Miscellaneous Fused Systems

Finally, some miscellaneous fused systems containing thiophene rings have attracted some interest. The electrophilic chemistry of several thia-PHAs has been investigated, among others benzo[Z>]naphtho[2,l-c/]thiophene , whereas an approach to related partially saturated systems from tetrahydrothiophene-3-one has been published <07TL4715>. It should also be mentioned that a 4-armno-7-ar ithieno 3,2-<7 pyrimidine library has been prepared <07JCC431>. 

Miscellaneous Fused Systems.-An elegant synthesis of thieno[2,3-c ]-pyridazine in 40% yield consists of heating thiophen-2-carbaldehyde azine with AlCla-triethylamine at 170-200°C. 2,3-Dimethylthieno[3,4-i>]-pyrazine has been prepared from 2,4-diaminothiophen. A derivative of the unusual thienopterine (303 R = OH) that was isolated from human urine in 1940, namely (303 R = H), has been synthesized from 2-amino-3,5-dicyano-... 

Miscellaneous Fused Systems. - 3,4-Diaminothiophens have been shown to be excellent starting materials for thienot3,4-b]pyrazines and thienot3,4-b]-1,4-diazepines through the reaction with 1,2-dicarbonyl compounds and 1,3-diketones, respectively. Pyridinot2, 3 ... 

Miscellaneous Fused Systems.—The reaction of 2-vinylthiophen with azodicar-boxylates gave a mixture of tetra- and dihydro-thienopyridazine diesters upon dicarbethoxylation with TFA followed by oxidation, these gave thieno[2,3-c]pyridazine. ° Thieno[2,3-6]pyrazine has been synthesized from 2-chloro-3-cyanopyrazine by reaction with ethyl thioglycollate and condensation with base... 

Miscellaneous Fused Systems.— Ethyl 3-aminothieno[2,3- ]pyrazine-2-carboxyIate has been prepared from 2-chloro-3-cyanopyrazine and ethyl a-mercaptoacetate, and then converted into (269) by reaction with formamide. Other derivatives of (269) were subsequently prepared. Fused thieno[3,2-c/]-y/c-triazin-4-ones... 

Miscellaneous Fused Systems.— The oxidation of thieno[2,3-b]thiapyrylium perchlorate (490) with Mn02 gave, among other products, 2-thieno[2,3-b]-thiophenaldehyde and 2H-thieno[2,3-b]thiopyran-2-one/ Similar results were obtained with the isomeric thieno[3,2-b]thiopyrylium perchlorate. The l-benzothieno-[3,2-b]- and -[2,3-b]-selenopyrylium salts (491) and (492)... 

Benzoheteropine Rings with Two Heteroatoms on the Heteropine ring Systems with More than Two Atoms on the Heteropine Ring and Miscellaneous Ring Systems Reactivity of Benzoheteropines with Fused Five-Membered Rings... 

Section III deals with 1,2,5-thiadiazole 1,1-dioxides and fused systems. Other six-membered rings, such as thiatriazines and oxathiadiazines are gathered in Section IV, and Section V deals with miscellaneous compounds. Finally, in Section VI, the biological properties and other applications are described. 

The compounds of this series of fused (5 5 5) systems of three five-membered rings so far encountered may logically be divided into the following three distinct classes (1) linearly fused (5 5 5) systems, (2) angularly fused (5 5 5) systems, and (3) spiro-fused (5 5 5) systems. In addition to these three distinct classes, there are other compounds reported bearing bridged and propellane moities which are classified under the heading miscellaneous . 

The fused heterocyclic rings to be discussed here have normally been produced by an intramolecular cyclization of an N(6)-, N(2)- or S-substituent onto a ring nitrogen atom in the purine nucleus and are mainly five- or six-membered systems cyclonucleosides such as (210) are of course notable exceptions and a few miscellaneous examples exist. 

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