(<i>S,S</i>)-3,5-Dimethylmorpholine, a Novel<i>C</i> ₂-Symmetric Auxiliary. First Application in [4+2]-Cycloadditions Leading to 4-Oxohexahydropyridazine Derivatives

Abstract

Diastereoselective Diels-Alder reactions of (S,S)-2-(3,5-dimethylmorpholino) butadienes 10 with aza-dienophiles are described, leading to cycloadducts 12 in good yields and high stereoselectivities (de = 87-96%). After double bond migration to 13, acidic and basic hydrolysis affords 4-oxohexahydropyridazine derivatives 14 and 16 of high enantiomeric purity (ee = 90-91%). The configuration of the new stereogenic centre is determined by NOE-measurements and an X-ray structure analysis of the cycloadduct (R,S,S)- 13f.