MAGNETIC RESONANCE IN CHEMISTRY Magn. Reson. Chem. 2005; 43: 346–347 Published online 27 January 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/mrc.1547
Spectral Assignments and Reference Data Detailed assignments of 1 H and 13 C NMR spectral data of 13 b-substituted cycloenones
RESULTS AND DISCUSSION Compounds 1–13 (Fig. 1) were prepared in our laboratory for synthetic studies purposes.6 ˇ-Acetoxycycloenones were prepared by reaction between cyclic ˇ-diketones and acetic anhydride in pyridine and DMAP. ˇ-Chlorocycloenones and ˇ-ethoxycycloenones were prepared by treating cyclic ˇ-diketones and the corresponding acetylated derivatives with NbCl5 (Scheme 1). Most of the 1 H and 13 C NMR signals could be assigned through straightforward analysis of 1D spectra combined with regular 2D COSY and HMQC. The only significant ambiguity is the assignment of methylene carbons on hydrogens corresponding to positions 4 and 6 (in compounds 1–11) or positions 4 and 5 (compounds 12 and 13). For compounds 1–11 the ambiguity could be removed through HMBC experiments, where only H-4 showed connectivity with C-3. For compounds 12 and 13, on the other hand, the HMBC data were inconclusive; double irradiation on signals of the complex system AA0 MM0 X3 , however, showed that only one pair of methylene hydrogens had a significant coupling constant with the methyl hydrogens; this methylene should then be the allylic methylene at
Mauricio Gomes Constantino,∗ Valdemar Lacerda Junior ´ and Gil Valdo Jose´ da Silva ˆ Departamento de Qu´ımica, Faculdade de Filosofia, Ciencias e Letras ˜ Preto, Universidade de Sao ˜ Paulo, Av. Bandeirantes 3900, de Ribeirao ˜ Preto, SP, Brazil 14040-901 Ribeirao Received 2 June 2004; revised 30 August 2004; accepted 10 September 2004
Detailed assignments of 1 H and 13 C NMR spectral data for 13 b-substituted cycloenones are reported. The assignments are based on 1D 1 H and 13 C NMR and on 2D shift-correlated (1 H,13 C-HMQC and HMBC), Jresolved and COSY and double irradiation experiments. Copyright 2005 John Wiley & Sons, Ltd. KEYWORDS: NMR; 1 H NMR; 13 C NMR; 1D NMR; 2D NMR; ˇ-substituted cycloenones
INTRODUCTION ˇ-Substituted cycloenones are important intermediates in organic synthesis and are frequently used in spiroannelation, alkylation and reduction reactions.1,2 As part of our investigations on the use of niobium pentachloride in organic synthesis,3 – 5 we recently prepared a number of ˇ-substituted cycloenones (ˇ-acetoxy-, ˇ-chloro- and ˇ-ethoxycycloenones) (Fig. 1);6 these compounds are derivatives of the enolic form of cyclic ˇ-diketones. During these studies we determined the structure of the products through careful analysis of 1 H and 13 C NMR spectra, with full assignment of chemical shifts and 1 H– 1 H coupling constants (J). In this paper we describe the results of this analysis.
Figure 1. Structures of compounds 1–13.
Ł Correspondence to: Mauricio Gomes Constantino, Departamento de Qu´ımica, Faculdade de Filosofia, Ciˆencias e Letras de Ribeir˜ao Preto, Universidade de S˜ao Paulo, Av. Bandeirantes 3900, 14040-901 Ribeir˜ao Preto, SP, Brazil. E-mail:
[email protected] Contract/grant sponsor: Funda¸ca˜ o de Amparo a` Pesquisa do Estado de S˜ao Paulo (FAPESP). Contract/grant sponsor: Conselho Nacional de Desenvolvimento Cient´ıfico e Tecnologico ´ (CNPq). Contract/grant sponsor: Coordenadoria de Aperfei¸coamento de Pessoal do Ensino Superior (CAPES).
