2-Thenyl halides

Relatively straightforward benzene analogue reactivity is found with thenyl halides, alcohols (conveniently preparable by reducing aldehydes) and amines, from, for example, reduction of oximes. One exception is that 2-thenyl Grignard reagents usually react to give 3-substituted derivatives, presumably via a non-aromatic intermediate. ... 

In the second class of synthesis two thiophene rings become joined through a carbon atom that is already a substituent of one of them by this means symmetrically and unsymmetrically substituted products in the 2,2, 2,3, and 3,3 series are available. Three main reaction types have been employed in this approach. In one of these a thiophene is alkylated with a thenyl halide (Eq. 3). Friedel-Crafts acylation of a thiophene by a thenoyl chloride or thenoic acid followed by reduction of the resulting dithienyl ketone provides a second route in this category. The last and most versatile synthesis in this class involves reaction of a thienyllithium (or Grignard reagent) with a thienylaldehyde or thienyl ketone reduction of the carbinol (see Eq. 2) then gives the dithienylalkane. 

Relatively straightforward benzene-analogue reactivity is found with thenyl halides, alcohols (conveniently preparable by reducing aldehydes) and amines,... 

The thenyl cyanides are of great importance for the preparation of thiophene derivatives. Because of the acidifying effects of both the thienyl and of the cyano groups, carbanions are easily obtained through the reaction with sodamide or sodium ethoxide, which can be alkylated with halides, carbethoxylated with ethyl carbonate, or acylated by Claisen condensation with ethyl... 

Reactive halogen compounds such as benzyl chloride, 2-thenyl chloride, 2-bromoacetylthiophene, (C HjS)COCH,Br , and 2-chloromethyl-thianaphthene (C,H5S)CHjCl are readily converted to esters by treatment with the sodium salts of carboxylic acids. A small amount of tri-ethylamine has proved to be an effective catalyst. Acetates are oftentimes made by heating halides with fused sodium acetate in glacial acetic acid, e.g., p-ethylbenzyl acetate (93%). The reaction is of little value for the preparation of simple aliphatic esters. Secondary and tertiary halides give increasing amounts of olefin by dehydro-halogenation. 

---