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The dipolar cyclo­addition of methyl acrylate to 1,5,6-tri­methyl-3-oxidopyrazinium

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aThe School of Chemistry, The University of Manchester, Manchester M13 9PL, England
*Correspondence e-mail: john.joule@manchester.ac.uk

(Received 14 February 2006; accepted 1 March 2006; online 8 March 2006)

5,6-Dimethyl­pyrazin-2-one reacts with iodo­methane to give a quaternary salt, deprotonation of which liberates a 3-oxidopyrazinium which undergoes a 1,3-dipolar cyclo­addition with methyl acrylate to form methyl 5,8-dimethyl-4-methyl­ene-2-oxo-3,8-diaza­bicyclo­[3.2.1]octane-6-exo-carboxyl­ate, C11H16N2O3, as the major product.

Comment

We have been investigating the 1,3-dipolar cyclo­addition chemistry of 3-oxidopyraziniums (Kiss et al., 1987[Kiss, M., Russell-Maynard, J. & Joule, J. A. (1987). Tetrahedron Lett. 28, 2187-2190.]; Allway et al., 1990[Allway, P. A., Sutherland, J. K. & Joule, J. A. (1990). Tetrahedron Lett. 31, 4781-4783.]; Yates et al., 1995[Yates, N. D., Peters, D. A., Allway, P. A., Beddoes, R. L., Scopes, D. I. C. & Joule, J. A. (1995). Heterocycles, 40, 331-347.]). These reactions efficiently produce bridged bicyclic systems, viz. 3,8-diaza­bicyclo­[3.2.1]octa­nes, which comprise key structural components of such biologically active natural products as anticancer quinocarcin (Takahashi & Tomita 1983[Takahashi, K. & Tomita, F. (1983). J. Antibiot. 36, 468-470.]; Tomita et al., 1983[Tomita, F., Takahashi, K. & Shimizu, K (1983). J. Antibiot. 36, 463-467.]; Hirayama & Shirahata, 1983[Hirayama, N. & Shirahata, K. (1983). J. Chem. Soc. Perkin Trans. 2, pp. 1705-1708.]) and anti­biotic lemonomycin (He et al., 2000[He, H., Shen, B. & Carter, G. T. (2000). Tetrahedron Lett. 41, 2067-2071.]). Our studies were initially inspired by the series of benchmark papers by Katritzky and co-workers [for reviews, see Dennis et al. (1976[Dennis, N., Katritzky, A. R. & Takeuchi, Y. (1976). Angew. Chem. Int. Ed. Engl. 15, 1-9.]) and Katritzky & Dennis (1989[Katritzky, A. & Dennis, N. (1989). Chem. Rev. 89, 827-861.])] on the cyclo­additions of 3-oxidopyridiniums. In neither Katritzky's extensive studies nor our own on 3-oxidopyraziniums had the possible influence of a substituent on the 1,3-dipole at one (or both) of the future ring-junction positions been assessed. This report describes our first study to remedy this omission, in which the reactivity of 1,5,6-trimethyl-3-oxidopyrazinium, (3) (see scheme; synthesis of 1,5,6-trimethyl-3-oxidopyrazinium and its reaction with methyl acrylate), was assessed.

[Scheme 1]

5,6-Dimethyl­pyrazin-2-one, (1) (Jones, 1949[Jones, R. G. (1949). J. Am. Chem. Soc. 71, 78-81.]; Karmas & Spoerri, 1952[Karmas, G. & Spoerri, P. E. (1952). J. Am. Chem. Soc. 74, 1580-1584.]), was reacted with iodo­methane to produce the methio­dide (2), treatment of which with triethyl­amine allowed the generation of the zwitterion (3), in situ and in the presence of methyl acrylate. The reactivity and regioselectivity of such 3-oxidodiaziniums is easily understood in terms of a resonance contributor [(3a) in this case]. The immediate products of the cyclo­additions [(4) in this case] are not isolated, but tautomerize to the enamide structure [(5) in this case], (5a) showing better the bicyclic nature of the product. A mixture of two isomeric products was formed from which the major isomer was isolated, crystalline, allowing an X-ray analysis to show that it was the exo-ester (4) (Fig. 1[link]). Thus, the additional oxidopyrazinium-6-methyl, appearing at the ring junction (C-5) in the cycloadduct, did not affect the efficiency or stereoselectivity of the cyclo­addition, compared with the comparable reaction of 1,5-dimethyl-3-oxidopyrazinium which also gave a 6-exo-ester as the major product (Yates et al., 1995[Yates, N. D., Peters, D. A., Allway, P. A., Beddoes, R. L., Scopes, D. I. C. & Joule, J. A. (1995). Heterocycles, 40, 331-347.]).

