Chemistry of Polyhalogenated Nitrobutadienes, Part 5: Synthesis and ­Reactions of Dichloromethyl Nitrovinylidene Ketones of Heterocycles

Abstract

An easy access to dichloromethyl nitrovinylidene ketones of five-membered heterocycles is presented starting from nitroperchlorobutadiene. These complex ketones are valuable starting materials for novel product structures in versatile reactions such as selective reductions, substitutions to give α-nitroacryl cyanides, fragmentations by means of an alkoxide, as well as ring-cleavage/ring-closure steps by the action of hydrazine. Some of the products show biological activity in crop protection.

nitro compound - haloalkene - ketone - cyclization - heterocycle

References and Notes

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4

Crystal Data for 7 have been deposited with the Cambridge Crystallographic Data Center (CCDC 632420) and may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK [fax:[phone]; e-mail: [e-mail] or www.ccdc.cam.ac.uk].

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13

Experimental Details
¹H NMR and ¹³C NMR spectra were obtained on a BRUKER Avance 400. Proton spectra were referenced to TMS; ¹³C NMR spectra refer to the solvent signal at δ = 77.0 ppm. Spectra in DMSO-d ₆ were referenced to δ = 2.50 ppm (¹H) and 39.7 ppm (¹³C), respectively. High-resolution mass spectra were measured with a Bruker Daltonik APEX IV FT Ion Cyclotron Resonance mass spectrometer with electrospray ionization.
1-(2-Chloro-5-pyridylmethyl)-2-(2,3,3-trichloro-1-nitro-allylidene)imidazolidine ( 3)
To a solution of 7.19 g (38.7 mmol) N-(2-chloro-5-pyridyl-methyl)ethane-1,2-diamine in 30 mL MeOH was added a solution of 5.00 g (18.4 mmol) 1,1,2,4,4-pentachloro-3-nitro-1,3-butadiene (1) in 5 mL MeOH at -40 °C within 5 min. The resulting mixture was kept at -40 °C for 1 h, then 1 h at r.t. The precipitate was sucked off, washed with H₂O (3 × 20 mL), MeOH (1 × 10 mL), and Et₂O (2 × 20 mL). Drying in vacuo yielded 3.19 g (45%) of imidazolidine 3, mp 174-175 °C. ¹H NMR (DMSO-d ₆): δ = 3.78 (br s, 4 H, NCH₂CH₂), 4.56 (br s, 2 H, H₂CC_aryl), 7.54 (d, J = 8.3 Hz, 1 H, H-3_aryl), 7.77 (dd, J = 8.3, 2.4 Hz, 1 H, H-4_aryl), 8.35 (d, J = 2.4 Hz, 1 H, H-6_aryl), 9.41 (br s, 1 H, NH). ¹³C NMR (DMSO-d ₆): δ = 42.7, 49.5, 51.0 (3 CH₂), 103.3 (CNO₂), 124.4 (CH), 125.3, 125.6 (CCl=CCl₂), 131.5 (C_quat), 137.9 (CH), 147.9 (N=CH), 149.6 (NCCl), 159.8 (NCNH). HRMS (ESI) [M + H]⁺: m/z calcd for C₁₂H₁₀Cl₄N₄O₂: 382.9631; found: 382.9632.
2-(2,3,3-Trichloro-1-nitroallylidene)-1,3-dimethyl-imidazolidine ( 4) In analogy to the preparation of 3, the dissolved nitro-perchlorobutadiene (1) was added to a solution of N,N′-dimethylethane-1,2-diamine (85% in H₂O) in 20 mL MeOH. After completion of the reaction, 200 mL of cold H₂O was added. Then, the aqueous phase was extracted with CHCl₃ (3 × 20 mL). The organic layer was washed twice with H₂O and dried over anhyd CaCl₂. Removal of the solvent in vacuo afforded a crude product that was reprecipitated with Et₂O (20 mL). Drying in vacuo again yielded 3.43 g (65%) imidazolidine 4, mp 122-124 °C. ¹H NMR (CDCl₃): δ = 3.00 (s, 6 H, NMe), 3.86 (br s, 4 H, NCH₂). ¹³C NMR (CDCl₃): δ = 35.4 (CH₃), 49.8 (CH₂), 99.6 (CNO₂), 120.9, 125.4 (CCl=CCl₂), 162.0 (NCN). HRMS (ESI) [M + H]⁺: m/z calcd for C₈H₁₀Cl₃N₃O₂: 285.9914; found: 285.9913.
