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, PabelMn 2, Ciudad Universitaria, 1428 Buenos Aires, Argentina

13C chemical shifts for indole and ten indoles substituted at positions 1, 3 and/or 6 are reported. Previous assignments have been revised using specific deuterium labelling and selective proton decoupling.

KEY WORDS Indole indole derivatives I3C NMR spectra

INTRODUCTION

In connection with our studies on the degradation of gramine in Hordeum uulgare plants,' we required 13C NMR data for several

4.

5.

6.

and E. Mulliez, Can. J. Chem. 54, 1827 (1976); (c) B. A. Trofimov, M. V. Sigalov, V. M. Bzhesovsky, G. A. Kalabin, S. E. Korostova, A. I. Mikhaleva and L. N. Balabanova, Khim. Geterotsikl. Soedin. 768 (1978); (d) M. M. Ito, Y. Nomura, Y. Takeuchi and S. Tomada, Bull. Chem. SOC. Jpn. 56, 533 (1983). K. W. Law, T. F. Lai, M. P. Sammes, A. R. Katritzky and T. C.

0. Attanasi, S. Santeusanio, G. Barbarella and V. Tugnoli,

P. Cabildo, R. M. Claramunt and J. Elguero, Org. Magn.

W. Mak, J. Chem. SOC., Perkin Trans. 7 1 11 (1984).

Magn. Reson. Chem. 23,383 (1985).

Reson. 22,603 (1984).

Received 27 January 1986; accepted 19 March 1986

plausible metabolites of this alkaloid for the identification of compounds isolated from in uiuo experiments when using l3C-labelled precursors. The resonance assignments of C-5 and C-6 of indole'-' have not been definitely established, and neither have those of many indole derivatives.

We report here that unambiguous assignments of the resonances of carbons 4, 5 and 6 of a series of indole derivatives can be carried out by specific deuterium labelling and selective proton decoupling.

RESULTS AND DISCUSSION

The indoles studied are listed in Table 1 and the corresponding I3C chemical shifts in Table 2. As there was a doubt about the original assignments of C-5 and C-6 of indole: we recorded the spectra of 6-d-indole (1, R, = 'H) and 6-d-gramine (5 , R, = 'H). The results indicated that the assignments should be reversed in both compounds with respect to those given in Refs 3-5, the chemical shifts of C-5 and C-6 being fairly constant for the series 1, 2, 3, 5, 6 and 11. The spectrum of 6-d-indole-3-carboxaldehyde (7, R, = 'H) showed that the assignments of C-4 and C-6 were reversed with respect to those given in Refs 3-5. Differentiation between the resonances of C-4 and C-5 in this compound was possible by selective irradiation of H-4 at 8.24ppm; this showed the line at

Reference Data

Table 1. Indole derivatives studied A

~ ~ ~ R 2 ./9 2

R3 7

Compound R l

1 H 2 H 3 H 4 H 5 H 6 H 7 H 8 H 9 H

10 H 11 Si(CH,),

R7.

H CH,NH,

CHZNHCH, CH=NCH, CH,N(CH,),

CH,OH CHO CO,H

H CHZN(CHJ2

H

R3

H H H H H H H H Br Br H

Reference synthesis

- 9 9 9

10 - - - 8 7 11

121.7ppm as a singlet. Assignments of C-4, C-5 and C-6 of 4 and 8 were made by comparison with the spectrum of 7.

The assignments of the remaining carbon resonances were based on chemical shift correlations, data reported for indole derivative^,^^ signal intensities in the partially relaxed spectra and multiplicities in the off-resonance proton decoupled spectra.

The substituent effects of the bromine on the aromatic carbons were fairly constant for 9 and 10 and, in the case of the benzene ring carbons, comparable to those reported for monosubstituted benzenes6

EXPERIMENTAL

I3C NMR spectra were obtained at 25.2MHz on a Varian XL-100-15 NMR spectrometer operating in the IT mode using a 62OL-100 computer interfaced to a Sykes 7000 dual disk drive. Samples were spun in 5mm tubes at cu27"C. Spectra were measured as 0.2-0.4 M solutions in chloroform-d or chloroform-d- methanol-d, mixtures, with TMS as internal standard, over a spectral width of 5400Hz using 35" pulses and a pulse repetition rate of 0.75 s. An 8K data table was used providing, after Fourier transformation, spectra with a digital resolution of 1.41 Hz per point.