[Figure 1]
Figure 1
Plot of (4), with displacement ellipsoids drawn at the 50% probability level.

Experimental

5,6-Dimethyl­pyrazin-2-one (Jones, 1949[Jones, R. G. (1949). J. Am. Chem. Soc. 71, 78-81.]; Karmas & Spoerri, 1952[Karmas, G. & Spoerri, P. E. (1952). J. Am. Chem. Soc. 74, 1580-1584.]) (800 mg, 6.5 mmol) and iodo­methane (2 ml, 32.5 mmol, 5 equivalents) were heated under reflux in MeCN (150 ml) under nitro­gen for 24 h. The solvent was evaporated under vacuum and the residue extracted with CH2Cl2. Insoluble material was removed by filtration and the solution evaporated, leaving 3,4-dihydro-1,5,6-trimethyl-3-oxopyrazinium iodide as a dark-brown crystalline solid (1.12 g, 66%; m.p. >523 K); 1H NMR (D2O, 300 MHz, δ, p.p.m.)): 8.20 (1H, s, C2—H), 4.15 (3H, s, NMe), 2.50 and 2.45 (2 × s, 2 × 3H, 2 × CMe). Analysis found: C 32.31, H 4.02, N 10.39%; C7H11N2O requires: C 31.60, H 4.17, N 10.53%

A solution of 3,4-dihydro-1,5,6-trimethyl-3-oxopyrazinium iodide (1.5 g, 5.6 mmol), Et3N (1.6 ml, 11.2 mmol, 2 equivalents), and methyl acrylate (1.52 ml, 16.8 mmol, 3 equivalents) in dry MeCN (100 ml) was heated under reflux for 2 h. Solvents were removed from the resulting orange solution under vacuum, H2O (30 ml) was added and the product extracted into CH2Cl2 (3 × 30 ml). The combined dried extract was evaporated leaving a brown oil (0.88 g, 70%) from which, by careful chromatography over silica, eluting with n-hexa­ne–EtOAc (1:1), the major (thin-layer chromatography) adduct was obtained as colourless plates (330 mg, 26%; m.p. 383–388 K).

Crystal data
  • C11H16N2O3

  • Mr = 224.26

  • Monoclinic, P 21 /c

  • a = 9.818 (10) Å

  • b = 7.89 (2) Å

  • c = 14.80 (3) Å

  • β = 102.23 (8)°

  • V = 1120 (4) Å3

  • Z = 4

  • Dx = 1.330 Mg m−3

  • Mo Kα radiation

  • Cell parameters from 17414 reflections

  • θ = 2.1–25.0°

  • μ = 0.10 mm−1

  • T = 293 (2) K

  • Plate, colourless

  • 0.3 × 0.2 × 0.1 mm

Data collection
  • Rigaku R-AXIS II diffractometer

  • φ scans

  • Absorption correction: none

  • 17414 measured reflections

  • 1767 independent reflections

  • 1516 reflections with I > 2σ(I)

  • Rint = 0.037

  • θmax = 25.0°

  • h = 0 → 11

  • k = 0 → 9

  • l = −17 → 16

Refinement
  • Refinement on F2

  • R[F2 > 2σ(F2)] = 0.031

  • wR(F2) = 0.089

  • S = 1.03

  • 1767 reflections

  • 210 parameters

  • All H-atom parameters refined

  • w = 1/[σ2(Fo2) + (0.0555P)2 + 0.1608P] where P = (Fo2 + 2Fc2)/3

  • (Δ/σ)max = 0.003

  • Δρmax = 0.16 e Å−3

  • Δρmin = −0.13 e Å−3

  • Extinction correction: SHELXL97 (Sheldrick, 1997[Sheldrick, G. M. (1997). SHELXL97. University of Göttingen, Germany.])

  • Extinction coefficient: 0.037 (6)

Table 1
Hydrogen-bond geometry (Å, °)[link]

D—H⋯A D—H H⋯A DA D—H⋯A
N1—H1⋯O1i 0.913 (18) 2.082 (19) 2.980 (6) 167.6 (15)
Symmetry code: (i) [-x+1, y-{\script{1\over 2}}, -z+{\script{3\over 2}}].

