3-formyl-thiophene

Dimethyl-thiophen 3-Phenyl-thiophen 2-Formyl-thiophen 2-Benzoyl-thiophen... 

Schulte, K., u. N. Jantos Synthese von 2-PropinyI-5-formyl-thiophen... 

XXVI. The Synthesis of 5-(l-Propynyl)-2-formyl-thiophene, Junipal, and trans-Methyl-5-(l-propynyl)-2-thienylacrylate. Acta Chem. Scand. 13, 1460 (1959). 

Liebeskind and associates converted 3,4-diisopropyl squarate (97) to stannylcyclobutenedione 98 via a 1,4-addition-elimination sequence. 98 was then coupled with 2-iodothiophene to afford substituted cyclobutenedione 99 [85]. In another case, 3-lithioquinuclidin-2-ene, generated from the Shapiro reaction of 3-quinuclidinone (100), was quenched with Bu3SnCl to afford a unique enamine stannane 101. The Stille reaction of stannane 101 and 5-bromo-2-formyl-thiophene then furnished 3-thienylquinuclidine 102 [86]. 

Unter Katalyse mit Kupfer-Pulver ist sogar die Substitution des Brom-Atoms im relativ elek-tronenreichen 4-Brom-2-formyl-thiophen durch Imidazol zu l-(2-Formyl-4-thienyl -imidazol (74%) moglich775. 

Figure 4. GC-MS analyses. Top 2-methyl-3-furanthiol acetate (7), sample preparation I (SP I), GC column DB-1. Middle 2-formyl-thiophene (8), SPII, GC column DB-Wax. Bottom fiirfurylmethylsulfide (9), SPII, GC column DB-Wax.

For the first time the identication of 2-methyl-3-furanthiol acetate, furfuryl-methylsulfide, 2-formyl-thiophene and 4-methyl-5-vinyl-thiazol confirms the assumption that products from thiamine degradation and yeast lees are present in wines at trace level. 

The major advantage of the seunpling technique developed, was that some trace chemicals could be trapped tind described for the first time as Black Truffle aroma constituents. In particular, some compounds, important flavor contributors, generally appearing in small concentrations, such as benzaldehyde, propanal, ethyl acetate, anisole or dimethyl disulfide - previously identified in Shiitake mushrooms (9) - could be characterized. This was also the case for three aromatic compounds, toluene, xylene and ethyl benzene, well known as raw vegetable constituents (1 ). In addition, two aliphatic esters, isopropyl and sec-butyl formates, and one cyclic sulfur compound (2-formyl thiophene) previously reported respectively in plums and apples (W) and in coffee and bread products (n) were identified. 

Tab. 15 Formyl-thiophene aus Thiophenen mit Chlormethylen-dimethyl-iminium-dichlorphosphat... 

Various Physical Properties.—Radical cations of 2,5-dialkylthiothiophens have been obtained and their e.s.r. spectra interpreted in terms of unequally populated rotational isomers. The mass spectra of some simple thiophens and some azines derived from 2-acetyl- and 2-formyl-thiophens have been obtained. Molecular ion isomerizations occurring in 3-phenylthiophen and two brominated derivatives have been followed in both slow and fast reactions using C-labelling. Affinities, standard heats, and standard entropies of dyeing of some thiophen-containing azo dyes have been... 

Cantrell, T. S., Reactivity of photochemically excited 3-acylthiophenes, 3-acylfurans and the formyl-thiophenes and -furans, J. Org. Chem., 42, 3774, 1977. 

Acylation. To achieve acylation of thiophenes, acid anhydrides with phosphoric acid, iodine, or other catalysts have been widely used. Acid chlorides with AlCl, SnCl, ZnCl2, and BF also give 2-thienylketones. AH reactions give between 0.5 and 2.0% of the 3-isomer. There has been much striving to find catalyst systems that minimize the 3-isomer content attempting to meet to customer specifications. The standard procedure for formylation is via the Vil smeier-H a ack reaction, using phosphoms o xycbl o ri de / /V, / V- dim e tb yl fo rm a m i de (POCl /DMF) or /V-m ethyl form an i1 i de. 

