Reactions Leading to Destruction of the Thiophen Ring

Reactions Leading to Destruction of the Thiophen Ring.—Raney-nickel desulphurization has been used for the synthesis of aliphatic compounds and for structure determination. From (158) and (159) aliphatic y-diketones and y-keto-carboxylic acids have been obtained. c-Caprolactams and e-enantholactams such as (199) have been prepared by desulphurization and transformed to amino- 

Mizogami, N. Osaka, T. Otsubo, Y. Sakata, and S. Misumi, Tetrahedron Letters, 1974,799. 2 N. Osaka, S. Mizogami, T. Otsubo, Y. Sakata, and S. Misumi, Chem. Letters, 1974, 515. 

Reactions Leading to Destruction of the Thiophen Ring.— The product formed in the reaction between tetramethylthiophen and dicyanoacetylene in the presence of AlCh, and believed to be a thiepin derivative, was later shown to be a cyclobutene derivative (207) formed by a [2 + 2] cycloaddition. Thermally, (207) is rearranged to (208) by a [3,3] 

Convenient methods for the S-alkylation of thiophens with the methyl or ethyl esters of fluorosulphonic acid, or with methyl iodide and AgBp4, have been worked out. The ylide from the methyl derivative has been obtained.  

The reaction between 2-nitrothiophen and secondary aliphatic amines leads most probably to the ring-opened product (213). Raney-Nickel desulphurization continues to play an important role in the structure determination of thiophen derivatives, and for the synthesis of macrocyc-lic compounds, such as a-alkylcycloalkanones, amino-lactams of aliphatic diaminocarboxylic acids, and of dethiobiotin. The nickel boride catalyst (NiBo), prepared from nickel(ii) chloride and sodium borohydride in methanol, gives olefins in 50—55% yield. From (214) a mixture of methyl 

Guanti, C. Dell Erba, and G. Leandri, J.C.S. Chem. Comm., 1972, 1060. 

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