Chemistry of thienopyridines. XV. Syntheses of thieno [3,4‐b] ‐ and thieno[3,4‐c] pyridines

Abstract

Thieno [3,4-b]pyridine (5) was synthesized by means of the successive steps of (a) photochlorination of 2,3-dimethylpyridine to the bis(chloromethy1) compound, (b) condensation with sodium sulfide, (c) oxidation to the sulfoxide, and (d) catalytic dehydration by means of alumina. Thien0[3,4c]pyridine (6) was obtained in an analogous manner. Spectral properties indicate that 5 and 6 have aromatic character.Of the six possible isomeric thienopyridines (1-6) syntheses on a preparative scale of 1 (4), 2 (5-7), 3 (6,7) and 4 (4,5a) have been reported in recent years. We now present details on the practical syntheses of thieno[3,4-6]pyridine (5) and thieno[3,4c]pyridine (6), originally reported in a brief communication (8). 6a3 Na3 N \ ' ' 3 1 2 3 4 5 6Prior to our studies parent compounds 5 and ti were unknown. Russian workers (9) had reported the condensation of a 3-aminothiophene salt with methyl vinyl ketone to give a mixture of 7-methyl-4 and 7-methyl-5. However, repetition of this reaction and structural studies on the two isolable products (4) indicated that one obtains a mixture of 5and 7-methyl-4, instead. Recently, Spinner and Yeoh (10) reported syntheses of derivatives OH (7) of the 1,3-dihydro-5 system. Treatment of 7a and 7b with acetic acid-hydrogen peroxide gave the corresponding sulfones. Methylation of 7a (with diazomethane) formed 8b, while methylation of 7b (with methyl iodide) gave a product to which an S-methyl structure was assigned. The sulfone of 8b, plus studies on ionization constants and tautomerization of hydroxy compounds, were also described.

Synthesis and Characterization of Poly(pyridine vinylene) via the Sulfinyl Precursor Route

“…Monomer Synthesis. The monomer synthesis (see Scheme ) started from the commercially available 2,5-lutidine, which was chlorinated with N -chlorosuccinimide . Dichloride 2 is unstable at room temperature and decomposes spontaneously to an unknown red substance; however, it can be stored at −25 °C for longer periods without degrading.…”

“…The monomer synthesis (see Scheme 1) started from the commercially available 2,5lutidine, which was chlorinated with N-chlorosuccinimide. 9 Dichloride 2 is unstable at room temperature and decomposes spontaneously to an unknown red substance; however, it can be stored at -25 °C for longer periods without degrading. The thioether group is introduced in a two-phase reaction using 1-octanethiol, sodium hydroxide, and a phase transfer reagent, Aliquat 336.…”

Regioselectivity in free radical bromination of unsymmetrical dimethylated pyridines

“…Many examples of side-chain free-radical halogenation of N-heterocyles have been reported in literature. 24,25,102,103 The major product by the radical bromination reaction of 2,3-dimethyl pyridine with NBS obtained was 3-(bromomethyl)-2-pyridine reported in the literature. Thus obtained monobrominated product (70) was precursor for the preparation of regioisomeric sulfide (71).…”