General Procedure for the Synthesis of 2-Nitrobuten-3-ones 7-11
A suspension of 5.00 mmol of the heterocycles 2-6 in 20 mL MeOH each was treated with 2.25 g (20.0 mmol) of a 40% solution of Me₂NH in H₂O. The mixture was then kept at 45-50 °C for the required reaction time, according to TLC (typically 2-10 h). After cooling to 5 °C, excessive amine was neutralized with concentrated HCl. Stirring at 30-70 °C (3-6 h, TLC monitoring), recooling to r.t., and adding of H₂O (100 mL) then yielded a precipitate which was washed twice with H₂O (2 × 20 mL) and Et₂O (2 × 20 mL), in detail:
1,1-Dichloro-3-(imidazolidin-2-ylidene)-3-nitropropan-2-one ( 7) Reaction times: 6 h with Me₂NH, 5 h with HCl at 40-45 °C; 80% yield; mp 169-170 °C. ¹H NMR (DMSO-d ₆): δ = 3.69 (br s, 4 H, NCH₂CH₂N), 7.35 (s, 1 H, Cl₂CH), 9.12 (br s, 2 H, NH). ¹³C NMR (DMSO-d ₆): δ = 43.6 (2 CH₂), 70.9 (CHCl₂), 113.6 (CNO₂), 159.6 (NHCNH), 180.4 (C=O). HRMS (ESI) [M + H]⁺: m/z calcd for C₆H₇Cl₂N₃O₃: 239.9937; found: 239.9937.
1,1-Dichloro-3-{1-[(2-chloro-5-pyridyl)methyl]imid-azolidin-2-ylidene}-3-nitropropan-2-one ( 8)
Reaction times: 10 h with Me₂NH, 5 h with HCl at 40-45 °C; 60% yield; mp 171-173 °C. ¹H NMR (DMSO-d ₆): δ = 3.87 (br s, 4 H, NCH₂CH₂N), 4.46 (br s, 2 H, NCH₂), 7.49 (s, 1 H, CHCl₂), 7.56 (d, 1 H, J = 8.3 Hz, H-3_aryl), 7.76 (dd, 1 H, J = 8.3, 2.4 Hz, H-4_aryl), 8.33 (d, 1 H, J = 2.4 Hz, H-6_aryl), 10.31 (br s, 1 H, NH). ¹³C NMR (DMSO-d ₆): δ = 42.8, 46.6, 47.9 (3 CH₂), 69.5 (CHCl₂), 107.5 (CNO₂), 124.6 (CCl=CH), 129.9 (CHCCH), 140.0 (CH), 150.0 (N=CH), 150.3 (NCCl), 162.5 (NCNH), 175.4 (C=O). HRMS (ESI) [M + H]⁺: m/z calcd for C₁₂H₁₁Cl₃N₄O₃: 364.9970; found: 364.9971.
1,1-Dichloro-3-(1,3-dimethylimidazolidin-2-ylidene)-3-nitropropan-2-one ( 9)
Reaction times: 6 h with Me₂NH, 6 h with HCl at 35-40 °C; 45% yield; mp 150-151 °C. ¹H NMR (DMSO-d ₆): δ = 2.86 (s, 6 H, NCH₃), 3.91 (br s, 4 H, NCH₂CH₂), 7.54 (s, 1 H, CHCl₂). ¹³C NMR (DMSO-d ₆): δ = 33.6 (CH₃), 49.1 (2 CH₂), 69.8 (CHCl₂), 106.4 (CNO₂), 161.9 (NCN), 175.3 (C=O). HRMS (ESI) [M + H]⁺: m/z calcd for C₈H₁₁Cl₂N₃O₃: 268.0250; found: 268.0252.
As a side product, trichloroacrylic acid (12) was isolated: After the aforementioned acidic hydrolysis the mixture was treated with an excess of 10% NaHCO₃ in H₂O at 10 °C and set to pH 9. The usual extraction as described above then gave 9, whereas the basic aqueous solution was acidified with HCl, extracted with CH₂Cl₂ (2 × 20 mL), washed with H₂O (2 × 10 mL) and dried over anhyd Na₂SO₄. Evaporation of the solvent yielded 12 (30%), mp 71-73 °C (lit. [14] 73-74 °C). ¹H NMR (CDCl₃): δ = 11.0 (br s, 1 H, COOH). ¹³C NMR (CDCl₃): δ = 121.7 (CCl), 134.6 (CCl₂), 165.8 (C=O).
