Noncovalent Li···H Interaction in the Synthesis of peri-Disubstituted Naphthalene Proton Sponges

Abstract

Noncovalent Li···H interaction was utilised as a tool for the second lithiation of 4-lithio-1,8-bis(dimethylamino)naphthalene with n-BuLi in the presence of TMEDA in hexane. Metallation proceeds with 100% selectivity in the second peri-position and with up to 90% yield. A series of 4,5-disubstituted derivatives of 1,8-bis(dimethylamino)naphthalene has been prepared in good to excellent yield after quenching the reaction mass with different electrophiles.

Combination of “Buttressing” and “Clothespin” Effects for Reaching the Shortest NHN Hydrogen Bond in Proton Sponge Cations

“…It should be noted that our approach to peri-dimethylnaphthalene B2 is more effective than the recently described method using organolithium intermediates. 18 Compound B2 further served as a convenient source for the synthesis of bases C2 (via monobromide C1, Scheme 2a), C3, D1, and D2 (Schemes 2b−c). Some complications arose only when SiMe 3 groups were introduced into the ortho-positions of B2 (Scheme 2c).…”

“…The resulting alcohol 7 upon catalytic hydrogenation in an acidic medium gave compound B2 ; the yield at both stages is close to quantitative. It should be noted that our approach to peri- dimethylnaphthalene B2 is more effective than the recently described method using organolithium intermediates …”

“…MS (EI): m / z = 243 (5), 242 [M] + (31), 227 (4), 196 (30), 182 (22), 150 (18), 128 (40), 112 (49), 105 (73), 104 (52), 83 (32), 77 (25), 57 (100), 55 (41), 44 (57), 43 (73), 42 (59). Other physical and spectral data are consistent with those published in the literature …”

“…Yield 93% (40.5 mg from 32 mg of B2 ); colorless crystals with mp 277–280 °C dec . Crystals suitable for XRD analysis were obtained from a 1:1 mixture of acetonitrile/dichloromethane.…”

“…1 H NMR (400 MHz, CDCl 3 ): δ = 7.34 (d, J = 7.8 Hz, 1 H), 7.17 (d, J = 7.8 Hz, 1 H), 6.81 (d, J = 7.8 Hz, 2 H), 5.08 (s, 2 H), 2.90 (s, 3 H), 2.83 (s, 6 H, NMe 2 ), 2.79 (s, 6 H, NMe 2 ), OH group is not observable. (16), 227 (13), 214 (17), 213 (19), 212 (21), 211 (18), 210 (22), 209 (16), 198 (16), 197 (15), 196 (32), 195 (15), 182 (34), 181 (23), 168 (27), 167 (15), 154 (17), 127 (16), 115 (19) 1,8-Bis(dimethylamino)-4,5-dimethylnaphthalene (B2). Aqueous 37% HBr (1 mL, 6.9 mmol) and 5% Pd−C (0.50 g) were added to a solution of alcohol 7 (1.78 g 6.9 mmol) in methanol (100 mL) and the resulting mixture was agitated in a hydrogen atmosphere for 120 h. After completion of the reaction, the catalyst was filtered off, the solvent was removed, and the remainder was dissolved in aqueous 20% KOH (20 mL).…”