The insertion and extrusion of heterosulfur bridges. XIII. Syntheses and structural studies of nitrophenanthro[4,5‐bcd]thiophenes

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Abstract
A simplified procedure for sulfur bridging of phenanthrene (2a) with hydrogen sulfide and a catalyst, but without solvent, is described. The product, phenanthro[4,5‐bcd]thiophene (1a), undergoes nitration at 25° or 60° in acetic anhydride to give mixtures (56–79%) of 1‐nitro‐1a and 3‐nitro‐1a in varying ratios. Reductive acetylation of these nitro derivatives gives 1‐ and 3‐acetylamino‐1a (93% and 33%). Hydrodesulfurization of the former amide produces crude 1‐acetylamino‐2a. Positions of substitution are assigned primarily on the basis of nmr chemical shifts of protons ortho or peri to the nitro substituent, and are consistent with calculations of reactivity indices by simple Hückel molecular orbital theory.