Reductions, Reductive Alkylations, and Intramolecular Cyclizations of Acyl Silanes with Samarium Diiodide or Tributyltin Hydride

The Synthesis of N-(1-Allyl-3-Butenyl)-N-Aryl Amines by Addition of Organosamarium Reagents to Formanilides

N-(1-allyl-3-butenyl)-N-aryl amines have been prepared for the first time in good yield via the direct diallylation reaction of formanilides with an organosamarium reagent under mild conditions.

Stereoselective synthesis of delta-lactones from 5-oxoalkanals via one-pot sequential acetalization, Tishchenko reaction, and lactonization by cooperative catalysis of samarium Ion and mercaptan

By the synergistic catalysis of samarium ion and mercaptan, a series of 5-oxoalkanals was converted to (substituted) delta-lactones in efficient and stereoselective manners. This one-pot procedure comprises a sequence of acetalization, Tishchenko reaction and lactonization. The deliberative use of mercaptan, by comparison with alcohol, is advantageous to facilitate the catalytic cycle. The reaction mechanism and stereochemistry are proposed and supported by some experimental evidence. Such samarium ion/mercaptan cocatalyzed reactions show the feature of remote control, which is applicable to the asymmetric synthesis of optically active delta-lactones. This study also demonstrates the synthesis of two insect pheromones, (2S,5R)-2-methylhexanolide and (R)-hexadecanolide, as examples of a new protocol for asymmetric reduction of long-chain aliphatic ketones.

Samarium Ion-Promoted Cross-Aldol Reactions and Tandem Aldol/Evans-Tishchenko Reactions

Cross-aldol reactions of carbonyl compounds were achieved by the catalysis of SmI(2) or SmI(3), together with molecular sieves, at ambient temperature. 1,3-Dichloroacetone and 1-chloroacetone can be used as acceptor substrates in the cross-aldol reactions with donor substrates such as acetone, cyclopentanone, and cyclohexanone. The cross-aldol reactions with (R)-glyceraldehyde acetonide gave optically pure compounds 25-32, the stereochemistry of which was in agreement with a chairlike chelate transition state of dipolar mode. SmI(2)-molecular sieves or SmI(3)-molecular sieves also functioned as effective Lewis acids to catalyze tandem aldol/Evans-Tishchenko reactions. The aldol/Evans-Tishchenko reactions of methyl ketones with aldehydes occurred at 0 degrees C to give alpha,gamma-anti diol monoesters 53a-59a. When the reactions were conducted at room temperature, a certain degree of transesterification took place. The aldol/Evans-Tishchenko reactions of ethyl or benzyl ketones with aldehydes yielded alpha,beta-anti-alpha,gamma-anti diol monoesters 60a-65a. However, the aldol/Evans-Tishchenko reactions of cyclic ketones with benzaldehyde occurred with a different stereoselectivity to give alpha,beta-syn-alpha,gamma-anti diol monoesters 66a-76a. The structures of products were determined by chemical and spectroscopic methods including an X-ray diffraction analysis of 72a derived from the reaction of 4-tert-butylcyclohexanone and benzaldehyde. A reaction mechanism involving dissociation-recombination of aldols followed by intramolecular stereoselective hydride shift is proposed, based on some experimental evidence, to explain the dichotomous stereoselectivity using acyclic or cyclic ketones as the reaction substrates.