Thieno oxadiazole

Low temperature NMR studies revealed separate signals for the isomeric thieno[2,3-c] [l,2,5]oxadiazole A-monoxide (11) and (12) at —45°C. The shielding effect of the A-oxide group... 

The energetics of the equilibrium between the isomeric thieno[2,3-c][l,2,5]oxadiazole A-mon-oxides (11) and (12) has been studied using low temperature NMR techniques, together with a comparison with other 1,2,5-oxadiazole 2-oxide systems <74JOC2956>. A similar study commented that the rate of isomerization between (13) and (14) is fast on the NMR timescale at room temperature. The equilibrium constant Kc for the isomerization between (13) and (14) is 65 whilst the free energy of activation for the isomerization is 51.3 kJ mol"1 <89JCS(P2)127>. 

Thieno[2,3-c][l,2,5]oxadiazole 1-oxide (12) was prepared in 45% yield by thermal decomposition of the azide (89a). This oxadiazole oxide (12) was also prepared, albeit in lower yield, from the amine (89b) <74JOC2956>. 

The diversity of reactions that can be performed on substituents attached to the furazan ring is well illustrated by the five-stage synthesis of the thieno[3,4-c][l,2,5]oxadiazole system (82) from the dibenzoyl compound (83 Scheme 16) borohydride reduction affords the... 

Monocyclic and Bicyclic aromatic heterocycles such as imidazoles, thiazoles, thiadiazoles, oxazoles, oxadiazoles quinazolines, indoles, benzimidazoles, purines pyrido[43-d]pyri-midines, thiazolo[5,4-d]pyrimidines, thiazolo[4,5-d]pyrimidines, oxazolo[5,4-d]pyrimi-dines and thieno[2,3-d]pyrimidines are renowned pharmacophores in drug discovery. These special structures are well explained and exemplified in chemical compound libraries. In this chapter, several types of thiazole based heterocyclic scaffolds such as mono-cyclic or bicyclic systems synthesis and their biological activities studies are presented, which are not frequently present in books and reviews. We mention the first importance of synthetic route of various thiazole based compounds and their applications in medicinal chemistry in this chapter. 

---