Synthesis Of Spiroisoxazolines Research Articles

Synthesis of Spiroisoxazolines via TEMPO/NaNO2-Catalyzed Aerobic Oxidative Dearomatization.

A catalytic, aerobic oxidative dearomatization protocol has been developed for the preparation of spiroisoxazline scaffolds from oximes using TEMPO and NaNO2 as the catalyst and O2 as the sole oxidant. This dearomatization methodology features its mild reaction conditions, good functional group tolerance, and an unprecedented broad substrate scope, encompassing phenols, aryl ethers, thiophenols, aryl sulfides, etc.

Synthesis of Spiroisoxazolines via an Oximation/Dearomatization Cascade under Air.

A catalytic, transition-metal-free synthesis of spiroisoxazolines is outlined. This protocol provides, for the first time, a direct access to spiroisoxazolines from aryl (thio)ethers or (thio)phenols in one synthetic step via an oximation/dearomatization cascade. In this reaction, sodium nitrite plays dual roles: as a hydroxylamine source and also a precatalyst to promote the aerobic dearomatization. This methodology features unprecedented substrate scope, high yields, promising scalability, sustainable oxidant, and mild conditions.

1,3-Dipolar cycloaddition reactions on carbohydrate-based templates: synthesis of spiro-isoxazolines and 1,2,4-oxadiazoles as glycogen phosphorylase inhibitors

1,3-Dipolar cycloaddition of aryl nitrile oxides to benzyl/acetyl-protected exo-glucals and to a benzoylated glucosyl cyanide led in high yield to spiro-isoxazolines and to 3-aryl-5-glucosyl-1,2,4-oxadiazoles, respectively. The choice of the protective groups was important to the outcome of the cycloaddition and for the deprotection of the adducts. Cleavage of the ester protecting groups (acetyl, benzoyl) provided water-soluble spiro-isoxazolines and 3-aryl-5-glucosyl-1,2,4-oxadiazoles, evaluated as glycogen phosphorylase inhibitors. Preliminary tests showed IC 50 values in the μM range.

Synthesis of spiroisoxazolines through cycloadditions of nitrile oxides with 3-methylenequinuclidine

Four spiroisoxazolines have been prepared, by cycloaddition of aceto-, pivalo-, benzo- and mesito-nitrile oxide with 3-methylenequinuclidine. The reactions were completely regioselective, within the limits of detection. None of the isoxazolines showed significant inhibition of acetylcholinesterase.

Synthesis of Spiroisoxazolines by 1,3-Dipolar Cycloaddition

The cycloaddition of the chiral nitrile oxide 1 to 1-R-substituted 3,3-methylene-5,5-dimethyl-2-pyrrolidinones 2 (where R is H, n-butyl-, 1,1-dimethylethoxycarbonyl-, 1-methylethenyl- and acetyl-) proceeds regioselectively under the formation of spiroisoxazolines, namely 7-R-substituted-6-oxo-8,8-dimethyl-1-oxa-2,7-diazaspiro[4,4]non-2-enes 5 and 6. The asymmetric induction expected by the a-chiral centre of the nitrile oxide 1 was not very effective, diastereoisomers 5 and 6 were formed in an approximate 50:50 ratio. The stereoselectivity of the 1,3-dipolar cycloaddition of the arylnitrile oxide 7 with the chiral lactam 3 and the achiral lactone 4 are investigated. The attack of the 1,3-dipole occurred from the less hindered face of the dipolarophile 3 and 4, giving the major isomer 8 and 10, respectively.