Fused Selenophens

Miscellaneous Fused Selenophens.—Selenolo[2,3-6]thiophen (691) has been prepared by metalation of thiophen 3-aldehyde diethyl acetal with butyl-lithium followed by reaction with selenium and methyl chloroacetoacetate. The intermediate (692) was, without isolation, hydrolysed and ring-closed to (693), which upon decarboxylation gave (691). Another isomeric 

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Selenolo[3,4- ]furan 97 was prepared utilizing the organic selenium transfer reagent iV,A -diethylselenopropion-amide 96 (Equation 13) <1998JHC71>. Treatment of bromoketone 95 with 96 gave the [[Pg.991]

An inorganic selenium electrophile, selenium oxychloride (SeOCl2), has been utilized to prepare fused selenophenes <2002JOC2453>. Deprotonation of bis(cyanide) 104 with LDA followed by treatment with selenium oxychloride gave the benzo[c]selenophene 105 (Equation 15). This sequence also allowed for the preparation of a thieno[3,4-f]selenophene. 

A convenient one-step synthesis of fused selenophenes has been developed <1994H(38)143, 1996T471>. For example, heating ynediol 106 in the presence of selenium metal gave selenolo[3,2- ]selenophene 107 (Equation 16). 

An approach amenable to the preparation of various fused selenophenes and benzo[3]selenophenes involves the treatment of 1,4-dilithiated intermediates with bis(phenylsulfonyl)selenide 112 <1994CPB1437>. The synthetic sequence to the selenolo[2,3-/ ]selenophene 113 from 3-ethynylselenophene 110 is shown in Scheme 11 <1997H(45)1891>. A stereoselective hydroalumination of 110 with diisobutylaluminium hydride (DIBAL-H) followed by bromination with NBS gave dibromo compound 111. Dilithiation of 111 followed by treatment with selenium electrophile 112 gave 113. 

Additional examples of selenophene ring-formation reaction that result from the treatment of 1,4-dienes with selenium dioxide have been reported. For example, treatment of verbenone derivative 116 with selenium dioxide in the presence of pyridine gave fused selenophene 117 in 92% yield (Equation 19) <20010L3161, 2002JOC6553>. Additional applications of this reaction include taxol analog 150 <1997BML1941> and a [l]benzopyrano[3,2-/ ]-selenophene-9-one derivative <2001SAA1427>. 

Substituent effects in 2-substituted selenolo[3,2-Z>]selenophens have been studied by H, and Se n.m.r. spectroscopy good linear correlations between these shifts and those of thieno[3,2- >]thiophens were observed. The H, and Se n.m.r spectra of some selenolo[3,2-c] thiophens have also been studied. CNDO/2 calculations have been carried out on selenophen and on [2,3-b] [3,2-Z>] and [3,4-b] -fused selenophens. ... 

A modest number of reports detailing the synthesis of selenophene derivatives have appeared. Treatment of cinnamaldehyde (256) with selenide 257 gave dihydroselenophene 258 . A formal [3+2] cycloaddition of selenide 259 with DMAD gave dihydroselenophene 260 . Novel tetrathiafulvene-fused selenophenes and... 

Benzoselenophene [111, 112] and related fused selenophenes [113-116] were previously obtained via tedious multistep reactions involving a selenocyclization reaction from barely accessible selenium-containing compounds. Such conventional synthetic methods are unsuitable for the development of selenophene-based OFET materials. Sashida s group developed a simple one-pot preparation of benzoselenophenes by an intramolecular selenocyclization reaction of acetylene compounds with a selenolate anion [117, 118]. This allowed straightforward access to sophisticated fused selenophenes, such as 52 and 53, from commercially available chemicals [119, 120]. Scheme 6.9 depicts the key selenocyclization reaction used in the synthesis of 52. This synthetic protocol was also successfully applied to the synthesis of regioisomer 54 [121]. 

Decarboxylation of the acids gave the parent compounds (541) and (542). The product of condensation between o-(methylseleno)phenylacetic acid and o-methylthio- or o-methylseleno-benzaldehydes (549) gave the tetracyclic derivatives (550). These were also obtained by Rieche formylation of (551). The pyrrole-fused selenophen (552) was prepared similarly to the... 

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