Scheme 1. Preparation of ˇ-acetoxycycloenones, ˇ-chlorocycloenones and ˇ-ethoxycycloenones.
Table 1. 1 H NMR chemical shifts, υ (ppm), multiplicities and coupling constants, J(H,H) (Hz), for ˇ-substituted cycloenones 1–13a
Proton
1
2
3
2
5.89 t (1.1)
6.22 t (1.5)
4
2.54 td (6.2; 1.1) 2H 2.69 td (6.5; 1.5) 2H 2.41 t (6.4) 2H
5 6
2.06 quint (6.2) 2H 2.39 t (6.2) 2H
2.09 quint (6.5) 2H 2.40 t (6.5) 2H
1.98 quint (6.4) 2H — 2.33 t (6.4) 2H 2.27 s 2H
— 2.01 s 2H
— 2.20 s 2H
7 8 9
— 2.22 s —
— — —
3.91 q (7.0) 2H 1.37 t (7.0) —
— 2.21 s 1.10 s 6H
— — 1.10 s 6H
ax. 2.63 dd (16.0; 11.0) 3.90 q (7.0) — 1.36 t (7.0) 2.21 s 1.07 s 6H —
10 11 12 13
— — —
— — —
— — —
— — —
— — —
— — —
5.34 s
4 5.91 t (1.3)
5 6.22 t (1.5)
6 5.34 s
2.42 d (1.3) 2H 2.56 d (1.5) 2H 2.27 s 2H
7 6.01 d (2.1) eq. 2.87 ddd (17.0; 5.0; 2.1) ax. 2.66 dd (17.0; 11.0) 3.43 tt (11.0; 5.0) eq. 2.67 dd (16.0; 5.0)
7.26 m 2H 7.35 s 2H 7.26 m 1H —
Copyright 2005 John Wiley & Sons, Ltd.
347
Spectral Assignments and Reference Data Table 1. (Continued)
Proton
8
9
10
11
12
2 4
6.31 s 2.92 m 2H
5 6
2.02 quint (6.0) 2H 2.45 t (6.0) 2H
2.04 quint (6.0) 2H 2.45 t (6.0) 2H
2.52 m 2H —
2.55 m 2H —
7
3.45 dddd (12.0; 8.7; 7.2; 5.0) 3.35 ddt (12.6; 10.6; 5.3) eq. 2.71 dd (16.4; 5.0) eq. 2.61 ddd (16.5; 5.3; 1.3) ax. 2.62 dd (16.4; 12.0) ax. 2.55 dd (16.5; 12.6) 3.95 dq (10.0; 7.0)
8 9 10 11
— — — 7.25 m 2H
3.92 dq (10.0; 7.0) 1.36 t (7.0) — 7.25 m 2H
— 2.24 s — —
— — — —
— 2.30 s — —
— — — —
12 13 14
7.35 m 2H 7.25 m 1H —
7.34 m 2H 7.25 m 1H —
— — 1.66 t (2.0)
— — 1.91 t (2.0)
— — — — 1.63 t (2.0) 3H 1.78 t (2.0) 3H
a
5.43 d (1.3) — — — ax. 2.67 ddd (16.5; 10.6; 1.3) 2.54 tq (6.0; 2.0) 2H 2.74 tq (6.0; 2.0) 2H 2.84 m 2H eq. 2.65 ddd (16.5; 5.3; 1.3)
13 — 2.81 m 2H
In CDCl3 solution. All these assignments are in agreement with the J-resolved, HMQC and HMBC spectra.
Table 2.
