Synthesis of Hexahydropyridazines by [4 + 2] Cycloaddition of Donor-Acceptor Cyclobutanes and
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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. Structural assignment of the cycloadduct 3b was unambiguously established by single crystal X-ray diffraction.