· (MW 214.31)
(used as weakly nucleophilic strong base)
Alternate Name: Proton Sponge®.
Physical Data: mp 49-51 °C (45-46 °C).3
Solubility: sol most organic solvents.
Form Supplied in: yellow-tan crystals.
Preparative Method: prepared in 82% yield from 1,8-diaminonaphthalene, dimethyl sulfate, and sodium hydride.3
Purification: recrystallized from petroleum ether.3
Handling, Storage, and Precautions: irritant.
The strong basic properties of 1,8-bis(dimethylamino)naphthalene (1) are attributed to a combination of dipole-dipole repulsions (nitrogen lone pairs), van der Waals repulsions, and steric inhibition of resonance.4 Relief of strain imposed by the close proximity of the nitrogen lone pairs occurs upon protonation, giving this base one of the highest pK
a values of the aromatic amines (pK a 12.1; pK a of N,N-dimethylaniline 5.1). A variety of stronger Proton Sponge-like aromatic amine bases, such as the 2,7-dimethoxy derivatives (2) and (3)5 and the bis(dimethylamino)fluorenyl system (4),6 have been prepared and exhibit pK a values of 16.1, 16.3, and 13.5, respectively. However, it is observed in these types of systems that the rates of proton transfer to and from the
amine base are very slow.7
The weak nucleophilic character of (1) makes this reagent useful for applications involving the neutralization of acid in systems sensitive to Lewis basic reagents. In the phosphorylation of 5-vinyl- and 5-ethynyl-2´-deoxyuridines to the corresponding 5´-triphosphates (eq 1),8 Proton Sponge effectively promotes formation of the intermediate phosphorodichloridate whereas other bases (TEA, i-Pr2EtN, collidine, DBU, DBN) are ineffective. A phosgene-free synthesis of highly pure isocyanates from carboxylic acids and Diphenyl Phosphorazidate occurs in good yields only with (1) as base (eq 2).9 Other tertiary amine bases give lower yields and contaminate the product after distillation. The oxidative decarboxylation-deoxygenation
of 3-hydroxycarboxylic acids to tri- and tetrasubstituted alkenes (eq 3) makes use of Proton Sponge to eliminate acid-catalyzed alkene isomerization or degradation of the products,10,11 and the Tin(II) Trifluoromethanesulfonate-promoted addition of aliphatic 1-alkynes to aldehydes (eq 4) proceeds best when performed with this nonnucleophilic base.12
1,8-Bis(dimethylamino)naphthalene has particular value in applications involving the use of transition metal catalysts. Its use in palladium-catalyzed arylations (eq 5),13,14 alkoxycarbonylation (eq 6),15 and intramolecular cyclizations16 is noteworthy, giving superior yields compared to other more nucleophilic bases.
- 1. Alder, R. W. CRV 1989, 89, 1215.
- 2. Staab, H. A.; Saupe, T. AG(E) 1988, 27, 865.
- 3. Quast, H.; Risler, W.; Döllscher, G. S 1972, 558.
- 4. Alder, R. W.; Bowman, P. S.; Steele, W. R. S.; Winterman, D. R. CC 1968, 723.
- 5. (a) Alder, R. W.; Goode, N. C.; Miller, N.; Hibbert, F.; Hunte, K. P. P.; Robbins, H. J. CC 1978, 89. (b) Hibbert, F.; Hunte, K. P. P. JCS(P2) 1983, 1895.
- 6. Staab, H. A.; Saupe, T.; Krieger, C. AG(E) 1983, 22, 731.
- 7. Hibbert, F. ACR 1984, 17, 115.
- 8. Kovács, T.; &OOuml;tvös, L. TL 1988, 29, 4525.
- 9. Gilman, J. W.; Otonari, Y. A. SC 1993, 23, 335.
- 10. Meier, I. K.; Schwartz, J. JACS 1989, 111, 3069.
- 11. Tanzawa, T.; Schwartz, J. TL 1992, 33, 6783.
- 12. Yamaguchi, M.; Hayashi, A.; Minami, T. JOC 1991, 56, 4091.
- 13. Badone, D.; Guzzi, U. TL 1993, 34, 3603.
- 14. Ozawa, F.; Kubo, A.; Hayashi, T. TL 1992, 33, 1485.
- 15. Stille, J. K.; Wong, P. K. JOC 1975, 40, 532.
- 16. Mori, M.; Kubo, Y.; Ban, Y. TL 1985, 26, 1519.
Bruce A. Barner
Union Carbide Corporation, South Charleston, WV, USA
Copyright © 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.