Synlett 2013; 24(19): 2515-2518
DOI: 10.1055/s-0033-1339339
cluster
© Georg Thieme Verlag Stuttgart · New York

Synthesis of 2-Alkynyl-, 4-Alkynyl-, and 2,7-Dialkynyl-1,8-bis(dimethyl­amino)naphthalenes and the Unexpected Influence of ortho-Alkynyl Groups on Their Basicity

Ekaterina A. Filatova
Department of Organic Chemistry, Southern Federal University, Zorge 7, 344090 Rostov-on-Don, Russian Federation   Fax: +7(863)2975146   Email: apozharskii@sfedu.ru
,
Alexander F. Pozharskii*
Department of Organic Chemistry, Southern Federal University, Zorge 7, 344090 Rostov-on-Don, Russian Federation   Fax: +7(863)2975146   Email: apozharskii@sfedu.ru
,
Anna V. Gulevskaya
Department of Organic Chemistry, Southern Federal University, Zorge 7, 344090 Rostov-on-Don, Russian Federation   Fax: +7(863)2975146   Email: apozharskii@sfedu.ru
,
Nikolay V. Vistorobskii
Department of Organic Chemistry, Southern Federal University, Zorge 7, 344090 Rostov-on-Don, Russian Federation   Fax: +7(863)2975146   Email: apozharskii@sfedu.ru
,
Valery A. Ozeryanskii
Department of Organic Chemistry, Southern Federal University, Zorge 7, 344090 Rostov-on-Don, Russian Federation   Fax: +7(863)2975146   Email: apozharskii@sfedu.ru
› Author Affiliations
Further Information

Publication History

Received: 31 May 2013

Accepted after revision: 11 June 2013

Publication Date:
17 July 2013 (online)


Abstract

Novel 2-alkynyl-, 4-alkynyl-, and 2,7-dialkynyl derivatives of 1,8-bis(dimethylamino)naphthalene (‘proton sponge’) have been synthesized and their basicity values have been measured by competitive NMR studies in DMSO. These indicate that, while the para-alkynyl groups decrease the basicity of the parent proton sponge approximately by one order of magnitude in accordance with their electron-accepting nature, the influence of ortho-alkynyl functionalities is unexpectedly base-enhancing. The latter phenomenon has been ascribed to the appearance of a buttressing effect, but some other factors can be also at work.