1,1-Dichloro-3-nitro-3-(thiazolidin-2-ylidene)propan-2-one ( 10)
Reaction times: 2 h with Me₂NH, 3 h with HCl at 65-70 °C; 50% yield; mp 130-131 °C. ¹H NMR (DMSO-d ₆): δ = 3.31 (t, 2 H, J = 8.6 Hz, SCH₂), 4.07 (t, 2 H, J = 8.6 Hz, NCH₂), 7.36 (s, 1 H, CHCl₂), 10.83 (br s, 1 H, NH). ¹³C NMR (DMSO-d ₆): δ = 29.0 (SCH₂), 51.7 (NCH₂), 70.8 (CHCl₂), 120.7 (CNO₂), 173.9 (HNCS), 180.1 (C=O). HRMS (ESI) [M + H]⁺: m/z calcd for C₆H₆Cl₂N₂O₃S: 256.9549; found: 256.9550.
1,1-Dichloro-3-(1,3-dithiolan-2-ylidene)-3-nitropropan-2-one ( 11)
Reaction times: 3 h with Me₂NH, 3 h with HCl at 30-35 °C; 90% yield; mp 140-141 °C. ¹H NMR (CDCl₃): δ = 3.58 (m, 4 H, CH₂), 7.12 (s, 1 H, CHCl₂). ¹³C NMR (DMSO-d ₆): δ = 38.3, 39.1 (2 SCH₂), 69.0 (CHCl₂), 133.0 (CNO₂), 180.3 (SCS), 187.4 (C=O). HRMS (EI) [M + H]⁺: m/z calcd for C₆H₅Cl₂NO₃S₂: 273.9161; found: 273.9162.
1,1-Dichloro-3-nitro-3-(thiazolidin-2-ylidene)propan-2-ol ( 13)
To a solution of 0.30 g (1.17 mmol) nitrobutenone 10 in 20 mL EtOH at 0 °C was added 0.049 g (1.30 mmol) NaBH₄ within 2 min. The resulting mixture was kept at 0 °C for 10 min and for additional 15 min at 10 °C. After addition of 50 mL cold H₂O and neutralization with 5% HCl, the precipitate that was formed was sucked off and washed with H₂O (3 × 20 mL). Drying in vacuo yielded 0.24 g (80%) nitrobutenol 13; mp 122-124 °C. ¹H NMR (DMSO-d ₆): δ = 3.13 (t, 2 H, J = 8.6 Hz, SCH₂), 3.86 (t, 2 H, J = 8.6 Hz, NCH₂), 5.33 (br s, 1 H, CHCNO₂), 6.35 (d, 1 H, J = 5.2 Hz, CHCl₂), 7.15 (br s, 1 H, OH), 8.90 (br s, 1 H, NH). ¹³C NMR (DMSO-d ₆): δ = 28.4 (SCH₂), 50.3 (NCH₂), 74.1, 75.0 [CH(OH)CHCl₂], 116.8 (CNO₂), 169.5 (HNCS). HRMS (ESI) [M + H]⁺: m/z calcd for C₆H₈Cl₂N₂O₃S: 258.9705; found: 258.9707.
1,1-Dichloro-3-(1,3-dithiolan-2-ylidene)-3-nitropropan-2-ol ( 14)
Preparation as described for 13; 98% yield; mp 135-136 °C. ¹H NMR (CDCl₃): δ = 3.58 (m, 4 H, CH₂), 4.00 (d, 1 H, J = 10.5 Hz, OH), 5.11 (dd, 1 H, J = 10.5, 8.7 Hz, CHOH), 6.23 (d, 1 H, J = 8.7 Hz, CHCl₂). ¹³C NMR (CDCl₃): δ = 38.0, 39.4 (2 SCH₂), 72.5 (CHCl₂), 78.5 [CH(OH)], 132.2 (CNO₂), 173.4 (SCS). HRMS (ESI) [M + Na]⁺: m/z calcd for C₆H₇Cl₂NO₃S₂: 297.9137; found: 297.9139.
1,1-Dichloro-3-(1,3-dithiolan-2-yl)-3-nitropropan-2-ol ( 15) (1) Starting from nitropropanol 14 in analogy to the synthesis of 13, 152 mg, 50% yield.
