Vinylethers substituted

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. 

Reactions of chiral vinylethers with achiral heteroatom-substituted 1-oxa-l,3-dienes displaying moderate selectivities. 

Heteroatom substituted ruthenium carbenes like 7 and 8 (Cy=cyclohexyl, i-Pr=iso-propyl) were synthesized similar to 6, just adding the appropriate vinylethers and vinylthioethers instead of styrene in the last step (Scheme 4) [20]. Phenyl vinyl sulfide was prepared according to Scheme 5a. 

Nitrone reacts with vinylethers, vinylalkyls and vinylnitrile to give major 5-substituted cjjo-products. The following examples are illustrative ... 

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