Thiophenes, acetyl mercuration

H NMR, 4, 1042 ionization potentials, 4, 1046 synthesis, 4, 1066 UV spectra, 4, 1044 Selenolo[2,3 -cjthiophenes H NMR, 4, 1042 synthesis, 4, 1067 UV spectra, 4, 1044 Selenolo[3,2-6]thiophenes dipole moments, 4, 1049 H NMR, 4, 1042 ionization potentials, 4, 1046 synthesis, 4, 1066 UV spectra, 4, 1044 Selenolo[3,4-6]thiophenes synthesis, 4, 1067 Selenolo[3,4-c]thiophenes addition reactions, 4, 1062 synthesis, 4, 1076 Selenomethionine applications, 4, 970 Selenophene, 3-acetamido-reactions, 4, 953 Selenophene, 2-acetyl-mercuration, 4, 946 nitration, 4, 947 Selenophene, 2-alkyl-reactions, 4, 45 synthesis, 4, 135, 967 Selenophene, 3-alkyl-synthesis, 4, 135, 967 Selenophene, 3-aryl-synthesis, 4, 963 Selenophene, 2-benzyl-reactivity, 4, 946 Selenophene, 2-benzyl-5-ethyl-reduction, 4, 950... 

The mercuration of 2-substituted thiophenes by mercuric acetate at temperatures between 16.9 and 50.0 °C has been shown to be second-order over the first 20 % of reaction449. The activation energies for thiophen and its 2-acetyl, 2-methyl,... 

Thiophenes, acetyl-, 239, 241 dinitro- reactions of, 350 2-halogono-, reactivity of, 351 halogeno-nitro-, 293, 347, 348 mercuration of, 239 nitro-, polarograi c reduction of, 239, 241... 

Propionylation (EtCOCl/SnCl4/CS2) of thienothiophene 2 readily gives (in 88% yield) 2-propionylthieno[3,2-i]thiophene. With acetic anhydride and traces of iodine, 2 yields 2-acetylthieno[3,2-6]thiophene (50%). The latter was also prepared by acetyl chloride treatment of the monomercury compound produced by mercuration (HgClj) of thienothiophene 2. ... 

Tetrahydrobenzo[ ]thiophene behaves like thiophene in electrophilic substitution reactions. Thus, it is formylated with a mixture of vV-methylformanilide and phosphorus oxychloride,436 iodinated in the presence of mercuric oxide,193 and brominated by V-bromosuccinimide,193 all in the 2-position in Friedel-Crafts reactions with acetyl chloride,194-436 propionyl chloride,436 succinic... 

Challenger and co-workers18,19,21,22 first used mercuration (HgClj) to isolate and purify the thienothiophenes from the reaction of acetylene with sulfur. Thieno[3,2-fc]thiophene gave a mixture of mercury derivatives with mercuric chloride both in the presence and in the absence of sodium acetate. The 2-monochloromercury derivative was isolated and converted to the corresponding acylthieno[3,2-h]thiophene with acetyl or propionyl chloride.21,218 The reaction of thienothiophene 2 with mercuric acetate affords the 2-acetoxymercury derivative.20... 

Rate constants for the mercuration of selenophene and its 2-bromo, 2-carboethoxy, 2-acetyl, and 2-nitro derivatives under the conditions employed by Motoyama et al.,121 have been determined at various temperatures by Yur ev and his co-workers.304 The selenophene derivatives were mercurated from 1.5 to 3 times more rapidly than the corresponding thiophene derivatives. A straight line is obtained in the Hammett plot with ap+ constants, with a p value of — 5.7 at 25°. 

A second quantitative comparison of the reactivity of selenophene with that of thiophene is by the kinetics of mercuration (at the 5-position) of 2-substituted derivatives of the two series. It was found that 2-bromo-, 2-acetyl-, 2-carbethoxy-, and 2-nitroselenophenes59 are mercurated 1.5 to 3 times faster than the corresponding derivatives of thiophene.89 The substituent effects for selenophenes follow the Hammett equation using a+ values. 

Isomer distributions have been determined for several electrophilic substitutions of thiophen, such as bromination by Bra and Br+, chlorination by tin tetrachloride, or iodine-catalysed acetylation by acetic anhydride, trifluoroacetylation, and Vilsmeyer formylation. The a. ratios vary from 100 to over 1000, according to the selectivity of the electrophilic agent. The results obtained, together with other data from the literature, permit a test of the applicability of linear free-energy treatments to electrophilic substitution at the a- and j8-positions of thiophen. Plots of log (Xf and log jSf against p for nine reactions were linear, and from the slopes values of = — 0.79 and 0)3+ = — 0.52 were obtained. Serious deviations were observed for mercuration and protodemercuration, while nitration and protodeboronation were not taken into account, as deviation could be expected for various reasons. The linearity was taken as evidence... 

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