2-Thienyllithium, reaction with

By reaction of 3-thienyllithium with magnesium bromide, the Grignard reagent, free from entrainment Grignard reagent, was obtained,- which is useful for the preparation of 3-acetothiophene by reaction with acetic anhydride at —70 0 and for the preparation of 3-t-butoxythiophene through reaction with t-butyl perbenzoate. It is the opinion of the present author that most 3-substituted thiophenes are prepared more conveniently from 3-thienyllithium than from 3-thenyl bromide. The latter method, however, is superior if the introduction of the 3-thenyl group is desired. 

Thienyllithium has been used for the preparation of triphenyl-2-thienylsilane, 2-thienylsulfinic acid, and di-2-thienylketone by means of reactions with triphenyl chlorosilane, sulfur dioxide, and... 

Thiophenethiols are prepared by reduction of the sulfonyl chlorides or, more conveniently, by the reaction of Grignard rea-gents or thienyllithium compounds with sulfur. They have also been obtained by cleavage or thienyl alkyl sulfides with sodium in liquid ammonia. 3-Thiophenethiol is a by-product in the commercial thiophene synthesis. Thiophenethiols have recently also been prepared by a synthesis involving Friedel-Crafts reaction of 2,4-dinitrobenzenesulfenyl chloride with thiophenes, followed by basic cleavage of the resulting sulfide. ... 

Thienyllithium derivatives undergo a variety of useful reactions with various electrophiles those of 2-thienyllithium have been reviewed (790R(26)1>. The following examples illustrate the type of new bonds that can be formed. 

Alkylation of thienyllithium with 5-alkyl halide may lead to a competitive elimination reaction. This has now been overcome the reaction with trialkylboranes, followed by treatment with iodine, gives the corresponding alkyl derivatives in good yields (Scheme 172) (79BCJ1865, 81BCJ1587). 

Another electrophilic reagent which has been used to introduce an oxygen function is alkyl peroxybenzoate. Thus 5-methoxy-2-thienyllithium on reaction with r-butyl peroxy-benzoate gives 2-r-butoxy-5 -methoxythiophene in 72% yield (790R(26)1>. 

A general reaction with wide applicability is the ring opening undergone by 3-thienyllithium derivatives. This is classified as an endo fission (78CRV517). The process is shown in Scheme 178. 

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