Aerobic aromatization of 1,3,5-triarylpyrazolines in open air and without catalyst

Abstract

A convenient method for aerobic aromatization of 1,3,5-triarylpyrazolines to the corresponding pyrazoles by simply heating in dimethyl sulfoxide (DMSO) in an open atmosphere without catalyst is reported.

Convenient Synthesis of Pyrazolo[4′,3′:5,6]pyrano[4,3-c][1,2]oxazoles via Intramolecular Nitrile Oxide Cycloaddition

“…In addition, we investigated whether the obtained 3a,4-dihydro-3H,7H-pyrazolo [4 ,3 :5,6] pyrano [4,3-c] [1,2]oxazole system can be further oxidized. Several oxidation reaction conditions were tested, e.g., 5a was stirred in DMSO at 110 • C in an open atmosphere [56] or treated with a catalytic amount of Pd/C in acetic acid [57]; the best result was obtained using activated MnO 2 as an oxidant in toluene in a Dean-Stark apparatus for 4 h at reflux temperature [58]. Furthermore, 4H,7H-Pyrazolo [4 ,3 :5,6]pyrano [4,3-c] [1,2]oxazole derivative 6 was formed in 38% yield.…”

Multicomponent Synthesis of 4-Aryl-4,9-dihydro-1H-pyrazolo[3,4-b]quinolines Using L-Proline as a Catalyst—Does It Really Proceed?

“…The reactions published in the paper by Hedge and Shetty seemed very interesting because the obtained compounds 13 can be oxidised to give fully aromatic systems 7 (Scheme 5). An example of such a reaction is the oxidation of pyrazolines to pyrazoles, which can be performed, e.g., with oxygen in acetic acid, MnO2, DDQ or other oxidants [19][20][21]. Moreover, it can be expected that the overall yield could be greater than 33%, which is a serious shortcoming of the previous reaction described by Tomasik An example of such a reaction is the oxidation of pyrazolines to pyrazoles, which can be performed, e.g., with oxygen in acetic acid, MnO 2 , DDQ or other oxidants [19][20][21].…”

“…An example of such a reaction is the oxidation of pyrazolines to pyrazoles, which can be performed, e.g., with oxygen in acetic acid, MnO2, DDQ or other oxidants [19][20][21]. Moreover, it can be expected that the overall yield could be greater than 33%, which is a serious shortcoming of the previous reaction described by Tomasik An example of such a reaction is the oxidation of pyrazolines to pyrazoles, which can be performed, e.g., with oxygen in acetic acid, MnO 2 , DDQ or other oxidants [19][20][21]. Moreover, it can be expected that the overall yield could be greater than 33%, which is a serious shortcoming of the previous reaction described by Tomasik et al For this reason, the reactions presented in Scheme 4 were very interesting and we decided to use their potential when it comes to the synthesis of fully aromatic 1H-pyrazolo [3,4-b]quinolines [22,23].…”

Styrylpyrazoles: Properties, Synthesis and Transformations

“…The introduction of the electron-deficient nitro groups as masked amino functionalities improved the rate of the oxidative addition step and eliminated the Pd-independent side dehalogenation reaction. Both nitro groups were then converted into amine groups by iron-catalyzed reduction with hydrazine hydrate to give (E)-3,5-diamino-4-styryl-1H-pyrazoles (61). [76].…”

“…In turn, pyrazolines 15 were converted into the corresponding pyrazoles by oxidation (dehydrogenation) ( Scheme 4 ). Several oxidant agents can be employed for this transformation; some common examples include lead tetraacetate [ 58 ], DMSO in open air [ 61 ], MnO 2 [ 62 ], p -chloranil [ 63 ], 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) [ 64 ], Pd/C [ 65 ]. In 2014, Ananthnag et al developed a simple and high yielding method for the conversion of ( E )-3- and 5-styrylpyrazolines into the corresponding pyrazoles via iron(III) catalyzed aerobic oxidative aromatization [ 65 ].…”