The synthesis of unnatural pyrrolizidines has been studied using a multicomponent-domino process involving proline or 4-hydroxyproline esters, an aldehyde and a dipolarophile. The formation of the iminium salt promotes the 1,3-dipolar cycloaddition affording highly substituted pyrrolizidines under mild conditions and high regio- and diastereoselectivities.

A synthetic approach for tropane alkaloids on the basis of tandem (domino) ene-type reactions of acetone silyl enol ethers with iminium ions is shown to be triggered by intermolecular ene-type reactions followed by 6-(2,5) silatropic ene-type cyclizations.

A halogen-induced oxidative rearrangement of N,O-ketals prepared from cyclobutanones, leading to pyrrolidone derivatives, is developed. The reaction proceeds via an iminium ether intermediate and, depending on the reaction medium, two types of pyrrolidone derivative, containing a halogen atom or hydroxyl group, can be obtained.

An organocatalytic cascade reaction of 2-nitrocyclohexanone and α,β-unsaturated aldehydes was developed. Bicyclo[3.3.1]nonanone products were obtained with good yields and excellent enantioselectivities. The reaction occurred with unusual regioselectivity. A dienolate-iminium activation mechanism was proposed. The products were transformed to eight-membered cyclic ketones with high enantioselec...

The synthesis of a functionalized, tetracyclic core of N-methylwelwitindolinone C isothiocyanate is reported. The approach features a convergent coupling between an indole iminium ion and a highly functionalized vinylogous silyl ketene acetal followed by an intramolecular palladium-catalyzed cyclization that proceeds via an enolate arylation.

We have developed the first multicomponent synthesis of enantioenriched polycyclic 1,2,3,4-tetrahydropyridines bearing three contiguous stereogenic centers under iminium activation. The key to the success of this reaction was the use of polyfunctional substrates including 2-aminophenols and scarcely used β-ketoamides triggering a thermodynamically controlled regio- and diastereoselective sequence.

The first highly enantioselective hydrogenation of simple indoles was developed with a Brønsted acid as an activator to form the iminium intermediate in situ, which was hydrogenated using Pd(OCOCF(3))(2)/(R)-H8-BINAP catalyst system with up to 96% ee. The present method provides an efficient route to enantioenriched 2-substituted and 2,3-disubstituted indolines.

An unprecedented oxidant-mediated reductive amination of tertiary anilines and aldehydes without external reducing agents was developed via the nucleophilic attack of the oxygen atom of the carbonyl group to in situ generated iminium ions, in which tertiary anilines were used as both nitrogen source and reducing agent for the first time.

A range of new biphenylazepinium salt organocatalysts effective for asymmetric epoxidation has been developed incorporating an additional substituted oxazolidine ring, and providing improved enantiocontrol in alkene epoxidation over the parent structure. Starting from enantiomerically pure aminoalcohols, tetracyclic iminium salts were obtained as single diastereoisomers through an atroposelecti...

A concise sequence utilizing a Petasis three component reaction followed by a tandem aza-Cope-Mannich cyclization afforded novel polycyclic heterocycles in good yield; alternative iminium cyclization based on a Pictet-Spengler reaction or aminal formation led to divergent pathways affording skeletal diversity.