6.7- Dimethoxy-2-naphthoic acid

Dimethoxy-3,4-dihydro-2-naphthoic acid can be dehydrogenated to give 6,7-dimethoxy-2-naphthoic acid. The yield of the latter was 85% after distillation and crystallization from alcohol. 

DIMETHOXY-3,4-DIHYDRO-2-NAPHTHOIC ACID (2-Naphthoic acid, 3,4-dihydro-6,7-dimethoxy-)... 

In a procedure for the synthesis of 6,7-dimethoxy-3,4-dihydro-2-naphthoic acid (IV) by the method of G. P. Crowley and R. Robinson, ethyl y-veratrylbutyrate (I) is formylated with ethyl formate by dropwise addition of a solution of 1 and ethyl formate in ether to a suspension of sodium ethoxide in ether at —10°. After acidification, the formyl derivative II is collected by ether extraction and cyclized to III with a mixture of 90% phosphoric acid and concentrated sulfuric acid at 0-10°. Saponification gives the acid IV, m.p. 193°. 

Figure 3.93 Proposed biosynthetic pathway for the kedarcidin chromophore. (a) 3-Hydroxy-7,8-dimethoxy-6-isopropoxy-2-naphthoic acid from 3,6,8-trihydroxy-2-naphthoic acid, (b) Enediyne core from acetate and convergent assembly of the four components to give kedarcidin chromophore 302.

A soln. of N-n-butyl-4, 5 -dimethoxy-2 -nitro-2-naphthanilide in ethanol-water irradiated 40 hrs. with filtered sunlight of 2 > 370 nm -> 2-naphthoic acid. Y 92%. F. e. by irradiation with 3500 A lamps s. B. Amit and A. Patdiornik, Tetrah. Let. 1973, 2205. 

A mixture of 2-(3,5-dimethoxybenzyl) succinic acid and acetic anhydride refluxed 20 min., excess acetic anhydride removed under reduced pressure, poly-phosphoric acid added to the residue, and heated 2 hrs. with stirring on a steam hath 4-oxo-5,7-dimethoxy-l,2,3,4-tetrahydro-2-naphthoic acid. Y 73.5%. Z. Horii, T. Katagi, and Y. Tamura, Ghem. Pharm. Bull. 11, 309 (1963) ring closure s. a. R. Quelet, R. Dran, and G. Lukacs, G. r. 258, 2590 (1964). 

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