Synthesis by Ring-closure Reactions

Synthesis of Thiophens by Ring-closure Reactions.—The reaction of dipotassium nitroethylenedithiolate and a-chlorocarbonyl derivatives, followed by oxidation with iodine, gave (1). Treatment of pentane-2,4-dione with carbon disulphide in the presence of potassium hydroxide, followed by treatment with ethyl bromoacetate, methyl iodide, and alkali, gave (2). Compounds of type (3) were formed in the reaction of 1-cyanomethylpyridinium chloride with carbon disulphide and alkylating agents such as chloroacetonitrile, ethyl bromoacetate, phenacyl bromide, or chloroacetamide in the presence of alkali, and intramolecularly cyclized to (4). After 5-methylation, the pyridine ring could be cleaved by reaction with phenylsulphonylacetonitrile and alkali in DMSO 

The reaction of vinylacetylene with sodium sulphide and sodium hydrosulphide in DMSO-sodium or potassium hydroxide and water has been studied in detail. The products formed were (17), (18), and (19). Conditions for selectively obtaining (17) or (19) have been worked out, while (18) was only formed in 25% yield. Interestingly, thiophen is the main product from the reaction of vinylacetylene with sulphide ions generated from elemental sulphur. The formation of thiophen appears not to be caused by oxidation of (19) by elemental sulphur.  

---

I.3.2.2.3. 1,3-Diazepines Fnsed to Heteroaromatic Rings Synthesis by Ring-Closure Reactions... 

---