The first organocatalytic addition of β-ketosulfones to nitroalkenes catalyzed by thiourea cinchona alkaloids is presented. The readily obtained addition products were selectively transformed into chiral nitrones by reduction of the nitro group and in situ cyclization (up to 99:1 e.r. and >98:2 d.r.). Moreover, the utility of this method has additionally been demonstrated by the further transformation to functionalized N-hydroxypyrrolidines that possess a quaternary center by addition of trimethylsilyl cyanide (TMSCN) to the C=N bond of the cyclic nitrones in the presence of a Lewis acid.

Synthesis of Chiral Cyclic Nitrones by Asymmetric Addition of β-Ketosulfones to Nitroalkenes Followed by Reductive Cyclization. -The addition step is catalyzed by thiourea cinchona alkaloids like (I) to give the sulfone addition products as diastereomeric mixtures. The following reduction step proceeds selectively in the presence of activated zinc/ammonium chloride. The method can be extended to the synthesis of N-hydroxypyrrolidines (VII) bearing a quaternary stereocenter by addition of TmsCN to the C=N bond of the cyclic nitrones in the presence of a Lewis acid. -(GARCIA MANCHENO*, O.; TANGEN, P.; ROHLMANN, R.; FROEHLICH, R.; ALEMAN, J.; Chem. Eur. J. 17 (2011) 3, 984-992, http://dx.

No abstract