Thieno-, Furo-, and Pyrrolo-thiophens

Thieno-, Furo-, and Pyrrolo-thiophens. - Partial rate factors for the detritiation of thieno[2,3-Z ] thiophen and thieno[3,2thiophen that were specifically labelled with tritium in each position have been measured, along with that for thiophen in either pure trifluoroacetic acid or a mixture of acetic acid and trifluoroacetic acid. Annelation of thiophen by thiophen produced a comparable change in reactivities of the a- and j8-positions, in contrast to annelation by benzene, where the reactivity of the 3-position is markedly increased relative to that of the a-position.  

Zherdeva, A. Ya. Zheltov, and B. I. Stepanov, Izv. Vyssh. Uchebn. Zaved., Khim. Khim. Tekhnol., 1981, 24, 246. 

The Fischer indole synthesis has been very difficult to carry out in the thiophen series. However, the reaction of (271) with cyclohexanone gave (272) in good yield. Attempts to apply the Fischer reaction to (273), which was prepared from (147), led to (274). Compound (275), of interest as a j3-blocker, was instead obtained starting from 212 )P Heating 2- and 3-(co-azido)vinylthiophen, prepared via bromoacetylthiophen and azidoacetyl-thiophen, followed by reduction and dehydration, gave thieno[2,3-i)]- and thieno[3,2-Z ]-pyrrole. Thermolysis of (276) gave diethyl thieno[3,2-b]-pyrrole-5,6-dicarboxylate in 76% yield.  

The reaction of (277) with methyl chloroacetate followed by ring-closure gave (278), which could be hydrolysed and decarboxylated to the parent compound. A review on [3 + 1]- and [4 + 1 ]-cycloadditions of isocyanides to dipoles and to nitroalkenes mentions work from a French 

9-Aza-azuleno[2,l-b] thiophen has been prepared from 2-chloro-3-formyl-l-aza-azulene by annelating the thiophen ring by the Fiesselmann reaction.  

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