An efficient oxidation of 2-pyrazolines and isoxazolines by bis-bromine-1,4-diazabicyclo[2.2.2]octane complex (DABCO-Br2)

Abstract

An efficient and simple procedure has been developed for the oxidation of 1,3,5-trisubstituted 4,5-dihydro-1H-pyrazoles and -isoxazoles to their corresponding aromatic derivatives promoted by bis-bromine-1,4-diazabicyclo[2.2.2]octane complex (DABCO-Br 2 ) in acetic acid at room temperature. The products 2-pyrazoles and isoxazoles were produced in good to excellent 87-95 % and 78-95 % yields respectively.

Use of Bromine and Bromo-Organic Compounds in Organic Synthesis

“…The desired 2-pyrazoles and isoxazoles were produced in yields of 87−95% and 78−95%, respectively. 1650 DBH has also been used for the oxidation of mono-and bisurazoles to their corresponding triazolinediones in excellent yield. In this case also, the use of a solvent such as dichloromethane was found to be beneficial in increasing the product yield compared to the solvent-free process (Scheme 586).…”

“…The oxidation of 1,3,5-trisubstituted 4,5-dihydro-1 H -pyrazoles and -isoxazoles to their corresponding aromatic derivatives could be achieved using the bisbromine–1,4- diazabicyclo[2.2.2]octane complex (DABCO–Br 2 ) in acetic acid at room temperature. The desired 2-pyrazoles and isoxazoles were produced in yields of 87–95% and 78–95%, respectively . DBH has also been used for the oxidation of mono- and bisurazoles to their corresponding triazolinediones in excellent yield.…”

The versatility of DABCO as a reagent in organic synthesis: a review

“…At room temperature, 1,3,5-trisubstituted-4,5-dihydro-1 H -pyrazoles and -isoxazoles are oxidised into their respective aromatic derivatives using a DABCO–Br 2 oxidant. 109 Table 28 represents the variation of the yields of final products with change in substituents of the reactants in synthesis of 5-membered aromatic heterocycles using DABCO–Br 2 oxidant.…”

Naphtho[1,8-de][1,2]Oxazin-4-ol: Precursor to 1,2,8-Trisubstituted Naphthalenes and 1-Unsubstituted Naphtho[1,2-d]isoxazole 2-Oxide: A Novel Isomerization of the N-Oxide to Nitrile Oxide en Route to Isoxazol(in)es

“…The reactions differ by the generation mode of the nitrile oxide from the 1-naphthaldehyde oxime, by the use of PIDA [ 23 ] and oxone ® [ 24 , 25 , 26 , 27 ], or by chlorination and then dehydrochlorination [ 28 ]. 5-Aryl-3-(naphthalene-1- or 2-yl)isoxazoles have been prepared by the oxidative aromatization of 5-aryl-4,5-dihydro-3-(naphthalene-1 or 2-yl)isoxazoles [ 29 , 30 ]. 3,5-Disubstituted isoxazoles have been assembled by the 1,3-dipolar cycloaddition of appropriate nitrile oxides and arylacetylenes [ 31 , 32 , 33 ].…”