Supporting Information

 
  • References and Notes

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  • 13 1,8-Bis(dimethylamino)-2-(phenylethynyl)naphthalene (6a) Yellow solid; mp 98–100 °C (from EtOH). 1H NMR (250 MHz, CDCl3): δ = 2.78 (6 H, s, NMe2), 3.16 (6 H, s, NMe2), 6.95 (1 H, dd, J = 6.0, 2.8 Hz, Harom), 7.28–7.40 (7 H, m, Harom), 7.54 (2 H, dd, J = 7.7, 1.8 Hz, Harom). 13C NMR (62.9 MHz, CDCl3): δ = 45.0, 45.2, 91.5, 94.5, 114.2, 114.7, 122.0, 123.0, 124.8, 126.8, 128.0, 128.8, 131.0, 131.3, 138.2, 152.0, 152.5. MS: m/z (%) = 314 (90) [M]+, 299 (24), 282 (72), 268 (77), 254 (29), 226 (35), 207 (37), 196 (27), 167 (26), 157 (25), 149 (29), 141 (29), 133 (25), 127 (53), 113 (38), 103 (26), 91 (70), 77 (68), 58 (72), 51 (35). 44 (100). Anal. Calcd for C22H22N2: C, 84.04; H, 7.05; N, 8.91. Found: C, 83.87; H, 7.23; N, 9.03. 1,8-Bis(dimethylamino)-2-(p-tolylethynyl)naphthalene (6b) Yellow solid; mp 89–92 °C (from EtOH). 1H NMR (250 MHz, CDCl3): δ = 2.37 (3 H, s, CMe), 2.79 (6 H, s, NMe2), 3.18 (6 H, s, NMe2), 6.95 (1 H, dd, J = 6.3, 2.4 Hz, Harom), 7.16 (2 H, d, J = 8.1 Hz, p-Tol), 7.24–7.40 (4 H, m, Harom), 7.43 (2 H, d, J = 8.1 Hz, 4-Tol). 13C NMR (62.9 MHz, CDCl3): δ = 22.0, 45.0, 45.2, 91.0, 94.8, 114.0, 115.0, 119.2, 121.8, 122.1, 123.0, 126.8, 129.8, 131.0, 131.2, 138.2, 138.3, 152.0, 152.1. MS: m/z (%) = 328 (100) [M]+, 313 (25), 296 (74), 282 (66), 268 (17), 206 (18), 196 (20), 164 (21), 149 (22), 141 (17), 134 (18), 127 (20). Anal. Calcd for C23H24N2: C, 84.11; H, 7.37; N, 8.53. Found: C, 84.24; H, 7.26; N, 8.37. 1,8-Bis(dimethylamino)-2-(trimethylsilylethynyl)-naphthalene (6c) Dark yellow oil. 1H NMR (250 MHz, CDCl3): δ = 0.25 (9 H, s, SiMe3), 2.78 (6 H, s, NMe2), 3.09 (6 H, s, NMe2), 6.91 (1 H, m, Harom), 7.24–7.35 (4 H, m, Harom). 13C NMR (62.9 MHz, CDCl3): δ = 0.5, 45.0, 45.1, 82.4, 99.1, 107.3, 114.0, 122.0, 122.7, 126.8, 131.3, 138.4, 138.5, 152.1, 153.1. IR: 2140 (C≡C), 1553 (ring) cm–1. MS: m/z (%) = 310 (51) [M]+, 295 (29), 279 (24), 264 (22), 238 (30), 221 (17), 206 (51), 192 (30), 73 (100). Anal. Calcd for C19H26N2Si: C, 73.49; H, 8.44; N, 9.02. Found: C, 73.58; H, 8.29; N, 9.23. 2-Ethynyl-1,8-bis(dimethylamino)naphthalene (6d) Dark yellow oil. 1H NMR (250 MHz, CDCl3): δ = 2.86 (6 H, s, NMe2), 3.20 (6 H, s, NMe2), 3.45 (1 H, s, ≡CH), 7.04 (1 H, m, Harom), 7.31–7.45 (4 H, m, Harom). 13C NMR (62.9 MHz, CDCl3): δ = 45.0, 45.2, 82.4, 85.6, 113.6, 114.2, 122.1, 122.9, 123.0, 126.9, 131.4, 138.5, 152.1, 153.3. IR: 3303 (≡CH), 2093 (C≡C), 1600, 1553 (ring) cm–1. MS: m/z (%) = 238 (95) [M]+, 223 (18), 206 (70), 192 (83), 178 (21), 165 (18), 152 (31), 139 (15), 111 (21), 103 (23), 89 (25), 76 (33), 63 (34), 58 (69), 32 (100). Anal. Calcd for C16H18N2: C, 80.63; H, 7.61; N, 11.75. Found: C, 80.50; H, 7.79; N, 11.81. 