Thiophenes, acetyl nucleophilic substitution

This order of reactivity was observ for add dedeuteration, but for acetylation, formylation, and chlorination it was slightly different thieno[3,2-h]thiophene (2) > thieno[2,3-h]thiophene (1) > thiophene thieno[3,4-6]thiophene (3) was not studied. A substantially greater discrepancy between theoretical and experimental data was observed for nucleophilic substitution from the data on base dedeuteration and competitive metalation reactions/ the order of decreasing reactivity was as follows thieno[2,3-h]thiophene (1) > thieno[3,2-h]thiophene (2) > thiophene. To a certain extent this may be explained by differences in the mechanism of metalation and deuterium exchange with a base. A discrepancy between calculation and experiment was also found for free-radical substitution. ... 

Nice examples of nucleophilic substitution on a thiophene ring are represented by nucleophilic substitutions of 5-acetyl-2-chloro-3-nitrothiophene (Scheme 103) [164], The acetyl group, as a second electron-withdrawing group, in addition to the nitro group, was necessary to support successful nucleophilic substitution. Various nucleophiles were effective, including aliphatic and aromatic V-nucleophiles, aliphatic 0-nucleophiles as well as aliphatic S-nucleophiles (Scheme 103) [164],... 

Benzaldehyde dioxolan is cleaved by butyl lithium to e butyrophenone, ethylene, and butane as products [5] a similar reaction occurs with phenyl lithium [5a]. On the other hand the dioxolans of 3-thiophene aldehyde [219] and of 2-acetyl thiophene [220] are metalated normally in the nucleus by the same reagent, and substitution products are obtained in good yield (Fig. 9.10). Clearly, competition for the nucleophilic reagent is the factor accounting for these differences. 

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