Stereospecific synthesis of pyrrolidines with varied configurations via 1,3-dipolar cycloadditions to sugar-derived enones.

GUILLERMO OLIVEIRA UDRY; EVANGELINA REPETTO; OSCAR VARELA

JOURNAL OF ORGANIC CHEMISTRY

AMER CHEMICAL SOC

Lugar: Washington; Año: 2014 vol. 79 p. 4992 - 5006

0022-3263

Enantiomerically pure pyrrolidines have been obtained by 1,3-dipolar cycloaddition of stabilized azomethine ylides and sugar enones (dihydropyranones) derived from pentoses. Thus, the S-enone (menthyl 3,4-dideoxy-(1S)-pent-3-enopyranosid-2-ulose) was prepared from D-xylose, while the R analog was obtained from L-arabinose. The dipoles were generated in situ from α-aryliminoesters of common amino acids (glycine, alanine or phenylalanine) and aromatic aldehydes (benzaldehyde, 3-formylpyridine and 4-methoxybenzaldehyde). Under optimized conditions, the cycloaddition reactions were highly diastereo- and regio-selective to yield, in most of the cases, a very major adduct of the sixteen theoretically possible. The diastereoselectivity relies on the strict stereocontrol exerted by the stereogenic center of the pyranone. Thus, the (S)-enone, derived from D-xylose, gave tetrasubstituted pyrrolidines having a defined stereochemistry for the four stereocenters of the ring, while they had the opposite configuration when starting from the (R)-dihydropyranone. Furthermore, some endo-cycloadducts underwent isomerization of the carbons vicinal to the nitrogen atom to afford pyrrolidines with a rather unusual stereochemistry for the direct dipolar cycloadditions.