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THERMAL AND CATALYTICAL TRANSFORMATIONS OF 5-ISOXAZOLIDINOLS

THERMAL AND CATALYTICAL TRANSFORMATIONS OF 5-ISOXAZOLIDINOLS. Cornelia Uncuta, Emeric Bartha, Anca Tanase, Daniela Vuluga, Silvia Udrea and Andreea Corbu Center of Organic Chemistry “C.D. Nenitzescu”, Romanian Academy, Spl. Independentei 202B, Bucharest 060023, ROMANIA.

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THERMAL AND CATALYTICAL TRANSFORMATIONS OF 5-ISOXAZOLIDINOLS

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  1. THERMAL AND CATALYTICAL TRANSFORMATIONS OF 5-ISOXAZOLIDINOLS Cornelia Uncuta, Emeric Bartha, Anca Tanase, Daniela Vuluga, Silvia Udrea and Andreea Corbu Center of Organic Chemistry “C.D. Nenitzescu”, Romanian Academy, Spl. Independentei 202B, Bucharest 060023, ROMANIA Thermal isomerization and demethanation of 4-isoxazoline 3 5-Isoxazolidinols through Michael addition of hydroxylamine to conjugated enones 3 E,Z-6 7 Conditions in thermolysis Yield T(°C)/Solvent Duration(h) E,Z-6 7 110°/ toluene 6 60% 20% 110°/ xylene 15 ― 55% 1 2 2’ 1 R1 R2 R3 Yield Tautomeric composition (%) (in CDCl3, by 1H-NMR) a Me Me Me 91 ― 2’a(100%) E-b Ph Me Ph 82 2b(2%) E,Z-2’b(98%) E-c Ph H Ph 20 2c(100%) ― d H2C CH2 Me 25 2d-oxime ― Stereochemistry of compound 4 • Number of stereoisomers: • - theoretical: 10; • isolated and detected by chiral HPLC: 2 enantiomeric pairs, labeled (±)A, (±)B. Original observation: hindering of rotation for the phenyl groups at the ketalic center.( ) Experimental proof: chemical shift nonequivalence of o,o’- and m,m’- positions in both 1H- and 13C-NMR spectra (CDCl3, room temp.) Dehydration (intra vs intermolecular) under acidic catalysis E,Z-2’b 3 4 (±)A Catalyst Time Yield 3 4 1% 1h quant ― 10% 1h 30% 20% 2’a 5 (±)B 1% 2.5h 55% 5 MS: 244[M+], 114 (70%), 72 (100%), 56 (48%), 43 (86%) Financial support: CERES PROGRAMME, Romanian Ministry of Education and Research

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