Inverse Diels-Alder Reactions. Synthesis of Pyranes

2 Inverse Diels-Alder Reactions. Synthesis of Pyranes 

Lewis-acid catalyzed inverse electron-demand Diels-Alder reactions between conjugated carbonyl compounds and simple alkenes and enolethers also allow dihydropyranes to be prepared. SnCU-Catalyzed cycloaddition of 

Substituted 3,4-dihydropyranes were also prepared by Diels-Alder reactions between (E)-4-oxobutenoate 80 and vinylethers [80] under iron(III) 2-ethylhex-aonate, a mild and economical catalyst (Equation 3.26). Diastereomeric excess as high as 98 % was observed. Cycloadducts with a 2,4-cw-configuration were preferred. 

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