H atoms were found by difference Fourier methods and refined isotropically, with refined C—H distances in the range 0.932 (15)–1.041 (19) Å and an N—H distance of 0.913 (18) Å.

Data collection: MSC Diffractometer Control Software (Molecular Structure Corporation, 1992[Molecular Structure Corporation (1992). MSC Diffractometer Control Software. MSC, 3200 Research Forest Drive, The Woodlands, TX 77381, USA.]); cell refinement: DENZO (Otwinowski & Minor, 1987[Otwinowski, Z. & Minor, W. (1987). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307-326. New York: Academic Press.]); data reduction: DENZO; program(s) used to solve structure: SAPI91 (Fan, 1991[Fan, H.-F. (1991). SAPI91. Rigaku Corporation, Tokyo, Japan.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997[Sheldrick, G. M. (1997). SHELXL97. University of Göttingen, Germany.]); molecular graphics: SHELXTL (Bruker, 2001[Bruker (2001). SHELXTL. Version 6.12. Bruker AXS Inc., Madison, Wisconsin, USA.]); software used to prepare material for publication: TEXSAN (Molecular Structure Corporation, 1995[Molecular Structure Corporation (1995). TEXSAN. Version 1.7. MSC, 3200 Research Forest Drive, The Woodlands, TX 77381, USA.]).

Supporting information


Computing details top

Data collection: MSC R-AXIS 11 Control (Molecular Structure Corporation, 1992); cell refinement: DENZO (Otwinowski, 1988); data reduction: DENZO (Otwinowski, 1988); program(s) used to solve structure: SAPI91 (Fan, 1991); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 2001); software used to prepare material for publication: TEXSAN (Molecular Structure Corporation, 1995).

