2- Methoxynaphthalene, demethylation

Scheme 5.1-2 The demethylation of 2-methoxynaphthalene to 2-naphthol with pyridinium chloride.

Selective demethylation of methoxyarenes. Boron trichloride is generally useful for selective cleavage of the more hindered methoxy group of polymethoxybenzenes and of peri-methoxynaphthalenes. 

A novel regiospecific synthesis of islandicin was described by Glein etal. 145) (Scheme 21). Thus Fries rearrangement of l-propionyloxy-5-methoxynaphthalene followed by methylation and bromination yielded the ketone (172). Alkylation with sodium diethyl malonate followed by demethylation, ester hydrolysis and decarboxylation gave the acid (173). Elbs oxidation and sulfuric acid cyclisation of the acid yielded 1-O-methyl-islandicin (174). 

A final synthetic effort in the yohimbine alkaloid area concerns the studies reported by Loewenthal and his coworkers (Scheme 3.92) (143). The aim was to develop an efficient method to prepare the bicyclic enone 21, which serves as a key intermediate in the Woodward reserpine synthesis strategy (19). The route for preparation of 21 began with Friedel Crafts reaction of 2-methoxynaphthalene (523) with the oxalyl chloride equivalent 524, a process which afforded the acenaphthenoquinone 525. Oxidative-decarboxylation of 525 yielded the naphthalene-carboxylic acid 526 which was transformed by Birch reduction and esterification to the dihydro-derivative 527. Carboxyla-tion then provided geminal diester 528 which was epoxidized. Sequential lactonization and methylation afforded tricyclic lactone 529. Ester cleavage with subsequent decarboxylation gave lactone 530 which was demethylated to provide 531. While no further effort was given to the development of this... 

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