Substitution Reactions in the Selenophene Series

Selenophene undergoes various electrophilic substitutions nitration, sulfonation, halogenation, mercuration, chloromethylation, aminomethylation, acylaminomethylation, acylation, formylation, and hydrogen exchange. 

Nitration with fuming nitric acid in acetic anhydride occurs mainly at the a. position, to give 85% 2-nitroselenophene and 15% 3-nitro- 

Shatenshtein, Isotope Analysis of Water. USSR Acad. Sci., Moscow, 1957 (in Russian). 

2 -Diselenienyl, obtained by Chierici et oZ.46 from the reaction of 2-iodoselenophene with activated copper, is nitrated to form the 5,5 -dinitro derivative. 

selenophenes are nitrated preferentially at the 2-position unless this position is occupied by an electron-accepting group (N02, CHO, COCH3, or S02C1) then nitration occurs mainly in the 4-position. The free a position (5-position) is substituted only to about 10-15%. 

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Nucleophilic substitution reactions in the selenophene series have attracted some interest. Debromination of bromonitro compounds [(50, X = S, Se) and (53, X = S, Se)] with sodium thiophenoxide and sodium selenophen-oxide72 was studied. Selenophene compounds were four times more reactive than the thiophene derivatives. The position of attack, a or /), had very little influence on the rate ratio. The kinetics of the side-chain nucleophilic reactions of selenophene derivatives, shown in Scheme 4, has been reported.7 3... 

N. K. Sadovaya, Substitution Reactions in the Selenophen Series, Candidate s Dissertation, Moscow University (1962). 

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