methyl 8-methyl-4-methylene-2-oxo-3,8-diazabicyclo[3.2.1]octane-6-exo-carboxylate top
Crystal data top
C11H16N2O3F(000) = 480
Mr = 224.26Dx = 1.330 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71069 Å
a = 9.818 (10) ÅCell parameters from 17414 reflections
b = 7.89 (2) Åθ = 2.1–25.0°
c = 14.80 (3) ŵ = 0.10 mm1
β = 102.23 (8)°T = 293 K
V = 1120 (4) Å3Plate, colourless
Z = 40.3 × 0.2 × 0.1 mm
Data collection top
Rigaku R-AXIS
diffractometer
1516 reflections with I > 2σ(I)
Radiation source: Rigaku rotating anodeRint = 0.037
Graphite monochromatorθmax = 25.0°, θmin = 2.1°
116 × 3° φ scansh = 011
17414 measured reflectionsk = 09
1767 independent reflectionsl = 1716
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.031All H-atom parameters refined
wR(F2) = 0.089 w = 1/[σ2(Fo2) + (0.0555P)2 + 0.1608P]
where P = (Fo2 + 2Fc2)/3
S = 1.03(Δ/σ)max = 0.003
1767 reflectionsΔρmax = 0.16 e Å3
210 parametersΔρmin = 0.13 e Å3
0 restraintsExtinction correction: SHELXL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.037 (6)
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
O10.49890 (11)0.24550 (13)0.76055 (8)0.0498 (3)
O21.10556 (10)0.28198 (14)0.63198 (8)0.0523 (3)
O30.99596 (11)0.53179 (13)0.62400 (8)0.0519 (3)
N10.62845 (13)0.06832 (15)0.69294 (8)0.0394 (3)
H10.5847 (18)0.021 (2)0.7137 (12)0.058 (5)*
N20.67389 (11)0.32417 (14)0.57739 (7)0.0347 (3)
C10.58496 (14)0.22418 (17)0.71177 (9)0.0360 (4)
C20.65104 (15)0.36832 (17)0.66899 (9)0.0367 (4)
H20.5926 (16)0.469 (2)0.6655 (10)0.043 (4)*
C30.79972 (16)0.3988 (2)0.72487 (11)0.0446 (4)
H3A0.8088 (16)0.369 (2)0.7904 (13)0.053 (4)*
H3B0.8251 (18)0.517 (2)0.7213 (12)0.056 (5)*
C40.89119 (14)0.28417 (18)0.67810 (10)0.0370 (4)
H40.9360 (14)0.2009 (19)0.7184 (10)0.036 (4)*
C50.78439 (13)0.19369 (16)0.59858 (9)0.0336 (3)
C60.72950 (14)0.03561 (16)0.63962 (9)0.0348 (3)
C70.54837 (17)0.2728 (2)0.50992 (11)0.0467 (4)
H7A0.4741 (18)0.362 (2)0.5114 (11)0.058 (5)*
H7B0.5689 (18)0.261 (2)0.4480 (14)0.059 (5)*
H7C0.5091 (17)0.160 (2)0.5271 (12)0.062 (5)*
C81.00029 (14)0.38310 (19)0.64213 (9)0.0386 (4)
C91.21255 (18)0.3595 (3)0.59168 (15)0.0615 (5)
H9A1.1729 (19)0.391 (2)0.5257 (15)0.074 (6)*
H9B1.250 (2)0.452 (3)0.6286 (16)0.079 (6)*
H9C1.289 (3)0.273 (3)0.5965 (16)0.094 (7)*
C100.83963 (18)0.1504 (2)0.51235 (11)0.0470 (4)
H10A0.8685 (17)0.257 (2)0.4818 (12)0.054 (4)*
H10B0.9270 (19)0.078 (2)0.5311 (12)0.065 (5)*
H10C0.7628 (18)0.087 (2)0.4651 (13)0.062 (5)*
C110.76950 (18)0.12241 (19)0.63052 (12)0.0500 (4)
H11A0.8372 (17)0.147 (2)0.5951 (12)0.053 (4)*
H11B0.7307 (19)0.215 (2)0.6613 (13)0.062 (5)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0585 (7)0.0439 (6)0.0569 (7)0.0033 (5)0.0350 (6)0.0006 (5)
O20.0375 (6)0.0560 (7)0.0653 (7)0.0066 (5)0.0154 (5)0.0031 (5)
O30.0581 (7)0.0384 (7)0.0619 (7)0.0046 (5)0.0189 (5)0.0011 (5)
N10.0489 (7)0.0294 (7)0.0450 (7)0.0020 (5)0.0215 (6)0.0055 (5)
N20.0397 (6)0.0314 (6)0.0348 (6)0.0048 (5)0.0121 (5)0.0027 (5)
C10.0410 (8)0.0336 (8)0.0358 (7)0.0041 (6)0.0138 (6)0.0006 (6)
C20.0453 (8)0.0285 (8)0.0404 (8)0.0070 (6)0.0182 (6)0.0006 (6)
C30.0544 (9)0.0413 (9)0.0417 (9)0.0064 (7)0.0184 (7)0.0105 (7)
C40.0402 (8)0.0342 (8)0.0361 (8)0.0023 (6)0.0070 (6)0.0032 (6)
C50.0379 (8)0.0292 (7)0.0359 (7)0.0036 (5)0.0127 (6)0.0010 (5)
