Abstract
The high-pressure promoted cycloadditions of enol ethers (1) and alkyl 3-aryl-2-cyano-2-propenoates (2) lead stereoselectively in high yields to 2,6-dialkoxy-4-aryl-3,4-dihydro-2H-pyran-5-carbonitriles (3). These cycloadducts have a high potential for further synthesis due to the presence of various functionalities. This is illustrated with some representative conversions. As reactive cyclic ketene acetals the cycloadducts 3 were easily hydrolyzed to aldehydes (6) or ketones or alcoholized to acetals having additional ester and cyano groups (5). Removal of the ester group by decarboxylation gave γ-cyano acetals (7), which were further reduced to δ-amino acetals (8). Selective reduction of the cyano group gave access to acetals of β-amino acid esters (9). The potential of such amino acid esters is demonstrated in a straightforward synthesis of a paroxetin precursor 17 from 13. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)
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