Effects of 3-substituents upon orientation in the 1,3-dipolar cyclo-addition reaction between 3-substituted pyridine N-imides and ethyl propiolate: syntheses of ethyl 4- and 6-substituted pyrazolo[1,5-a]-pyridine-3-carboxylates

Characterization of Kemer L4 meteorite using Raman spectroscopy, X-ray diffraction, magnetization measurements and Mössbauer spectroscopy

“…Ethyl propiolate (HC≡CCOOCH2CH3, EP) is the ethyl ester of propiolic acid consisting of an ethyl ester group attached to an acetylenic fragment (H−C≡C−). The compound is broadly used in organic synthesis, in particular in dipolar cycloaddition reactions leading to heterocycles such as pyrazoles, which possess a large range of applications in the pharmaceutical industry as well as in the agrochemical field, [1][2][3][4][5][6][7][8][9] and as nucleophile in conjugate addition reactions such as those allowing selective carboncarbon bond formation, which are particularly relevant in chemical synthesis and molecular design. [10][11][12][13] The compound is also used as a derivatizing agent for the thiol group for the analysis of varietal thiols in wine.…”

Scalable Sonochemical Synthetic Strategy for Pyrazolo[1,5-a]pyridine Derivatives: First Catalyst-Free Concerted [3 + 2] Cycloaddition of Alkyne and Alkene Derivatives to 2-Imino-1H-pyridin-1-amines

“…Recently, numerous protocols have been evaluated for the synthesis of pyrazolo[1,5- a ]pyridines; the most common and popular route involves the intermolecular cyclization reactions of N -iminopyridinium ylides with a dipolarophile like alkynes and alkenes. 2,11−17 Moreover the intramolecular rearrangement reactions have also given rise to the formation of pyrazolo[1,5- a ]pyridine derivatives, for example, the intramolecular cyclization of ethynylpyridines 18,19 and transient nitrenes. 20,21 Recently, in our laboratory, we developed various protocols for synthesizing the pyridine derivatives and their utility as valuable precursors to synthesize a novel pyrazolo[3,4- c ]pyridine derivatives through a new distinctive [4 + 1] cycloaddition process.…”

A New Approach to Imidazo[1,2-a]pyridine Derivatives and Their Application to the Syntheses of Novel 2H-Pyrano[2’,3’:4,5]imidazo[1,2-a]pyridin-2-one Derivatives

“…Interestingly, in the reaction of unsymmetrical 3-methylpyridinium iodide (3b) only the 8-methyl derivative 4b was obtained, while the alternative 6-methyl one 4b' was not. In general, it is well known that the attack at the 2-position of the pyridine ring in the cyclization and the cycloaddition reactions of the 3-substituted pyridinium ylides or salts in the ground state is preferred over that at the 6-position, [21][22][23] but the observation of the exclusive mode at the 2-position is rare. These results are shown in Scheme 1.…”