engleski

Preparation of Ferrocenylthialiphatic Acids and Their Reactions with Trifluoroacetic Anhydride

The extraordinary ability of ferrocene nucleus to stabilize the carbocations in position adjacent to cyclopentadienyl ring is known, but the influence of ferrocene to cations in b-position is not well-documented. The objective of this work was to examine the possibilities of formation and fate of alpha- and ß-ferrocenyl carbonium ions by the action of trifluoroacetic anhydride (TFAA) on the corresponding ferrocenylthiaaliphatic acids, Fc(CH2)mCHRS(CH2)n COOH (3). The acids 3 were prepared in TFA-catalyzed reactions of the corresponding carbinols 1 with the appropriate mercaptoaliphatic acids in 75-99 % yields (m = 0),(S. Lisac, V. Rapic, J. Organometal. Chem. 507 (1996) 215) and in 18-25 % yields (m = 1). Reactions of bromides 2 with the same mercaptoaliphatic acids in NaOH/EtOH gave 81-84 % of 3 (m = 1) and 72-76 % of 3 (m = 2). The obtained thiaacids were characterized as esters 4 and hydrazides 5. The action of TFAA on acids 3 (m = 0) gave 1,2-disubstituted 1,2-diferrocenylethanes and the corresponding oligomers which must have been formed via the intermediate a-ferrocenyl carbocations . In contrast, we found that thiaacids 3 (m = 1) gave in the same circumstances the intramolecularly cyclized products , as well as S-benzylthioglycolic acids.These results indicated that the appropriate ß-ferrocenyl carbonium ions were not formed under the reaction conditions.

ferrocenylthialiphatic acids

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