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.
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