Thiophene product

Based on these observations, it is likely that the mechanism involves initial formation of thione 3 (X = O or S), which is followed by tautomerization to 4 and cyclization to 5. Aromaticity drives the facile elimination of either H2O or H2S resulting in the thiophene product. 

Tetrahydrothieno[3,2-( ]pyridine undergoes an unusual reaction with ethyl propiolate to afford compound 62 instead of the expected ring opening to give a thiophene product (Equation 9) <2004CHE519>. 

As shown in Fig. 7.12, various aldehydes, ketones and acylating agents have been employed to generate the desired thiophene products in high yields (81-99%) and in generally good purities (70-99% as determined by HPLC). The resulting products could be purified by preparative HPLC if necessary to allow structural confirmation analysis. 

Photolysis of [czs-Fe(H)2(dmpe)2] with simple thiophenes at 273 K gives C-H and C-S insertion products. Prolonged photolysis (15 h) of the thiophene product mixture at 273 K does not appear to affect the relative ratios of the C-H and C-S adducts suggesting that they are stable under the photochemical conditions of the experiment. 

The yield of hydrogen was always smaller than that of the thiophene, and in fact the major portion of the thiophene product arises from the secondary photolysis of vinylthiacyclopropane, a primary product. That the photolysis of vinylthiacyclopropane affords thiophene was demonstrated in separate experiments. A possible mechanism is as follows ... 

A selected intramolecular Diels-Alder reaction of an acetylenic thiazole provided the expected thiophene product [Eq. (10)].59g... 

The mechanism leading to thiophene formation is presumed to involve dissociation of one sulfur atom of a dithiolene ehelate followed by sulfur attack on a pyrazine carbon, cyclization and oxidation to form a thiophene ring (A in Scheme 2.21). When the dithiolene-forming reaction in Scheme 2.20 employed a pterinyl alkyne, no tris-pterinyldithiolene complex could be isolated. However, pterinyl dithiolene formation was implied by the isolation of a pterin thiophene whose identity was eonfirmed by X-ray crystallographic determination (B in Scheme 2.21). This observation was an early confirmation of the correctness of the proposed pterin-dithiolene in Moco prior to any available X-ray protein structures. These thiophene products were reminiscent of Moco oxidation products 1 and the natural metabolite of Moeo, urothione 2 (see Figure 2.2), studied by Rajagopalan (C in Seheme 2.21). 

An interesting example of the Fiesselman thiophene synthesis was reported during the investigation of the susceptibility of golfomycin A toward nucleophilic attack. Treatment of TBS-protected golfomycin A with methyl thioglycolate in the presence of base produced the strained thiophene product in 20% yield. ... 

The Gewald aminothiophene synthesis was employed in the generation of 2-amino-3-(3,4,5-trimethoxybenzoyl)-5-aryl thiophenes as derivatives of the anti-tubulin agent combretastatin A." Condensation of 2,5-dihydroxy-1,4-dithiane with 3-oxo-3-(3,4,5-trimethoxyphenyl)-propionitrile and elemental sulfur in the presence of triethylamine afforded the thiophene product in 74% yield. Further synthetic steps yielded an antitubulin agent that not only inhibited tubulin polymerization but also showed anti-proliferation activity against both L1210 and K562 cancer cell lines. 

Figure 4.2 Bromination of thiophene product distribution at 50°C. Taken from [26].

Buitelaar RM, Cesario MT, Tramper J (1992) Elicitation of thiophene production by hairy roots of Tagetes patula. Enzyme Microb Technol 14 2-7... 

In an alternative use of thioamides, the ring-closing step involves the formation of the 4,5-bond of thiophene product (Scheme 70) [113]. 

If two equivalents of the 2-halo-carbonyl compound (or 2-halo-nitrile) are utilised to react with an enolate/carbon disulfide adduct, double S-alkylation and then double ring closure produce thieno[2,3-h]thiophenes [129] Scheme 82 shows how this works. Taking this idea further, if a malonate is used as the 1,3-dicarbonyl component, 3,4-dihydroxythieno[2,3-h]thiophenes are the final result (Scheme 83) [130], the ring closure steps then having the character of Claisen condensations. If malononitrile is used instead of a 1,3-dicarbonyl compound, the product is a 3,4-diaminothieno[2,3-6]thiophene - product 60 in Scheme 84 is the result of using chloroacetonitrile in the alkylation step [131]. 

Thiophene Product Ratio (thiophene silane acid) Time Yield (%)... 

Ketel, D.H., and H. Breteler Morphogenesis and Thiophene Production in Cell Cultures of Tagetes species. Bioact. Mol. (Chem. Biol. Nat.-Occurring Acetylenes Relat. Compd.) 7, 267 (1988). 

Thiophene Production by Crown Gall and Callus Tissue of Tagetes patula. 

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