High-pressure promoted cycloadditions of enol ethers and 3-aryl-2-cyano-2-propenoates
Aben RWM, de Gelder R, Scheeren HW
EUROPEAN JOURNAL OF ORGANIC CHEMISTRY (18): 3126-3132 SEP 2002

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 gamma-cyano acetals (7), which were further reduced to delta-amino acetals (8). Selective reduction of the cyano group gave access to acetals of beta-amino acid esters (9). The potential of such amino acid esters is demonstrated in a straightforward synthesis of a paroxetin precursor 17 from 13.