(2) Directly from nitropropanone 11 under modified conditions: To a suspension of 0.30 g (1.09 mmol) nitrobutenone 11 in 20 mL EtOH at 0 °C was added 0.045 g (1.20 mmol) NaBH₄ within 2 min. The resulting mixture was kept at 0 °C for 10 min and at 10 °C for 15 min. In contrast to the reaction described above, in this case another portion (0.045 g, 1.20 mmol) of NaBH₄ was added, and the mixture was kept at 10 °C for additional 60 min. After addition of 50 mL cold H₂O, neutralization with 5% HCl, and extraction with CH₂Cl₂ (3 × 20 mL), the organic layer was washed with H₂O and dried over anhyd CaCl₂. Evaporation of the solvent and column chromatography (PE-EtOAc, 10:1) yielded a yellow oil, 106 mg (35%) of 15 as a mixture of erythro- und threo-isomers (5:1 ratio according to NMR). ¹H NMR (CDCl₃): δ (major isomer) = 3.29 (m, 5 H, SCH₂CH₂S, OH), 4.49 (m, 1 H, CHOH), 4.89 (dd, 1 H, J = 10.2, 8.1 Hz, CHNO₂), 5.18 (d, 1 H, J = 10.2 Hz, SCHS), 5.81 (d, 1 H, J = 8.1 Hz, CHCl₂); δ (minor isomer) = 3.29 (m, 5 H, SCH₂CH₂S, OH), 4.49 (m, 1 H, CHOH), 4.92 (dd, 1 H, J = 8.5, 6.0 Hz, CHNO₂), 5.25 (d, 1 H, J = 8.5 Hz, SCHS), 6.12 (d, 1 H, J = 6.0 Hz, CHCl₂). ¹³C NMR (CDCl₃): δ (major isomer) = 37.9, 38.7 (SCH₂CH₂S), 50.6 (SCHS), 72.5 (CHCl₂), 76.0 (CHOH), 90.5 (CHNO₂); δ (minor isomer) = 37.8, 38.7 (SCH₂CH₂S), 49.9 (SCHS), 73.0 (CHCl₂), 77.3 (CHOH), 91.7 (CHNO₂). HRMS (ESI) [M + Na]⁺: m/z calcd for C₆H₉Cl₂NO₃S₂: 299.9293; found: 299.9295.
1,1-Dichloro-3-(1,3-dithiolan-2-ylidene)-3-nitropropan-2-yl Acetate ( 16) A mixture of 0.30 g (1.09 mmol) nitrobutenol 14 and 0.18 g (2.18 mmol) NaOAc in 10 mL Ac₂O were stirred for 4 h under reflux. After cooling to r.t. the mixture was diluted with 60 mL cold H₂O. The resulting precipitate was sucked off and washed thoroughly with H₂O (5 × 20 mL). Drying in vacuo yielded 0.33 g (95%) acetate 16, mp 119-120 °C. ¹H NMR (CDCl₃): δ = 2.15 (s, 3 H, CH₃), 3.58 (m, 4 H, CH₂), 6.39 (d, 1 H, J = 8.8 Hz, CHO), 6.54 (d, 1 H, J = 8.8 Hz, CHCl₂). ¹³C NMR (CDCl₃): δ = 20.4 (CH₃), 38.1, 39.2 (2 SCH₂), 70.5 (CHCl₂), 76.2 (CHO), 130.4 (CNO₂), 169.2 (C=O), 173.3 (SCS). HRMS (ESI) [M + Na]⁺: m/z calcd for C₈H₉Cl₂NO₄S₂: 339.9242; found: 339.9242
2-(Nitromethylene)-1,3-dithiolane ( 17) To a solution of 0.30 g (1.09 mmol) nitrobutenone 11 in 20 mL EtOH at r.t. was added 0.15 g (2.20 mmol) NaOEt. The resulting mixture was kept at r.t. for 1 d. After cooling to 10 °C, addition of 60 mL cold H₂O and neutralization with concd HCl, the resulting precipitate was sucked off and washed with H₂O (2 × 20 mL). Drying in vacuo afforded 0.13 g (73%) dithiolane 17, mp 105-106 °C (lit. [6a] [c] 105-106 °C). ¹H NMR (CDCl₃): δ = 3.54 (br s, 4 H, SCH₂), 7.57 (s, 1 H, CH). ¹³C NMR (CDCl₃): δ = 36.8, 38.7 (2 SCH₂), 124.0 (CHNO₂), 167.4 (SCS).
