An amine-catalyzed asymmetric formal aza [3 + 3] cycloaddition of α,β-unsaturated aldehydes with N-Ts ketimines derived from both acyclic and cyclic ketones was developed, which was followed by an oxidation to afford chiral piperidine derivatives in good yields and excellent enantioselectivities (up to 99% ee). In addition, the corresponding cycloadduct piperidin-2-ols can be easily transformed to indolyl substituted chiral piperidine derivatives in good yields and excellent diastereoselectivities (>20:1) via Friedel-Crafts alkylation of indole in the presence of BF3·Et2O.Download high-res image (110KB)Download full-size image

AbstractImproved stereoselective syntheses of the target compounds (+)-valiolamine 1 and (+)-valienamine 2 starting from naturally abundant (–)-shikimic acid are described. A common key intermediate compound 7 was first synthesized from (–)-shikimic acid in 9 steps. The compound 7 was then converted to (+)-valiolamine 1 in 3 steps, and was also converted to (+)-valienamine 2 in 4 steps. In summary, (+)-valiolamine 1 and (+)-valienamine 2 were synthesized from (–)-shikimic acid in 12 (or 13) steps in 40% and 39% overall yields, respectively. The present syntheses are more practical and might be important for the potential industrial preparations of pharmaceutically valuable (+)-valiolamine 1 and (+)-valienamine 2.