The reactivity of five-membered rings with one heteroatom to electrophilic reagents has been quantitatively compared in a variety of substitution reactions. Table 2 shows the rates of substitution compared to thiophene for formylation by phosgene and iV,AT-dimethylfor-mamide, acetylation by acetic anhydride and tin(IV) chloride, and trifluoroacetylation with trifluoroacetic anhydride (71AHC(13)235). 

The effect of substituents on the reactivity of heterocyclic nuclei is broadly similar to that on benzene. Thus mem-directing groups such as methoxycarbonyl and nitro are deactivating. The effects of strongly activating groups such as amino and hydroxy are difficult to assess since simple amino compounds are unstable and hydroxy compounds exist in an alternative tautomeric form. Comparison of the rates of formylation and trifiuoroacetylation of the parent heterocycle and its 2-methyl derivative indicate the following order of sensitivity to substituent effects furan > tellurophene > selenophene = thiophene... 

The benzo[6] heterocycles are generally less reactive than their monocyclic counterparts. Thus benzo[6]thiophene unlike thiophene does not undergo Vilsmeier formylation or the Mannich reaction. 

A quantitative study has been made on the effect of a methyl group in the 2-position of five-membered heteroaromatic compounds on the reactivity of position 5 in the formylation and trifluoroacetylation reaction. The order of sensitivity to the activating effect of the substituent is furan > tellurophene >selenophene = thiophene (77AHC(2l)ll9). 

Thieno[3,4-h]thiophene, 2-methoxycarbonyl-formylation, 4, 1052 Thieno[3,4-c]thiophene, 1,3-dimethyl-synthesis, 4, 1058... 

Thiophene, 2-amino-3-cyano-5-phenyl-synthesis, 4, 888-889 Thiophene, 3-amino-4,5-dihydro-cycloaddition reactions, 4, 848 Thiophene, 2-amino-3-ethoxycarbonyl-ring opening, 4, 73 Thiophene, 2-amino-5-methyl-synthesis, 4, 73 Thiophene, 2-anilino-synthesis, 4, 923-924 Thiophene, aryl-synthesis, 4, 836, 914-916 Thiophene, 2-(arylamino)-3-nitro-synthesis, 4, 892 Thiophene, azido-nitrenes, 4, 818-820 reactions, 4, 818-820 thermal fragmentation, 4, 819-820 Thiophene, 3-azido-4-formyl-reactions... 

Thiophene, 3-pentadeuterophenyl-chemical shifts, 4, 730 Thiophene, 2-phenyl-oxidation, 4, 800 phototranspositions, 4, 743 rearrangement, 4, 42 reduction, 4, 775 synthesis, 4, 865, 914 UV spectrum, 4, 735 Thiophene, 3-phenyl-photochemical rearrangements, 4, 735 phototranspositions, 4, 743 lsmeier formylation, 4, 759 Thiophene, 2-pivaloyl-Birch reduction, 4, 775 Thiophene, polybromo-reactivity, 4, 829 Thiophene, polylithio-synthesis, 4, 831 Thiophene, (propargylthio)-rearrangement, 4, 746 Thiophene, 2-(3-pyridinyl)-synthesis, 4, 781 Thiophene, 2-(5-pyrimidinyl)-synthesis, 4, 781 Thiophene, 3-pyrrolidinyl-cycloaddition reactions, 4, 68 with dimethyl acetylenedicarboxylate, 4, 788-789... 

The introduction of the cheap and commercially available N,N-dimethylformamide, instead of A-methylformanilide in the POCI3 catalyzed Vilsmeier formylation of thiophene, has made 2-thio-... 

It is thus apparent that the selectivity of a reagent toward thiophene and benzene can differ appreciably, and this difference in selectivity is also strongly noticeable in the proportions of 2- and 3-isomers formed. Although in certain reactions no 3-isomer has been detected, appreciable amounts have been found in other reactions. Thus 0.3% of the 3-isomer has been found in the chlorination of thiophene.- Earlier results indicated that 5-10% 3-nitrothiophene is formed in the nitration of thiophene and a recent gas-chromatographic analysis by Ostman shows that the mononitrothiophene fraction contains as much as 16% of the 3-isomer. It appears that gas-chromatographic analysis should be very useful for the detection of small amounts of 3-isomers in other substitution reactions. However, from routine analyses of IR spectra, it appears to the present author that the amount of 3-isomers formed in acylation, formylation, and bromina-tion of thiophene are certainly less than a few per cent. 

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