RESUMEN
The GaCl3-catalyzed [4 + 2] cycloaddition between alkoxy- and aryl-activated donor-acceptor cyclobutane diesters and cis-diazene 1a (4-phenyl-1,2,4-triazoline-3,5-dione, PTAD) is disclosed. The reaction provides hexahydropyridazine derivatives as single diastereomers in good to excellent yields in most cases. The structural assignment of the cycloadduct 3b was unambiguously established by single-crystal X-ray diffraction.
RESUMEN
Cycloadditions of strained carbocycles promoted by Lewis acids are powerful methods to construct heterocyclic frameworks. In fact, the formal [3+2] cycloadditions of donor-acceptor (DA) cyclopropanes with nitriles has seen particular success in synthesis. In this work, we report on the first [4+2] cycloaddition of nitriles with DA cyclobutanes by Lewis acid activation. Tetrahydropyridine derivatives were obtained in up to 91 % yield from various aryl-activated cyclobutane diesters and aliphatic or aromatic nitriles.
RESUMEN
Tandem ring opening, elimination, and cycloaddition of donor-acceptor cyclopropanes were observed in Yb(OTf)3-catalyzed cycloaddition with nitrosoarenes. The reaction results in formation of tetrahydro-1,2-oxazine instead of the normal cycloadduct isoxazolidine via in situ nitrone formation. A similar cascade sequence was observed with cis-diazines. Mechanistic studies on this unique transformation offer an entirely new approach for reaction design with donor-acceptor cyclopropanes.
RESUMEN
The Yb(OTf)3 catalyzed [4+2] cycloaddition between donor-acceptor cyclobutanes and nitrosoarenes is disclosed. This method facilitates the synthesis of tetrahydro-1,2-oxazines in good to excellent yields as single diastereomers. Except for a few electron-deficient nitrosoarenes, excellent regioselectivity was observed throughout these studies.