No abstract

Sulfur bridging inlo the phenylpyridines, 2‐ and 3‐phenylquinolines, and the symmetric bi‐pyridines was effected by means of hydrogen sulfide and an alumina catalyst at 630° to give [1]benzothienopyridines, [1]benzothienoquinolines, and thienodipyridines, respectively. Structures of products were assigned on the bases of spectral and chromatographic studies, as well as of separate syntheses. Relative yields of the various products are rationalized in terms of a model for interaction between a chemisorbed sulfur atom and the substrate molecule.

No abstract

Treatment of phenanthrene with hydrogen sulfide and an alumina catalyst at 630° gives phenthro[4,5‐bcd]thiophene (XVII). Spectral properties of XVII, its sulfoxide, and its sulfone are presented. Other examples of the direct insertion of a sulfur bridging atom into an aromatic molecule are reviewed.

No abstract

No abstract

Thieno[ 2,3‐b]pyridine (I) and thieno[3,2‐b]pyridine (II) were nitrated at C‐3 in ca. 50% yield by means of nitric‐sulfuric acids. Reduction of 3‐nitro‐I (Ia) with tin and hydrochloric acid gave 3‐amino‐I (Ib) (39%), which was converted to 3‐acetylamino‐I (Ic) and to dipyrido[2,3‐b:2′,3′‐d]thiophene (V). Reduction of 3‐nitro‐II (IIa) with iron and acetic acid at 100° gave 3‐acetyl‐amino‐II (IIb) (25%), while use of tin and hydrochloric acid at room temperature gave 2‐chloro‐3‐amino‐II (IIc). Assignments of position of nitration are based on nmr spectral data (which indicate. that substitution occurs in the thiophene ring) and on non‐identities of Ic, IIb, and V with authentic samples of 2‐acetylamino‐I, 2‐acetylamino‐II, and dipyrido[2,3‐b:3′,2′‐d]thiophene (VI), respectively. Results are consistent with reactivity indices for I and II as calculated from simple Hückel Molecular Orbital theory and with observations on nitration and reduction in the isoteric quinoline system.

A study was made of the formation of thieno[2,3‐c]pyridine (1) from hydrogen sulfide and 4‐vinylpyridine in a flow system at 630°. 2‐(4‐Pyridyl)ethanethiol and bis‐2‐(4‐pyridyl)ethyl sulfide were found to be likely intermediates. Based on these studies, there was devised a two‐step practical preparative method for I (optimum overall yield 58%) which consists of preliminary conversion of 4‐vinylpyridine to benzyl 2‐(4‐pyridyl)ethyl sulfide and subsequent thermolysis (at 605°) of this substance.