3-Hydrazonomethyl-5-(2-mercaptoethyl)sulfanyl-4-nitro-1 H -pyrazol ( 18) A suspension of 0.30 g (1.09 mmol) 11 in 15 mL MeOH was treated with 0.27 g (5.45 mmol) N₂H₄·H₂O (64% in H₂O) at r.t. The resulting mixture was stirred for 5 h at the same temperature. Then the precipitate was sucked off, washed twice with H₂O and once with MeOH (10 mL each portion). After drying in vacuo 0.20 g (75%) pyrazole 18 was obtained; mp 216-218 °C. ¹H NMR (DMSO-d ₆): δ = 2.64 (br s, 1 H, SH), 2.82 (m, 2 H, HSCH ₂ ), 3.27 (m, 2 H, CSCH ₂ ), 8.03 (s, 1 H, N=CH), 8.20 (br s, 2 H, NH₂), 13.83 (br s, 1 H, NH). ¹³C NMR (DMSO-d ₆): δ = 23.7 (HSCH₂), 33.5 (CSCH₂), 122.1 (N=CH), 127.0 (CNO₂), 140.9 (N=C), 145.3 (NHCS). HRMS (ESI) [M + H]⁺: m/z calcd for C₆H₉N₅O₂S₂: 248.0270; found: 248.0271.
Acetic Acid [5-(2-Mercapto-ethylsulfanyl)-4-nitro-1 H -pyrazol-3-ylmethylene]hydrazide ( 19)
A solution of 0.20 g (0.81 mmol) pyrazole 18 in 15 mL Ac₂O was kept at 20 °C for 3 h. The precipitate was sucked off, washed with H₂O (2 × 10 mL) and MeOH (1 × 10 mL) and dried in vacuo yielding 0.22 g (95%) pyrazole 19 (Z:E = 1:0.4); mp 213-215 °C. ¹H NMR (DMSO-d ₆): δ (major isomer) = 2.24 s (3 H, CH₃), 2.66 br s (1 H, SH), 2.85 m (2 H, HSCH ₂ ), 3.30 m (2 H, CSCH ₂ ), 8.36 s (1 H, ¹ J _C,H = 178 Hz, N=CH), 11.75 (br s, 1 H, NH), 14.43 (br s, 1 H, NH); δ (minor isomer) = 2.00 s (3 H, CH₃), 2.66 br s (1 H, SH), 2.85 m (2 H, HSCH ₂ ), 3.30 (m, 2 H, CSCH ₂ ), 8.59 (s, 1 H, ¹ J _C,H = 177 Hz, N=CH), 11.92 (br s, 1 H, NH), 14.61 (br s, 1 H, NH). ¹³C NMR (DMSO-d ₆): δ (major isomer) = 20.3 (CH₃), 23.7 (HSCH₂), 33.7 (CSCH₂), 129.4 (N=CH), 133.4 (CNO₂), 138.2, 146.0, 172.9 (CO); δ (minor isomer) = 21.9 (CH₃), 23.7 (HSCH₂), 33.6 (CSCH₂), 129.3 (N=CH), 133.3 (CNO₂), 138.0, 146.0, 166.4 (CO). HRMS (EI) [M + H]⁺: m/z calcd for C₈H₁₁N₅O₃S₂: 290.0382; found: 290.0376
1,1-Dichloro-3-(imidazolidin-2-ylidene)-3-nitropropan-2-ol ( 20)
Compound 20 was prepared as described for thiazolidine 13; 55% yield; mp 134-136 °C. ¹H NMR (DMSO-d ₆): δ = 3.61 (br s, 4 H, 2 CH₂), 5.14 (d, 1 H, J = 5.1 Hz, CHOH), 6.29 (d, 1 H, J = 5.1 Hz, CHCl₂), 6.70 (br s, 1 H, OH), 8.54 (br s, 2 H, NH). ¹³C NMR (DMSO-d ₆): δ = 43.4 (2 CH₂), 73.9, 75.1 (CHCl₂CH), 106.4 (CNO₂), 159.8 (NHCNH). HRMS (ESI) [M + H]⁺: m/z calcd for C₆H₉Cl₂N₃O₃: 242.0094; found: 242.0095.
