Heteroarene fused

The introduction of sulfur between two ortho amino groups is the oldest and still the most commonly used route to benzo- and heteroarene-fused 1,2,5-thiadiazoles. The reaction has been extensively reviewed in both CHECK 1984) and CHEG-II(1996). The in situ preparation of Ar-sulfinylanilinc via /3-elimination of chloroform from trichlorometh-anesulfinamides 200 was recently supported by trapping with 1,2-benzenediamine to give the benzothiadiazole 2 in 85% yield (Equation 43) <1997TL487>. 

A useful strategy for the formation of fused thiadiazoles is the annulation of suitably functionalized 1,2,5-thiadiazoles. Common routes involve the use of 3,4-difluoro-l,2,5-thiadiazole, 3,4-diamino-1,2,5-thiadiazole, l,2,5-thiadiazole-3,4-dicarbonyls, l,2,5-thiadiazole-3,4-dicarbonitrile, amino-1,2,5-thiadiazole-3-carboxamides and carboxamidines. These afford heteroarene-fused 1,2,5-thiadiazoles (which are covered in Volume 9). Below follows a brief description of fused thiadiazoles that fall within the scope of this chapter. 

B.iv.b. Regioselective Synthesis of Benzene Derivatives via Pd-Catalyzed Cross-Coupling of 4-Halo-2-cyclobuten-l-ones. The Pd-catalyzed reaction of 4-chloro-2-cyclobuten-l-ones with alkenylzirconium derivatives or alkenyltins and heteroaryltins followed by thermolysis at 100 °C has regioselectively (—95%) produced multiply substituted benzenet" (Scheme 17) and heteroarene-fused benzene derivatives (Scheme 18), respectively. 

Heteroarene-fused barrelenes are generally synthesized from a-diketones 7 and 1,2-diamines. Pyrazinobarrelenes"" could be prepared either by condensation of a-diketones 7 with ethylenediamine followed by oxidative generation of the pyrazine ring or by direct condensation of 7 with diaminomale-onitrile (Scheme 2). Quinoxalinobarrelenes, " benzo(g]quinoxalinobarrelenes, " and dibenzo(//ij-quinoxalinobarrelenes are easily obtained by simple condensation of 7 with o-phenylenediamines, 2,3-diaminonaphthalene, and 9,10-diaminophenanthrene, respectively. 

Within the barrelene system, the photochemistry of dibenzobarrelene and its derivatives have been extensively investigated, presumably due to their easy accessibihty as well as the interesting mechanistic aspects. This material is covered in depth in other articles - and discussed here to the extent required for comparison with photochemical studies of heteroarene-fused barrelenes. Ciganek reported that the acetone-sensitized reaction of dibenzobarrelene 32 results in the formation of dibenzosemibuUvalene 34. 

As a further extension of the photochemistry of heteroarene-fused barrelenes, dibenzo(/,/i]-quinoxali-nobarrelenes have been subjected to photoisomerization in this laboratory. Upon direct irradiation of 101 in cyclohexane, the DPM product 102 and the ADPM products 103 and 104 are obtained. The vinyl-vinyl bridged product 102 is minor (Scheme 12). Similarly, the reaction of heterobarrelene 105 under direct irradiation proceeds through both the DPM and the ADPM modes and produces SBs 106-108. Again, the DPM product 106 is formed as a minor photoproduct (Scheme 13). ... 

Benz-fused analogues are also covered in this chapter. The possible benz-fused parent systems are 2,1-benzothiaze-pine 4, 1,2-benzoxazepine 5, 3,2-benzoxazepine 6, 2,3-benzoxazepine 7, 2,1-benzothiazepine 8, 1,2-benzothiazepine 9, 3,2-benzothiazepine 10, and 2,3-benzothiazepine 11 derivatives of some of these systems are included. A major reference series has reviewed seven-membered heteroarenes with two or more heteroatoms <1997HOU(E9d)299>, while the syntheses of benzoxazepines, including 2,3-, 3,2-, and 2,1-skeletons, have also been reviewed <1997MI1>. 

Fused aromatics. Symmetrical and unsymmetrical zirconacydopentadienes are readily prepared from CpjZrBuj and alkynes or diynes. A CuCl-mediated reaction of these metallocycles with 1,2-dihaloarenes and heteroarenes gives fused aromatic products. The... 

Tetrathiabenzo[l,3-cfirst time by dimerization of thieno[2,3- >]thiophene (142) (92PS73). More recently, it was found that catalytic reduction of 3,4-dibromothieno[2,3-i]thiophene (227) with an excess of activated zinc in the presence of bis(triphenyl-phosphine)nickel(II) chloride and tetraethylammonium iodide afforded only 4,4 -dibromo-3,3-bis(thieno[2,3- )]thiophene) (228) (in a maximum yield of 28%) (89AG1254). However, the reaction in the presence of a larger amount of the nickel catalyst afforded also dipenatlene 225. Optimization of the reaction conditions made it possible to increase the yield of the latter to only 14%. An alternative procedure was employed to transform thienothiophene 227 into trimethylstannyl derivative 229. The reaction of thienothiophene 227 with organotin intermediate 229 in the presence of the palladium triphenylphosphine complex afforded dipentalene 225 (13% yield). Derivatives 226 were prepared by lithiation of... 

Fused indole 232 resulted from the reaction of a donor-acceptor cyclopropane with an indole bearing a Michael acceptor at C2.The products were obtained in good yield with high diastereoselectivity (16 examples, 64-90% yield) (140L3954). Tetracyclic-fused indole 233 was prepared by a [3+3]-cycloaddition of an indol-2-yl carbinol with an azadiene (11 examples, 42-90% yield). This could be followed by an oxidative ring expansion promoted by (bis(trifluoroacetoxy)iodo)benzene to produce a series of indole azepinones (6 examples, 59-71% yield) (14CC11181). Fused indole 234 was synthesized by the first calcium(II)-promoted Nazarov cyclization (87% yield).The substituent a to the ester functionality could vary electron-rich arenes, heteroarenes, and secondary alkyl... 

SFs-Substituted fused aromatic heterocycles derived from various SFs-arenes and having an SFs-group attached to the benzene part of a ben-zannulated molecule represent the largest group of SFs-heteroarenes known to date. Wide commercial availability of various SFs-substituted benzenes and the possibihty of their further transformation into more complex... 

Several approaches have been followed for the generation of optically active heteroarenes by homogeneous asymmetric hydrogenation. One approach involves direct asymmetric hydrogenation of the unactivated heteroarene. This approach has been most successful for heteroarenes that are polycyclic, like quinolines, isoquinolines, or quinoxa-lines (benzopyrazines). Less success has been achieved on the direct asymmetric hydrogenation of pyridines. To address this limitation, the hydrogenation of modified pyridines has been conducted. In one set of examples, pyridines and related benzo-fused heteroarenes were modified at tfie nitrogen by acylation or the installation of another auxiliary to make the pyridine more electron poor and to dock the catalyst. In a second set of examples, a chiral auxiliary was placed on the pyridine, and the product was formed diastereoselectively by an achiral catalyst. 

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