Short enantioselective approach to substituted triazolopyridazines from [(S)R]-1-(1E, 3E)-1-p-tolylsulfinyl-1,3-pentadiene

Enantiomerically pure hydroxy substituted triazolopyridazine 5a was obtained in one pot under mild conditions by reaction of (+)-( R )-(1 E ,3 E )-1-( p -tolylsulfinyl)-1,3-pentadiene and 4-methyl-1,2,4-triazoline-3,5-dione in the presence of P(OMe) 3 . The process involved a tandem Diels-Alder cycloaddition/sulfoxide-sulfenate rearrangement and trapping of the intermediate sulfenate.