Synthesis of Hexahydropyridazines by [4 + 2] Cycloaddition of Donor–Acceptor Cyclobutanes and <i>cis</i>-Diazenes

Abstract

The GaCl₃-catalyzed [4 + 2] cycloaddition between alkoxy- and aryl-activated donor-acceptor cyclobutane diesters and <i>cis</i>-diazene <b>1a</b> (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 <b>3b</b> was unambiguously established by single-crystal X-ray diffraction.