Benzothieno benzothiophene synthesis

This approach is used for the syntheses of fused heterocycles which have a [l,3]-heteroatom juxtaposition in one of the rings <1996CHEC-II(7)49>. The unambiguous synthesis of tetrahydro-3//-benzothieno[2,3- / imidazole 87, as a target for the potential treatment of anxiety disorders, was accomplished starting from commercially available ethyl 2-amino-4,5,6,7-tetrahydro-benzothiophene-3-carboxylate 85 the key formation of the bicyclic heterocycle occurred through a final acid-mediated cyclization of 86 (Scheme 17) <1997SC473>. 

This strategy is used mostly for the synthesis of annelated pyrazoles in which the second reactant has two electrophilic sites in a 1,3-juxtaposition. Under control conditions, the first synthesis of a 3-aminopyrrolo[2,3-d]pyrazole (129) was realized from ethyl(3-cyano-4,5-diphenyl-pyrrolylthio)acetate (128) (Scheme 18) <91T8243>. The synthesis of the benzothieno[3,2-c]pyrazole (131) occurred as a two-step process with initial SNAr addition of hydrazine to the chloro-benzothiophene 5,5-dioxide (130) (Equation (42)) <74LA1248>. 

The scope of the reaction was probed by extending the reaction to the synthesis of six-membered cyclic sulphamides. The reaction of 367 with acetamidine gave 1,2,4,6-thiatriazinone-1,1-dioxides 371 (equation 121) in yields of 20%. Fragmentation of the intermediates prior to cyclization is considered to account for the low yields. Modest yields of the pyridothiatriazinone 372 were obtained by condensation of aminopyridine with 367 (equation 122). Aminotriazoles when reacted with 367 yielded the triazolothiatriazinones 373 (equation 123). The reaction of 2-amino-3-ethoxycarbonyl 4,5,6,7-tetrahydro-l-benzothiophen (374) with isopropyl sulphamoyl chloride gives the iV-(isopropyl)-iV -(3-ethoxycarbonyl-4,5,6,7-tetrahydro-l-benzothiophene)sulphamide (375)369. Cyclization of 375 with 5% sodium hydroxide leads to the formation of the cyclic sulphamide 3-isopropyl-4-oxo-3,4,5,6,7,8-hexahydro-1H [ 1 ] -benzothieno [2,3-d] -2,1,3-thiadiazin-2,2-dioxide (376) in 42% yield. Decarboxylation of 375 also occurs in the reaction with the formation of iV-(isopropyl)-iV -(4,5,6,7-tetrahydro-l-benzothiophene)sulphamide 377... 

Amide-directed metallation-transmetallation enables allylation to be achieved in the 3-position of the naphthalene derivative 23, cyclisation of which yields the naphtho[2,3-c]pyran-l-one (Scheme 23). Application of similar methodology to benzothiophene afforded the [l]benzothieno[2,3-c]pyran system <01TL5955>. Directed ortho metallation also features in a synthesis of 4-arylisochroman-3-ols <01TL9293>. 

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