1,8-Bis(dimethylamino)-2,7-bis(phenylethynyl)-naphthalene (7a) Yellow solid, mp 156–157 °C (from EtOH or n-octane). 1H NMR (250 MHz, CDCl3): δ = 3.20 (12 H, s, 2 NMe2), 7.33–7.47 (10 H, m, Harom), 7.55–7.62 (4 H, m, Harom). 13C NMR (62.9 MHz, CDCl3): δ = 45.0, 91.0, 94.5, 117.0, 123.5, 124.4, 126.3, 128.0, 128.5, 131.0, 131.5, 138.0, 153.0. IR: 2211 (C≡C) cm–1. MS: m/z (%) = 414 (94) [M]+, 399 (39), 382 (100), 368 (31), 307 (25), 91 (29), 58 (23). Anal. Calcd for C30H26N2: C, 86.92; H, 6.32; N, 6.76. Found: C, 87.09; H, 6.17; N, 6.84. 1,8-Bis(dimethylamino)-2,7-bis(p-tolylethynyl)-naphthalene (7b) Yellow-orange solid, mp 155–156 °C (from i-PrOH). 1H NMR (250 MHz, CDCl3): δ = 2.36 (6 H, s, 2 CMe), 3.15 (12 H, s, 2 NMe2), 7.17 (4 H, d, J = 7.9 Hz, 4-Tol), 7.32 (2 H, d, J = 8.5 Hz, Harom), 7.40 (2 H, d, J = 8.5 Hz, Harom), 7.43 (4 H, d, J = 7.9 Hz, 4-Tol). 13C NMR (62.9 MHz, CDCl3): δ = 22.0, 45.0, 90.5, 95.0, 117.5, 121.5, 124.0, 126.8, 129.5, 131.5, 131.8, 138.0, 138.5, 153.0. IR: 2210 (C≡C) cm–1. MS: m/z (%) = 442 (100) [M]+, 427 (40), 410 (89), 396 (33), 320 (22), 221 (20), 205 (21), 191 (17), 175 (26). Anal. Calcd for C32H30N2: C, 86.84; H, 6.83; N, 6.33. Found: C, 87.00; H, 6.95; N, 6.23. 1,8-Bis(dimethylamino)-2,7-bis(trimethylsilylethynyl)-naphthalene (7c) Dark yellow oil. 1H NMR (250 MHz, CDCl3): δ = 0.24 (18 H, s, 2 SiMe3), 3.06 (12 H, s, 2 NMe2), 7.20 (2 H, d, J = 8.5 Hz, Harom), 7.27 (2 H, d, J = 8.5 Hz, Harom). IR: 2133 (C≡C), 1525 (ring) cm–1. Anal. Calcd for C24H34N2Si2: C, 70.88; H, 8.43; N, 6.89. Found: C, 71.04; H, 8.54; N, 6.71. 2,7-Diethynyl-1,8-bis(dimethylamino)naphthalene (7d) Yellow oil. 1H NMR (250 MHz, CDCl3): δ = 3.09 (12 H, s, 2 NMe2), 3.37 (1 H, s, ≡CH), 7.27 (2 H, d, J = 8.9 Hz, Harom), 7.33 (2 H, d, J = 8.95 Hz, Harom). 13C NMR (62.9 MHz, CDCl3): δ = 45.2, 83.0, 85.0, 115.8, 123.6, 126.1, 132.5, 138.4, 154.0. IR: 3300 (≡CH), 2090 (C≡C), 1540 (ring) cm–1. MS: m/z (%) = 262 (100) [M]+, 230 (59), 216 (41). Anal. Calcd for C18H18N2: C, 82.41; H, 6.92; N, 10.68. Found: C, 82.62; H, 6.71; N, 10.78. 1,8-Bis(dimethylamino)-4-(phenylethynyl)naphthalene (8a) Yellow solid; mp 147–149 °C (from EtOH). 1H NMR (250 MHz, CDCl3): δ = 2.80 (6 H, s, NMe2), 2.85 (6 H, s, NMe2), 6.87 (1 H, d, J = 8.0 Hz, Harom), 6.97 (1 H, d, J = 7.7 Hz, Harom), 7.31–7.41 (4 H, m, Harom), 7.58–7.67 (3 H, m, Harom), 8.04 (1 H, d, J = 8.3 Hz, Harom). 