Stereoselective Olefination Of Imines

The Wittig reaction involving direct olefination of triphenylphosphonium ylides (Ph3P=CHR) with aldehydes is arguably the most often used method for alkene synthesis. But in general, the Wittig reaction yields preferentially Z-alkenes for nonstabilized triphenylphosphonium ylides (R=alkyl) but mixtures of Z and E-alkenes for semistabilized triphenylphosphonium ylides (R=aryl or vinyl). Although a number of efforts have been devoted to the modification of the Wittig reaction, however, there remains big room for improvement with respect to the stereoselectivity and substrate scope.N-sulfonyl imines are important carbon-nitrogen double bond type compounds in organic synthesis chemisrtry. Comparing with aldehydes, the N-sulfonyl imines possess some distinct electronic and stereoselective properties. There is few report about the olefination of triphenylphosphonium ylides (Ph3P=CHR) with imines. In the course of exploring the synthetic applications of carbon-nitrogen double bond cleavage, together with our interest in stereoselective alkene synthesis, to apply carbon-nitrogen bond cleavage to selective organic synthesis, we planned to employ the sulfonyl group to activate an imine by replacing aldehydes and facilitate subsequent carbon-nitrogen bond cleavage for the highly stereoselective olefination of triphenylphosphonium ylidesA broad range of aromatic, alpha, beta-unsaturated, and aliphatic imines bearing appropriate N-sulfonyl groups smoothly undergo olefination reaction with various benzylidenetriphenylphosphoranes or allylidenetriphenylphosphoranes under mild reaction conditions to afford an array of both Z-and E-isomers of conjugated alkenes in good to excellent yields and with greater than99:1stereoselectivity. Moreover, this tunable protocol has been successfully applied to the highly stereoselective synthesis of two anticancer agents. DMU-212and its Z-isomer。Together with our interest in stereoselective alkene synthesis, a broad range of N-sulfonyl aromatic, heteroaromatic, alpha, beta-unsaturated, and aliphatic imines react with various nonstabilized phosphonium ylides to afford anarray of both (Z)-and (E)-isomers of1,2-disubstituted alkenes. allylic alcohols, and allylic amines in good yields and with greater than99:1stereoseleetivity. The Z/E selectivity for alkene svnthesis has been demonstrated to originate from the diastereoseleetive addition of nonstabilized phosphonium ylides to N-sulfonyl imines, wherein the N-sulfonyl groups serve as powerful handles to finely tune stereoselectivity.Together with our interest in stereoselective alkenyl bromides synthesis, a broad range of N-sulfonyl aromatic, heteroaromatic, alpha, beta-unsaturated, and aliphatic imines react with semistabilized phosphonium ylides to afford anarray of both (Z)-and (E)-isomers of alkenyl bromides in good yields and with greater than99:1stereoselectivity. Moreover, this tunable protocol has been successfully applied to the highly stereoselective synthesis of alkenyl chloride,and alkenyl. iodides。...