Totally proton decoupled spectra are the results of 10 000 pulses, and were obtained by irradiation of the 'H spectrum at the central frequency of 5 ppm, with the irradiation frequency modulated by an external swept square-wave modulator.

Single-frequency off-resonance 'H decoupled spectra are the result of 25000 pulses, and were obtained by irradiating the 'H spectrum with a CW frequency at cu 0 ppm. Selectively decoupled spectra were obtained as above, but irradiating the desired 'H resonance with a low-power CW frequency. Lines were artificially broadened by cu 1 Hz by exponential weighting of the FID.

Indote (l), gramine (9, indole-3-carboxaldehyde (7) and indole-3-carboxylic acid (8) were purchased from Fluka. Ail other compounds were prepared by the procedures described in the literature (see references in Table 1); 6-d-indole (1, R, = 'H) and 6-d-gramine (5, R3 = 'H) were prepared as previously described by US.^ 6-d-Indole-3-carboxaldehyde (7, R3 = 'H) was obtained by formylation of 6-d-indole with phosphorus oxychloride in DMF.'

'

Acknowledgements

We thank the Consejo Nacional de Investigaciones Cientificas y T6cnicas de la Repfiblica Argentina and the Organization of the American States for partial financial support.

Table 2. uC chemical shifts of the indoles studied (ppm relative to internal TMS in chloroform-d solutions)

Compound C-2 c-3 C-4 C-5 C-6 C-7 C-6 c-9 Other carbons

1 123.9 102.5 120.6 119.5 121.7 110.7 127.5 135.5 - 2 122.0 116.4 118.2 119.1 121.8 111.5 126.2 136.5 36.9(CHZ) 3 123.2 113.8 118.6 119.4 121.9 111.5 127.1 136.5 46.7(CH2)

36.0 (CH,) 4 129.0 115.0 120.9 121.2 123.1 111.8 125.5 137.2 157.7(CH)

48.2 (CH,) 5 124.1 111.9 118.7 119.1 121.5 111.1 127.7 135.9 54.1 (CH,)

44.9 (CH,) 6 123.2 115.5 118.8 119.5 122.0 111.3 126.4 137.0 56.9(CH2) 7' 138.5 119.3 121.7 123.1 124.4 112.5 124.9 138.0 186.5(CHO) 8" 133.2 120.2 121.9 122.2 123.4 112.7 127.4 138.0 169.0(C02H) 9 124.6 102.6 121.7 122.8 115.2 113.7 126.5 136.3 -

10 125.0 111.3 119.9 122.5 115.2 114.1 126.5 136.8 53.7(CH2) 44.6 (CH,)

11 129.5 104.6 120.8 119.8 121.3 112.7 131.6 140.1 -0.2(CHJ

a Spectrum in chloroform-d-methanol-d, (2 : 1) solution.

2. G. W. Gribble, R. B. Nelson, J. L. Johnson and G. C. Levy,

3. E. Rosenberg, K. L. Williamson and J. D. Roberts, Org. J. Org. Chem. 40, 3720 (1975).

Magn. Reson. 8, 117 (1976).

References 1. A. A. Ghini, G. Burton and E. G. Gros, Phytochemistry21,

605 (1982).

831

Reference Data

4. M. Shamma and D. M. Hindenlang, Carbon-13 NMR Shift 8. G. Dellar, P. Djura and M. V. Sargent, J. Chem. SOC., Perkin Assignments of Amines and Alkaloids. Plenum Press, New York (1979). 9. J. Schallenberg and E. Meyer, 2. Naturforsch., Teil B, 38,

5. R. G. Parker and J. D. Roberts, J. Org. Chem. 35, 996 (1 970). 10. J. Thesing, Chem. Ber. 87,692 (1954).

6. J. B. Stothers, Carbon 13 NMR Spectroscopy, p. 197. 11. R. J. Sundberg and H. F. Russell, J. Org. Chem. 38, 3326 Academic Press, New York (1972).

7. A. A. Ghini, G. Burton and E. G. Gros, J. Labelled Compd. Radiopharm. in press.

Trans. 11679 (1981).

108 (1983).

(1973).