13C NMR (62.9 MHz, CDCl3): δ = 44.3, 44.5, 89.6, 93.1, 111.9, 112.9, 113.3, 119.9, 120.6, 124.7, 126.8, 128.1, 128.7, 131.1, 131.8, 138.1, 151.5, 151.9. IR: 2201 (C≡C) cm–1. MS: m/z (%) = 314 (100) [M]+, 299 (19), 283 (44), 268 (76), 226 (21), 134 (13). Anal. Calcd for C22H22N2: C, 84.04; H, 7.05; N, 8.91. Found: C, 83.92; H, 7.21; N, 9.10. 1,8-Bis(dimethylamino)-4-(p-tolylethynyl)naphthalene (8b) Yellow solid; mp 94–96 °C (from EtOH). 1H NMR (250 MHz, CDCl3): δ = 2.36 (3 H, s, CMe), 2.78 (6 H, s, NMe2), 2.82 (6 H, s, NMe2), 6.84 (1 H, d, J = 8.0 Hz, Harom), 6.95 (1 H, dd, J = 7.7, 1.1 Hz, Harom), 7.16 (2 H, d, J = 8.1 Hz, Harom), 7.39 (1 H, dd, J = 7.7, 8.1 Hz, Harom), 7.49 (2 H, dm, J = 8.1 Hz, Harom), 7.57 (1 H, d, J = 8.0 Hz, Harom), 8.00 (1 H, dd, J = 8.1, 1.1 Hz, Harom). 13C NMR (62.9 MHz, CDCl3): δ = 21.9, 44.4, 44.5, 88.8, 93.2, 112.0, 113.3, 119.8, 119.9, 120.0, 121.6, 126.7, 129.5, 130.9, 131.7, 138.0, 138.1, 151.4, 151.7. IR: 2140 (C≡C) cm–1. MS: m/z (%) = 328 (100) [M]+, 313 (19), 297 (44), 284 (38), 268 (14), 239 (18), 149 (21), 140 (30), 134 (14), 127 (13). Anal. Calcd for C23H24N2: C, 84.11; H, 7.37; N, 8.53. Found: C, 84.28; H, 7.15; N, 8.46. 1,8-Bis(dimethylamino)-4-(trimethylsilylethynyl)-naphthalene (8c) Yellow solid; mp 108–109 °C (from MeOH). 1H NMR (250 MHz, CDCl3): δ = 0.27 (9 H, s, SiMe3), 2.74 (6 H, s, NMe2), 2.79 (6 H, s, NMe2), 6.77 (1 H, d, J = 8.0 Hz, Harom), 6.91 (1 H, dd, J = 7.6, 1.1 Hz, Harom), 7.36 (1 H, dd, J = 7.6, 8.2 Hz, Harom), 7.51 (1 H, d, J = 8.0 Hz, Harom), 7.88 (1 H, dd, J = 8.2, 1.1 Hz, Harom). 13C NMR (62.9 MHz, CDCl3): δ = 0.7, 44.3 44.4, 97.5, 105.3, 111.6, 112.7, 113.2, 119.6, 119.8, 126.8, 131.5, 138.2, 151.4, 152.0. IR: 2144 (C≡C) cm–1. Anal. Calcd for C19H26N2Si: C, 73.49; H, 8.44; N, 9.02. Found: C, 73.41; H, 8.27; N, 9.19. 4-Ethynyl-1,8-bis(dimethylamino)naphthalene (8d) Dark yellow oil. 1H NMR (250 MHz, CDCl3): δ = 2.76 (6 H, s, NMe2), 2.81 (6 H, s, NMe2), 3.36 (1 H, s, ≡CH), 6.79 (1 H, d, J = 7.9 Hz, Harom), 6.92 (1 H, dm, J = 7.6 Hz, Harom), 7.37 (1 H, dd, J = 7.6, 8.2 Hz, Harom), 7.54 (1 H, d, J = 8.0 Hz, Harom), 7.90 (1 H, dd, J = 8.2, 1.0 Hz, Harom). 13C NMR (62.9 MHz, CDCl3): δ = 44.3, 44.4, 80.5, 83.8, 105.3, 111.6, 113.3, 119.6, 121.9, 126.9, 131.9, 138.3, 151.5, 152.2. IR: 2085 (C≡C), 3290 (≡CH) cm–1. Anal. Calcd for C16H18N2: C, 80.63; H, 7.61; N, 11.75. Found: C, 80.74; H, 7.47; N, 11.59. For general procedures and other experimental and analytical details see the Supporting Information.
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