In organic chemistry, atoms other than carbon and hydrogen are generally referred to as heteroatoms. The most common heteroatoms are nitrogen, oxygen and sulfur. Now I present to you an article called Introduction of heterocycles at the 2-position of indoline as ester bioisosteres, published in 2004-02-20, which mentions a compound: 50501-07-0, mainly applied to indoline heterocyclic derivative preparation cyclization, Quality Control of Ethyl indoline-2-carboxylate.
Compounds were prepared with heterocyclic replacements for metabolically unstable esters of benzopyranyl indole-2-carboxylic esters, which showed good in vitro and in vivo cardioprotective efficacies possibly through the opening of mitochondrial ATP-sensitive potassium channel (KATP). Initially, indolin-2-yl-heterocycles were constructed using unprotected indoline-2-carboxylic acid, but the cyclization was proceeded with oxidation of the indoline ring to the indole, which did not react with benzopyranyl epoxide. An N-BOC group was introduced to deplete the electron d. of the indoline ring. Various indolin-2-yl-heterocycles, such as I and II, were prepared by the cyclization of the building blocks including carboxamide, β-hydroxy amide, hydrazide, nitrile starting from N-BOC-indoline-2-carboxylic acid.
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Reference:
Tetrahydropyran – Wikipedia,
Tetrahydropyran – an overview | ScienceDirect Topics