Funktionalisierung von 6H-1,2-Oxazinen durch 1,3-dipolare Cycloadditionen und Halogenierungen

6H-1,2-Oxazines were functionalised at the C-C double bond by 1,3-dipolar cycloadditions and halogenation reactions. The reactions were carried out with 6-ethoxy-3-phenyl-6H-1,2-oxazine, 6-ethoxy-3-ethoxycarbonyl-6H-1,2-oxazine and 6-ethoxy-3-trifluoromethyl-6H-1,2-oxazine. The cycloadditions of 6H-1,2-oxazines were performed with nitrile oxides, nitrile imines, nitrile ylides, diazoalkanes, azomethine ylides and a nitrone. High diastereoselectivity was observed, induced by the steric hindrance of the ethoxy group at the 6H-1,2-oxazines. The cycloadditions occur with high regioselectivity. In addition, the constitutions of the bicycles were predicted by the frontier-orbital model using the semi-empirical PM3-method, and subsequently compared with those of the isolated products. The low strength of the N-O bond of 1,2-oxazines can often be used for mild hydrogenolysis reactions, but the reductions of the biheterocycles obtained here were not selective and led in most cases to decomposition. For the derivatives of 3-ethoxycarbonyl-3a,7a-dihydro-4H-isoxazolo[5,4-d]-1,2-oxazine the conversion of the five-membered ring into cis-configurated α-hydroxynitriles (saponification and decarboxylation) was demonstrated. Finally, the 4-chloro- and 4-bromo-6H-1,2-oxazines were prepared in good yields. Investigations with palladium catalysed coupling reactions were initiated. The halogen of 4-bromo-6H-1,2-oxazines was substituted by the phenyl group of benzolboronic acid using the Suzuki method.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Technische Universität Dresden

Year

2001

Author dc:creator

• Schmidt, Elmar

Contributors dc:contributor

• Reißig, Hans-Ulrich
• Liebscher, J.
• Fabian, J.

• 4-Brom-6H-1,2-oxazine
• 4-Chlor-6H-1,2-oxazine
• 4H-1,2-Oxazine
• 6H-1,2-Oxazine
• 4-Bromo-6H-1,2-oxazines
• 4-Chloro-6H-1,2-oxazines
• 4H-1,2-Oxazines
• 6H-1,2-Oxazines