Carbon
13
C NMR chemical shifts, υ (ppm), for ˇ-substituted cycloenones 1–13a
1
2
3
4
5
6
7
8
9
10
11
12
13
C-1 C-2 C-3
199.2 116.8 169.5
196.8 128.4 158.6
199.7 102.7 177.9
199.6 116.5 168.1
197.6 127.3 156.8
199.6 101.5 176.2
199.2 117.7 169.3
196.1 128.3 157.5
199.3 102.9 177.4
199.4 124.8 164.3
195.6 132.5 152.4
206.2 126.2 175.9
204.8 138.0 164.0
C-4 C-5 C-6 C-7
27.8 20.7 36.2 166.9
33.9 22.2 36.3 —
29.1 21.3 36.8 65.2
42.2 33.2 50.8 167.5
47.8 34.0 50.4 —
43.0 32.5 50.8 64.2
36.5 40.0 44.2 167.8
41.6 40.4 43.3 —
37.1 39.7 44.2 64.9
28.6 20.9 37.0 167.4
33.8 20.9 36.0 —
27.1 34.3 — 166.6
32.8 35.0 — —
CH3 -8 C-9 C-10 C-11
20.7 — — —
— — — —
14.1 — — —
21.3 28.1 — —
— 28.1 — —
14.1 28.3 — —
21.7 142.5 127.1 129.3
— 141.6 126.6 128.9
14.5 143.1 127.1 129.2
20.8 — — —
— — — —
21.1 — — —
— — — —
C-12 CH3 -13
— —
— —
— —
— —
— —
— —
127.7 —
127.4 —
127.1 —
— 8.3
— 11.3
— 6.6
— 8.3
a
In CDCl3 solution. All these assignments are in agreement with the HMQC and HMQC spectra.
position 4. Full assignments of the 1 H and summarized in Tables 1 and 2.
13 C
NMR signals are
EXPERIMENTAL NMR measurements 1H
NMR, 13 C NMR (13 Cf1 Hg and DEPT), COSY, J-resolved, HMQC and HMBC experiments were performed on a Bruker Avance DRX 500 spectrometer equipped with a 2.5 mm gradient probe. 1 H and 13 C spectra (at 500 and 125 MHz, respectively) were measured at 300 K at a concentration of 10 mg ml1 in CDCl3 as solvent. Tetramethylsilane was used as an internal reference. Chemical shifts are given on the υ scale. Typical conditions were as follows. For 1 H NMR analysis, 16 transients were acquired with a 1 s relaxation delay using 32K data points. The 90° pulse was 8.0 µs with a spectral width of 3612 Hz. 13 Cf1 Hg and DEPT spectra were obtained for a spectral width of 23 809 Hz, collecting 64K data points. The 90° pulse was 14.5 µs; 1024 transients were acquired for 13 Cf1 Hg and 512 transients for DEPT with a relaxation delay of 2 s. The HMBC, HMQC, COSY and J-resolved experiments were performed through standard pulse sequences, as suggested by the equipment manufacturer. The data for the HMQC, HMBC, COSY and J-resolved spectra were acquired with 1024 data points for t2 Copyright 2005 John Wiley & Sons, Ltd.
and 256 for t1 increments. The number of scans was 32, 64, 16 and 8, respectively.
Acknowledgments The authors thank the Funda¸ca˜ o de Amparo a` Pesquisa do Estado de S˜ao Paulo (FAPESP), the Conselho Nacional de Desenvolvimento Cient´ıfico e Tecnologico (CNPq) and the Coordenadoria de ´ Aperfei¸coamento de Pessoal do Ensino Superior (CAPES) for financial support. They also thank CBMM for NbCl5 samples.
REFERENCES 1. 2. 3. 4.
Wender PA, White AW. J. Am. Chem. Soc. 1988; 110: 2218. Clark RD, Heathcock CH. J. Org. Chem. 1976; 41: 636. Constantino MG, Lacerda V Jr, Arag˜ao V. Molecules 2001; 6: 770. Constantino MG, Lacerda V Jr, da Silva GVJ. Molecules 2002; 7: 456. 5. Constantino MG, Lacerda V Jr, da Silva GVJ. J. Heterocycl. Chem. 2003; 40: 369. 6. Constantino MG, Lacerda V Jr, da Silva Filho LC, da Silva GVJ. Lett. Org. Chem. 2004; 1: 360.
Magn. Reson. Chem. 2005; 43: 346–347