Thiophene, 2,3-dehydro

Dehydrobenzene or benzyne 158 can be trapped by all manner of species. 1,2-Dehydro-o-carborane 159 has been shown to undergo many of the same reactions as its two-dimensional relative, 1,2-dehydrobenzene. Although dehydroaromatic molecules can be formed in a variety of ways, synthetic pathways to 1,2-dehydro-o-carborane are quite limited. An effective procedure reported so far78 first forms the dianion by deprotonation of o-carborane with 2 equiv. of butyllithium. Precipitated dilithium carborane is then treated with 1 equiv. of bromine at 0°C to form the soluble bromo anion 160. Thermolysis of 160 with anthracene, furan, and thiophene as substrates leads to the adducts 161-164.79 80 1,2-Dehydro-o-carborane reacts with norbomadiene to give both homo 2+4 and 2+2 addition, leading to three products 165-167, in a 7 1 ratio79. An acyclic diene, 2,3-dimethyl-... 

Reaction of various aldehydes with hydrogen sulfide leads to substituted thiophenes, dihydrothiophenes, dithiolanes and trithiolane, as well as to six-membered ring thiopyran derivatives and dithiins. Ledl (33) obtained 2,4-dimethylthiophene (1, R Me) as a product of the reaction of propionaldehyde with hydrogen sulfide in the presence of ammonia. Sultan (29) reported the formation of 2,4-diethylthiophene (1, R - Et), 2,4-dibutyl-thiophene (1, R - Bu), and their dehydro derivatives from the reaction of ammonium sulfide with butyraldehyde and caproaldehyde (hexanal), respectively. The mechanism suggested for their formation is depicted in Scheme 1. Space limitations do not allow us to discuss the mechanism here in detail (for additional information, see ref. 29). 

The stability of the o-bromothienyllithium reagents at — 70°C contrasts sharply with the behavior of o-bromophenyllithium which is very unstable even at —lOO C, readily splitting off lithium bromide to form benzyne (dehydrobenzene) Only by heating bis-(3-iodo-2-thienyl) mercury to 240°C in the presence of tetracyclone could some evidence for the intermediate existence of 2,3-dehydro-thiophene be obtained. ... 

Route 1 involves an initial migratory arylzincation pathtvay that is followed by a copper-mediated reaction with elemental sulfur, with accompanying C-S cyclization to afford a substituted benzothiophene in a one-pot reaction. Alternatively, in route 2, the zinc intermediate is first trapped by iodine, and subsequent copper-catalyst allows C-S/C-Se bond formation followed by cyclization in the presence of elemental sulfur or selenium to afford the corresponding benzochalcogenophene. A modular two-step synthesis of dithieno[3,2-l) 2, 3 -d]thiophene derivatives by C-S cross-coupling and oxidative dehydro C-H coupHng was also described in the year 2014 (14OL4086). 

The highly twisted Ti-conjugated macrocycle (184) with two allq nyl moieties underwent intramolecular [2 + 2] photocycloaddition to give the thiophene-fused bisdehydro[12]annulene (185) in 61% yield. Photolysis of the bis(dithienyl)ethynes (186) in the presence of iodine resulted in sequential electrophilic and photochemical cyclizations to yield the tetrathienonaphthalenes (183) in one pot reactions. The compounds (187) showed a significant potential as a cruciform scaffold for nanostructured Ji-electron materials. The alkenyl-substituted bis(dithienyl)ethynes (188) underwent p-benzoquinone photosensitized double 5-exo-cyclization to give the diarylated dithienofulvalenes (189). The atylpyridinylethynes (190) and (191) in aqueous HCl solution underwent photo-dehydro-Diels-Alder reaction to afford... 

Some aminobenzoic acid diuretics containing the thiophen ring have also been studied. The syntheses and lipid-lowering properties of (203) and (204) have been described. 3-j8-(2-Thienyl-alanine-8-lysine)vasopressine has been synthesized by the solution technique. A comparison of the bioavailability of [2,5- C]thiophen after oral and rectal administration in mice has been reported. The nitro-reduction of carcinogenic 5-nitro-thiophens by rat-tissues has been studied. Thiophen-ring-containing compounds with antiradiation, antidepressant, antiparasitic, " antibacterial, - antiviral, and broncho-dilator activity have been studied. A thia-steroid, 14,15-dehydro-A-nor-3-thiaequilenin, has been synthesized. In connection with studies on the syn-... 

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