Received 10 March 1986; accepted 14April 1986

Proton NMR Data of Some 1J-Benzodithioles K. L. PARK and D. S. STEPHENSON

Institute of Organic Chemistry, University of Munich, Karlstrasse 23, 80oO Munich 2, FRG A. M. GRYFF-KELLER (to whom correspondence should be addressed) and P. SZCZECINSKI

Department of Chemistry, Technical University of Warsaw, Noakowskiego 3, 00-664 Warsaw, Poland

The 'H NMR spectra of 1,3-benzodithiole and eight derivatives have been analysed. Signals of the protons in positions 4 and 7 are shifted downfield compared with those for the protons in positions 5 and 6. The inter-ring proton-proton couplings have been determined.

INTRODUCTION

The considerable interest in 1,3-dithiole derivatives is connected with their utility in the preparation of 'organic metal,' i.e. organic materials of high electrical conductivity.la2 The abundant literature is also devoted to the interesting chemistry of 1,3-dithioles, which can react through nucleophilic carbene intermediate^.^'^ Since, to the best of our knowledge, the systematic elucidation of the proton NMR spectra of 1,3-benzodithioles has not been published, we report here the data for nine compounds belonging to this series. Their structures are given below.

7

l R = H , Y=CH, 1,3-Benzodithiole 2 R = H, Y = CHOCH, 2-Methoxy-l,3-benzodithiole

3 R = H , Y=C==C 'sm Dibenzotetrathiafulvalene 4 R = H , Y=C==S 2-Thioxo-l,3-benzodithiole 5 R = H, Y = CH+C104- 1,3-Benzodithiolium perchlorate 6 R=CH,,Y=CH, 5-Methyl-l,3-benzodithiole 7 R = CH,, Y = CHOCH, 8 R=CH,,Y=C==S 5-Methyl-Zthioxo-l,3-benzodithiole 9 R = CH,, Y = CSCH,+ClO,-

'S

2-Methoxy-5-methyl-l,3-benzodithiole

5-Methyl-2-methylthio-1,3-ben- zodithiolium perchlorate

DISCUSSION

The aromatic protons in 1-5 form a symmetrical AA'BB' spin system which, for 1, 2 and 5, is slightly perturbed by minute long-range coupling with proton 2. A automatic analysis of the spectra of such spin systems may lead to two statistically equivalent solutions differing only by permutation of the A and B chemical shifts. The choice of the correct solution was possible in our case on the basis of the results obtained for 6-9. These compounds have ABCX,, ABCMX, or ABCM2X, spin systems; thus, the automatic analysis of their spectra is unambiguous, the spectral assignment being made on the basis of the magnitudes of the coupling constants. The data in Tables 1 and 2 show that the chemical shift of an aromatic proton in any particular position increases in the order 1 < 2 i= 3 < 4 < 5 and 6 < 7 < 8 < 9. As deduced from the values of appropriate coupling constants, the alternation of the bonds in the benzene ring seems to become more pronounced in the same order. Moreover, for all investigated compounds the signals of protons 4 and 7 are shifted downfield compared with those of protons 5 and 6. These observations can be rationalized by considering the expected charge distribution and, in some cases, the aromatic-like character of the heterocyclic ring. The long-range coupling constants between proton 2 and the aromatic protons have been determined in 2 and 5. This type of coupling was recently observed for methylthiobenzene derivatives: but has not yet been reported for 1,3-benzodithiole systems.

~~~~~ ~~

Table 1. Proton chemical s h i s (ppm), coupling constants (Hz) and line widths (Hz) of 1,3-benzodithiole derivatives 1-5 Chemical shifts Coupling constants

Compound H-2 H-4,H-7 H-5, H-6 J(H-2, H-4) J(H-2, H-5) J(H-4, H-5) J(H-4, H-6) J(H-4, H-7) J(H-5, H-6) Line width

1 4.520 7.254 7.033 - - 7.78 1.22 0.47 7.34 0.20 2a 6.767 7.420 7.148 0.19 0.07 7.90 1.19 0.55 7.40 0.13 3 .__ 7.391 7.209 - _. 7.97 1.19 0.53 7.43 0.14 4 - 7.646 7.476 - - 8.16 1.17 0.60 7.46 0.15 5 11.431 8.761 8.085 0.18 0.29 8.51 1.08 0.69 7.23 0.12

a 6,,,,, = 3.132 ppm.