Synlett, Table of Contents Synlett 2013; 24(5): 570-574DOI: 10.1055/s-0032-1318315 letter © Georg Thieme Verlag Stuttgart · New York Selective Methylation of NH-Containing Heterocycles and Sulfonamides Using N,N-Dimethylformamide Dimethylacetal Based on Calculated pK a Measurements Gary Fairley* Astrazeneca, Alderley Park, Macclesfield, Cheshire, SK10 4TG, UK Fax: +44(1625)513253 Email: Gary.Fairley@astrazeneca.com , Catherine Hall Astrazeneca, Alderley Park, Macclesfield, Cheshire, SK10 4TG, UK Fax: +44(1625)513253 Email: Gary.Fairley@astrazeneca.com , Ryan Greenwood Astrazeneca, Alderley Park, Macclesfield, Cheshire, SK10 4TG, UK Fax: +44(1625)513253 Email: Gary.Fairley@astrazeneca.com › Author Affiliations Recommend Article Abstract Buy Article All articles of this category Abstract The use of N,N-dimethylformamide dimethylacetal (DMF-DMA) as a suitable methylating agent for the methylation of NH-containing groups and heterocycles has been investigated. Use of ReactArray and calculated pK a measurements have allowed additional helpful information to be collated to determine optimum reaction conditions for a variety of substrates. Key words Key wordsmethylation - N,N-dimethylformamide dimethylacetal - heterocycles - sulfonamides - pK a Full Text References References and Notes 1 Vorbruggen H. Angew. Chem., Int. Ed. Engl. 1963; 2: 211 2 Priefer R. Tetrahedron Lett. 2011; 52: 2776 3 Abdulla RF, Brinkmeyer RS. Tetrahedron 1979; 35: 1675 4 Watanabe K. J. Heterocycl. Chem. 1977; 14: 537 5 Stanovnik B. Aust. J. Chem. 1981; 34: 1729 6 http://www.alphamultiservicesinc.com/page/442725626. 7 Emiabata-Smith DF, Crookes DL, Owen MR. Org. Process Res. Dev. 1999; 3: 281 8 http://www.acdlabs.com/products/percepta/predictors/pka. 9 Knölker H.-J, Braxmeier T. Tetrahedron Lett. 1996; 37: 5861 10 General Procedure: To a stirred solution of substrate in dry DMF was added DMF-DMA (5 equiv) in one portion at r.t. The resulting mixture was heated at a temperature (60–120 °C) based on calculated pK a (Table 2) for approximately 18 h and allowed to cool to r.t. The reaction mixture was evaporated to dryness and purified by flash silica chromatography. 2-Methyl-4-phenyl-1,2,4-triazol-3-one (4) Temp 70 °C; yield 78%; white solid; MS (ES+): m/z [M + H]+ = 176.33; HPLC: t R= 1.02 min. 1H NMR (700 MHz, DMSO): δ = 8.43 (s, 1 H), 7.67 (dt, J = 8.7, 1.7 Hz, 2 H), 7.48–7.52 (m, 2 H), 7.35–7.38 (m, 1 H), 3.38 (s, 3 H). 13C NMR (176 MHz, DMSO): δ = 151.31, 134.59, 134.11, 129.32, 127.00, 121.48, 32.10. 3-Bromo-N,N-dimethyl-benzenesulfonamide (8) Temp 80 °C; yield 92%; white solid; HRMS: m/z [M + H]+ calcd for C8H10BrNO2S: 263.96939; found: 263.96875. 1H NMR (400 MHz, CDCl3): δ = 7.86 (t, J = 1.8 Hz, 1 H), 7.62–7.69 (m, 2 H), 7.35 (t, J = 7.9 Hz, 1 H), 2.67 (s, 6 H). 1-Methyl-3-phenyl-1H-pyrrolo[2,3-c]pyridine (11) Temp 100 °C; yield 73%; beige solid; MS (ES+): m/z [M + H]+ = 209.41. HPLC: t R = 2.13 min. 1H NMR (400 MHz, DMSO): δ = 8.90 (s, 1 H), 8.23 (d, J = 5.6 Hz, 1 H), 7.95 (s, 1 H), 7.83 (dd, J = 5.6, 1.0 Hz, 1 H), 7.69 (dd, J = 8.3, 1.2 Hz, 2 H), 7.46 (t, J = 7.8 Hz, 2 H), 7.27 (t, J = 7.4 Hz, 1 H), 3.97 (s, 3 H). 13C NMR (101 MHz, DMSO, 30 °C): δ = 138.71, 134.37, 134.12, 133.72, 131.18, 129.26, 128.87, 126.21, 125.70, 114.23, 113.58, 32.79. 1-Methyl-3-phenylindole (13) Temp 120 °C; yield 87%; colorless gum; HRMS: m/z [M + H]+ calcd for C15H13N: 207.1048; found: 207.1027. 1H NMR (400 MHz, DMSO): δ = 7.88 (d, J = 8.0 Hz, 1 H), 7.64–7.7 (m, 3 H), 7.50 (d, J = 8.2 Hz, 1 H), 7.40–7.47 (m, 2 H), 7.20–7.27 (m, 2 H), 7.11–7.17 (m, 1 H), 3.85 (s, 3 H).
