Thiophenes 2,4-diamino- from

Diamino-3,4-dicyanothiophene is thus converted by NaOH to 2-amino-3,4-dicyano-5-mercaptopyrrole (Scheme 132) (58JA2822). Here, prior to the recyclization of the intermediate (396), a rotation around the 4,5-bond has occurred. With other substrates such as (397), recyclization results in a thiophene, different from the precursor. Here the 3-substituent is involved in the cyclization and so a rotation around the 3,4-bond is mandatory. One can therefore postulate an intermediate of the type (398) in such reactions ring closure of this will lead to a thiophene-3-carbonitrile which could be either (399) or (400). Some examples are shown in Scheme 133 (75JPR861, 77JCR(S)294). 

Thiophene aldehydes have been used earlier for the construction of macrocyclic Schiff bases <81CC628>. An example is the synthesis of the macrocyclic tetraimine Schiff base (479) from thiophene 2,5-dicarbaldehyde and l,3-diamino-2-hydroxypropane <87JCS(D)219>. The synthesis does not involve use of a metal template. An interesting extension is the synthesis of the macrocyclic Schiff base (481) containing four thiophene units from the dialdehyde (480) <89BCJ1346>. The condensation is achieved at room temperature in CHCI3. 

On the basis of the formal similarity between 1,8-diamino-naphthalene and 3,4-diaminothienothiophene (1) the latter might be able to form a fused pyrimidine system on reaction with orthoformic ester or formamide. However, heating dimethyl 3,4-diaminothieno[2,3-6]-thiophene-2,5-dicarboxylate with acetic anhydride gave the corresponding MiV -diacetyl derivative, while 3,4-diacyloxy derivatives resulted from analogous reaction of dimethyl 3,4-dihydroxythieno-[2,3-6]thiophene-2,5-dicarboxylate with orthoformic ester and acetic anhydride."... 

A tetrasubstituted thiophene 291 with a catalytic amount of base gave 3,4-diamino-A, A -dicyanothieno [2,3- ]thiophene-2,5-dicarboximidamide 292, from which, by heating in methanol in the presence of HCl, l,3,6,8-tetraaminopyrimido[4",5" 4, 5 ]thieno[3, 2 4,5]thieno-[2,3- pyrimidine 293 was prepared (Scheme 29) <1996T1011>. 

Aminobenzo[6]thiophene is prepared from 7-hydroxybenzo[6]-thiophene by means of the Bucherer reaction it may be converted into 7-nitrobenzo[6]thiophene via the diazonium salt.84 5,7-Diamino-3-phenylbenzo[6]thiophene and its 2-carboxylic acid are prepared by reduction of the corresponding dinitro compound.334 Partial reduction of o,7-dinitro-3-phenylbenzo[6]thiophene-2-carboxylic acid with ethanolic ammonium sulfide affords 7-amino-5-nitro-3-phenylbenzo-[6]thiophene-2-carboxylic acid, the amino group of which may be replaced by hydrogen or iodine via the diazonium salt.334 7-Amino-4-methoxybenzo[6]thiophene is mentioned in the patent literature.560... 

Another way was tried with condensation polymers (41) and (42) obtained from 2,5-diamino-3,4-dicyanthiophen and terephthalic add dichloride or thiophen-2,5-dicarboxal-dehyd . Heating (41) ami (42) with 1,2-dicyanobenzene and Cu(II)-salts at 473-523 K the corresponding phthalocyanines (43), (44) were obtained (Eq. 16). According to IR, elementary analysis and hydrolysis every second unit contains a phthalot anine system. 

The oxidative ring-closure of (178) gave (179), and similarly (180) was obtained from 3,4-diamino-2,5-dithiocarbamino-thieno[2,3-6]thiophen. The synthesis of substituted (3//)-thieno[2,3-rf]imidazoles has been achieved by a Curtius rearrangement of (181). ... 

Miscellaneous Rings containing Several Nitrogens.—From 4,5-diamino-benzo[A]thiophen and its 3-methyl derivative, the ring system (620) was obtained by condensation with 9,10-phenanthrenequinone, and the system... 

Aminothien-4-yl pyridinium iodides (52), readily prepared from 1-cyano-methylpyridinium chloride (51) and carbon disulphide, on successive treatment with methyl iodide, methylamine, and 10% hydrochloric acid, afford ultimately 3,4-diamino-thiophens (53) in >80% yield, via the sequence of reactions outlined in Scheme 11. ... 

In the reaction of ethyl cyanoacetate with sulphur and base, 2,4-diamino-3,S-di(ethoxycarbonyl)thiophen was only the minor product (20%). The major products were pyrrole derivatives. From cyanoacetamide and benzyl cyanide no thiophen derivatives were obtained. The reaction of (9a) with (10) in the presence of triethylamine yields the aminothiophen (11), while (9b) gives the hydroxy thiophen (12). If the salt of ethyl (thiobenzoyl)... 

Contrary to benzo[b]thiophen, benzo[b]selenophen is acylated at position 2. 2-Bromobenzo[b]selenophen, prepared from the 2-lithium derivative and bromine, is acylated at position 3, and from this derivative the 3-isomers could be synthesized. A large number of 2- and 3-aroylbenzo[b]seleno-phens were synthesized, either by Friedel-Crafts reaction of benzo-[bjselenophencarboxylic acid chlorides and benzenes or from benzol bjselenophens and benzoic acid chlorides. Also the reaction between Grignard reagents and nitriles was used for the synthesis of aroylbenzo[b]selenophens. 4,S-Diaminobenzo[b]selenophen has been synthesized via nitration of 5-aminobenzo[b]selenophen or via the reaction of the diazonium salt derived from the S-amino-derivative with p-sulphanilic acid. From the diamino-derivative, several fused benzo[b]selenophens, e.g. (525), (526), and (527), were prepared. Reaction of the phenyl-... 

---