1-(2-Chloropyridin-5-ylmethyl)-2-(nitromethyl-ene)imidazolidine ( 21) To a solution of 0.50 g (1.37 mmol) imidazolidine 8 in 20 mL EtOH at 0 °C was added 0.055 g (1.44 mmol) NaBH₄ within 1 min. After 10 min at this temperature, the mixture was diluted with 100 mL cold H₂O and neutralized with 5% HCl. The resulting precipitate was sucked off, washed with H₂O (3 × 20 mL), and dried in vacuo. Imidazolidine 21 was obtained in 60% yield, 0.21 g; mp 163-164 °C (lit. [15] 166-167 °C). ¹H NMR (DMSO-d ₆): δ = 3.58 (m, 4 H, NCH ₂ CH ₂ NH), 4.49 (s, 2 H, CH₂C_aryl), 6.77 (s, 1 H, CHNO₂), 7.54 (d, 1 H, J = 8.1 Hz, H-3_aryl), 7.78 (dd, 1 H, J = 8.1, 1.5 Hz, H-4_aryl), 8.37 (d, 1 H, J = 1.5 Hz, H-6_aryl), 8.90 (br s, 1 H, NH). ¹³C NMR (DMSO-d ₆): δ = 42.7 (NHCH₂), 45.4, 48.2 (CH₂NCH₂), 96.0 (CHNO₂), 124.6 (CH), 131.6 (C_quat), 139.4 (CH), 149.4 (N=CH), 149.8 (CCl), 158.7 (NHCN).
3-(Imidazolidin-2-ylidene)-3-nitro-2-oxopropionitrile ( 22) To a solution of 0.50 g (2.08 mmol) imidazolidine 7 in 10 mL DMF was added 0.81 g (12.46 mmol) NaN₃ in one portion at r.t. After stirring for 1 d, 70 mL cold H₂O was added. On treatment with concd HCl a precipitate appeared that was sucked off and washed with H₂O (2 × 20 mL) and MeOH (2 × 5 mL). Drying in vacuo yielded 0.13 g (35%) 22; mp 255-257 °C. ¹H NMR (DMSO-d ₆): δ = 3.70 (br s, 4 H, 2 × CH₂), 10.03 (br s, 2 H, NH). ¹³C NMR (DMSO-d ₆): δ = 43.5 (2 CH₂), 112.2, 116.3 (CN, CNO₂), 158.0 (NHCNH), 165.0 (C=O). HRMS (ESI) [M + H]⁺: m/z calcd for C₆H₆N₄O₃: 183.0513; found: 183.0513.
1,1-Diazido-3-(1,3-dimethylimidazolidin-2-ylidene)-3-nitropropan-2-one ( 23)
The preparation followed the protocol for 22, but after addition of concd HCl the mixture was extracted with CH₂Cl₂ (6 × 20 mL). The organic layer then was washed with H₂O and dried over CaCl₂. Evaporation of the solvents afforded 0.38 g (75%) azide 23 (starting from 0.50 g, 1.86 mmol of 9), mp 123-125 °C. ¹H NMR (DMSO-d ₆): δ = 2.87 (s, 6 H, 2 × CH₃), 3.91 (br s, 4 H, 2 CH₂), 6.20 (s, 1 H, CH). ¹³C NMR (DMSO-d ₆): δ = 33.8 (2 CH₃), 49.1 (2 CH₂), 75.1 (CH), 107.9 (CNO₂), 161.9 (NCN), 178.2 (C=O). HRMS (ESI) [M + H]⁺: m/z calcd for C₈H₁₁N₉O₃: 282.1058; found: 282.1059.
3-(1,3-Dimethylimidazolidin-2-ylidene)-3-nitro-2-oxo-propionitrile ( 24)
A solution of 0.30 g (1.09 mmol) azide 23 in 10 mL DMF was treated with additional 0.14 g (2.18 mmol) NaN₃ and then was heated to 90-95 °C for 10 h. Work-up as described for 23 gave 0.09 g (40%) nitrile 24; mp 175-177 °C. ¹H NMR (DMSO-d ₆): δ = 2.89 (s, 6 H, 2 CH₃), 3.93 (br s, 4 H, 2 CH₂). ¹³C NMR (DMSO-d ₆): δ = 34.1 (2 CH₃), 49.4 (2 CH₂), 112.6, 115.3 (CN, CNO₂), 159.6 (NCN), 164.2 (C=O). HRMS (ESI) [M + H]⁺: m/z calcd for C₈H₁₀N₄O₃: 211.0826; found: 211.0826.

14 Ol’dekop YA. Kaberdin RV. J. Org. Chem. USSR (Engl. Transl.)  1975,  11:  288 

15 Kagabu S. Yokoyama AK. Iwaya K. Tanaka M. Biosci. Biotechnol. Biochem.  1998,  62:  1216