C60.0379 (7)0.0308 (8)0.0362 (7)0.0032 (6)0.0090 (6)0.0012 (5)
C70.0453 (9)0.0505 (10)0.0425 (9)0.0030 (7)0.0052 (7)0.0063 (7)
C80.0373 (8)0.0407 (9)0.0365 (7)0.0001 (6)0.0049 (6)0.0027 (6)
C90.0384 (9)0.0866 (15)0.0620 (12)0.0051 (10)0.0164 (8)0.0053 (11)
C100.0529 (10)0.0485 (10)0.0452 (9)0.0005 (8)0.0231 (8)0.0074 (7)
C110.0575 (10)0.0318 (9)0.0642 (10)0.0053 (7)0.0212 (8)0.0024 (7)
Geometric parameters (Å, º) top
O1—C11.234 (2)C4—C51.572 (3)
O2—C81.339 (2)C4—H40.932 (15)
O2—C91.448 (3)C5—C101.527 (3)
O3—C81.202 (3)C5—C61.534 (3)
N1—C11.349 (3)C6—C111.322 (4)
N1—C61.416 (2)C7—H7A1.018 (18)
N1—H10.913 (18)C7—H7B0.983 (19)
N2—C21.462 (3)C7—H7C1.026 (19)
N2—C71.469 (3)C9—H9A1.00 (2)
N2—C51.480 (3)C9—H9B0.94 (2)
C1—C21.513 (3)C9—H9C1.01 (2)
C2—C31.537 (3)C10—H10A1.025 (18)
C2—H20.972 (16)C10—H10B1.018 (19)
C3—C41.538 (3)C10—H10C1.041 (19)
C3—H3A0.982 (18)C11—H11A0.950 (17)
C3—H3B0.973 (18)C11—H11B0.978 (19)
C4—C81.510 (3)
C8—O2—C9116.07 (19)N2—C5—C4100.71 (16)
C1—N1—C6124.80 (12)C10—C5—C4115.36 (15)
C1—N1—H1116.3 (11)C6—C5—C4107.89 (16)
C6—N1—H1118.8 (11)C11—C6—N1119.13 (14)
C2—N2—C7115.11 (15)C11—C6—C5126.09 (18)
C2—N2—C5102.63 (13)N1—C6—C5114.77 (15)
C7—N2—C5115.08 (16)N2—C7—H7A107.2 (9)
O1—C1—N1122.07 (13)N2—C7—H7B110.5 (10)
O1—C1—C2123.38 (16)H7A—C7—H7B111.9 (14)
N1—C1—C2114.55 (18)N2—C7—H7C112.1 (10)
N2—C2—C1111.89 (16)H7A—C7—H7C106.9 (14)
N2—C2—C3102.78 (14)H7B—C7—H7C108.2 (14)
C1—C2—C3109.57 (14)O3—C8—O2123.22 (16)
N2—C2—H2110.5 (9)O3—C8—C4126.06 (14)
C1—C2—H2109.4 (9)O2—C8—C4110.72 (19)
C3—C2—H2112.6 (9)O2—C9—H9A109.9 (11)
C2—C3—C4104.17 (15)O2—C9—H9B108.4 (13)
C2—C3—H3A111.8 (9)H9A—C9—H9B113.3 (18)
C4—C3—H3A111.4 (10)O2—C9—H9C106.3 (13)
C2—C3—H3B110.2 (10)H9A—C9—H9C111.5 (18)
C4—C3—H3B111.1 (10)H9B—C9—H9C107.1 (18)
H3A—C3—H3B108.2 (14)C5—C10—H10A111.4 (10)
C8—C4—C3112.36 (19)C5—C10—H10B109.0 (10)
C8—C4—C5112.40 (16)H10A—C10—H10B106.5 (14)
C3—C4—C5104.07 (15)C5—C10—H10C109.5 (10)
C8—C4—H4108.4 (8)H10A—C10—H10C109.1 (14)
C3—C4—H4111.5 (9)H10B—C10—H10C111.3 (14)
C5—C4—H4108.0 (9)C6—C11—H11A120.2 (10)
N2—C5—C10110.64 (14)C6—C11—H11B120.1 (11)
N2—C5—C6110.23 (16)H11A—C11—H11B119.7 (15)
C10—C5—C6111.47 (16)
C6—N1—C1—O1178.22 (13)C8—C4—C5—N292.40 (16)
C6—N1—C1—C21.3 (2)C3—C4—C5—N229.43 (13)
C7—N2—C2—C157.34 (16)C8—C4—C5—C1026.72 (18)
C5—N2—C2—C168.45 (18)C3—C4—C5—C10148.56 (14)
C7—N2—C2—C3174.81 (12)C8—C4—C5—C6152.07 (12)
C5—N2—C2—C349.02 (16)C3—C4—C5—C686.09 (18)
O1—C1—C2—N2144.21 (14)C1—N1—C6—C11176.04 (14)
N1—C1—C2—N236.25 (18)C1—N1—C6—C52.9 (2)
O1—C1—C2—C3102.47 (18)N2—C5—C6—C11149.07 (16)
N1—C1—C2—C377.07 (18)C10—C5—C6—C1125.8 (2)
N2—C2—C3—C428.60 (15)C4—C5—C6—C11101.83 (19)
C1—C2—C3—C490.5 (2)N2—C5—C6—N132.04 (17)
C2—C3—C4—C8120.99 (15)C10—C5—C6—N1155.31 (13)
C2—C3—C4—C50.87 (15)C4—C5—C6—N177.05 (17)
C2—N2—C5—C10171.11 (11)C9—O2—C8—O33.8 (2)
C7—N2—C5—C1063.08 (18)C9—O2—C8—C4175.82 (13)
C2—N2—C5—C665.14 (15)C3—C4—C8—O322.0 (2)
C7—N2—C5—C660.67 (19)C5—C4—C8—O394.99 (18)
C2—N2—C5—C448.63 (14)C3—C4—C8—O2158.37 (13)
C7—N2—C5—C4174.43 (11)C5—C4—C8—O284.64 (16)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O1i0.913 (18)2.082 (19)2.980 (6)167.6 (15)
Symmetry code: (i) x+1, y1/2, z+3/2.
 

Acknowledgements

YY gratefully acknowledges a studentship from the University of Manchester.

References

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