1- Naphthalenethiol

Partial reduction of polyarenes has been reported. Use of boron trifluoride hydrate (BF3 OH2) as the acid in conjunction with triethylsilane causes the reduction of certain activated aromatic systems 217,262 Thus, treatment of anthracene with a 4-6 molar excess of BE3 OH2 and a 30% molar excess of triethylsilane gives 9,10-dihydroanthracene in 89% yield after 1 hour at room temperature (Eq. 120). Naphthacene gives the analogously reduced product in 88% yield under the same conditions. These conditions also result in the formation of tetralin from 1-hydroxynaphthalene (52%, 4 hours), 2-hydroxy naphthalene (37%, 7 hours), 1-methoxynaphthalene (37%, 10 hours), 2-methoxynaphthalene (26%, 10 hours), and 1-naphthalenethiol (13%, 6 hours). Naphthalene, phenanthrene, 1-methylnaphthalene, 2-naphthalenethiol, phenol, anisole, toluene, and benzene all resist reduction under these conditions.217 Use of deuterated triethylsilane to reduce 1-methoxynaphthalene gives tetralin-l,l,3-yielding information on the mechanism of these reductions.262 2-Mercaptonaphthalenes are reduced to 2,3,4,5-tetrahydronaphthalenes in poor to modest yields.217 263... 

Mixture of 62.82% dipropylene glycol, 21.18% mercaptoacetic acid, 6% n-hexanoic acid, 6% N-methyl morpholine, 2.18% p-cresyl isovalerate, 0.91% 2-naphthalenethiol, and 0.91% skatole. 

B. 2-Naphthalenethiol. In a 250-ml. flask, fitted with a diffusion tube2 and swept with nitrogen, is placed 23.1 g. (0.10 mole) of O-2-naphthyldimethylthiocarbamate (Note 4). The flask is heated at 270-275° for 45 minutes in a salt bath (Note 5). After cooling, a solution of 8.4 g. (0.15 mole) of potassium hydroxide in 10 ml. of water and 75 ml. of ethylene glycol is added to the flask. The diffusion tube is replaced by a condenser, and the mixture is heated at reflux for 1 hour (Note 6). The cooled reaction mixture is poured onto 150 g. of ice. After the ice has melted, the mixture is shaken two times with 150-ml. portions of chloroform. The chloroform layers are discarded, and the aqueous layer is cautiously acidified with concentrated hydrochloric acid (Note 7) and shaken three times with 75-ml. portions of chloroform. The organic layers are combined and dried by filtration through anhydrous magnesium sulfate. The solvent is removed by distillation to yield 13-15 g. of crude product. Distillation yields 10.3-12.8 g. (71-80%) of pure 2-naphthalenethiol, b.p. 92-94° (0.4 mm.), m.p. 80-81° (Note 8). 

Previous preparations of 2-naphthalenethiol have included reduction of 2-naphthylsulfonyl chloride with zinc and acid4,5 or phosphorus and iodine.6-7 Alternatively, 2-naphthyldia-zonium chloride has been converted to the thiol using potassium ethyl xanthate and sodium carbonate.8 1 2 3 4... 

Aromatic rings can also trap aryl radicals in the propagation cycle of the S l mechanism to give ring closure product. The reaction of o-dihalobenzenes 341 with 2-naphthalenethiolate ion (342) in liquid ammonia under photostimulation gives the ring closure product 343 as well as the substitution product 344 (equation 201 )344. 

A potentially useful one-pot procedure for the conversion of suitable aryl thiols to benzo[6]thiophenes or napththo[2,l-6]thiophenes in the presence of silica supported acidic and basic reagents has been devised, as exemplified by the synthesis of the system 9 from 2-naphthalenethiol 10 <05SL2739>. A stepwise variant of the same theme has been employed in a synthesis of 6-bromo-l,2,3,4-tetrahydrodibenzothiophene, a partner for a Suzuki coupling leading to a chromene-4-one containing inhibitor of DNA-dependent protein kinase <05JMC7829>. 

S-2-Naphthyl dimethylthiocarbamate, hydrolysis with potassium hydroxide to 2-naphthalenethiol,... 

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