Catalytic Enantioselective Inverse-Electron Demand 1,3-Dipolar Cycloaddition Reactions of Nitrones with Alkenes

C1-Symmetrical Ti(OTos)2- and TiCl2-TADDOLate-catalysed 1,3-dipolar cycloaddition reactions of nitrones to electron-deficient alkenes

A regio-, diastereo- and enantioselective 1,3-dipolar cycloaddition reaction between nitrones and electron-deficient alkenes has been developed employing C1-symmetrical Ti(OTos)2- and TiCl2-TADDOLate as catalysts. In the presence of powdered 4 Å molecular sieves and 100 mol% of Ti(OTos)2-TADDOLate as the catalyst, the nitrones smoothly react with alkenes at room temperature to give isoxazolidines in high conversion, giving the trans-diastereomer of the isoxazolidines with de's up to >90% and ee up to 58%. Furthermore, C1-symmetrical TiCl2-TADDOLate has a better chiral induction, giving the trans-diastereomer of the isoxazolidines with high enantioselectivity up to 70% ee. The influence of catalyst amount, temperature and solvents on the reaction course has been investigated

1,3-Dipolar cycloaddition on solid supports: nitrone approach towards isoxazolidines and isoxazolines and subsequent transformations

1,3-dipolar cycloaddition reactions of nitrones with alkenes and alkynes are well-studied reactions in solution-phase organic chemistry. However, the number of studies concerned with their application in solid-phase organic synthesis is rather low compared to other 1,3-dipoles, e.g. azides or nitrile oxides. This tutorial review aims to summarise the main approaches towards the application of nitrones in 1,3-dipolar cycloaddition reactions on solid supports in addition to subsequent transformations with polymer-bound isoxazolidines and reactions using polymer-bound catalysts.

Diastereoselectivity-Switchable and Highly Enantioselective 1,3-Dipolar Cycloaddition of Nitrones to Alkylidene Malonates

Trisoxazoline 1/Co(ClO(4))(2).6H(2)O catalyzed the 1,3-cycloaddition between nitrones 3 with alkylidene malonates 2 at 0 degrees C to give the isoxazolidines with both high enantioselectivity and high exo selectivity. However, when the temperature was lowered from 0 to -40 degrees C, the same cycloaddition afforded endo isomers as the major products with good to high enantioselectivity. A mechanism is provided.

Enantioselective 1,3-dipolar cycloaddition of nitrones catalyzed by optically active cationic cobalt(III) complexes

[reaction: see text] The optically active beta-ketoiminato cationic cobalt(III) complexes were employed as efficient Lewis acid catalysts for the enantioselective 1,3-dipolar cycloaddition reaction of alpha,beta-unsaturated aldehydes with nitrones. Excellent endo selectivities and high enantioselectivities were achieved in the cycloaddition reaction of 1-cyclopentene-1-carbaldehyde and the nitrones derived from 2-halobenzaldehyde.

Tetranuclear titanium 7,7'-modified binaphtholate cluster as a novel chiral Lewis acid catalyst

Chiral tetranuclear Ti cluster, a cubic structure constituted of four Ti atoms and OHs, and six (R)-binaphthols (BINOL) bridged two Ti atoms as ligands, is shown to be a novel chiral Lewis acid catalyst for the [2+3] cycloaddition reaction with nitrones. The chiral Ti clusters with 7,7'-substituted (R)-BINOL ligands was synthesized to give enhanced enantiomeric excesses up to 78% ee.

First asymmetric synthesis of quinoline derivatives by inverse electron demand (IED) Diels-Alder reaction using chiral Ti(IV) complex

[reaction: see text] (R,R)-3-Aza-3-benzyl-1,5-dihydroxy-1,5-diphenylpentane (1) ligated Ti(IV) complex (1-TiCl(2)) is used as a chiral Lewis acid catalyst for promoting asymmetric IED Diels-Alder reaction between electron-rich dienophiles and electron-poor dienes. Here we introduce a facile route for the synthesis of asymmetric tetrahydroquinoline derivatives using the above-mentioned chiral catalyst reagent in the presence of 4 A molecular sieves. The reactions proceed with moderate yields and at times high enantioselectivty.

Catalytic enantioselective 1,3-dipolar cycloaddition reactions of cyclic nitrones: a simple approach for the formation of optically active isoquinoline derivatives

The first highly diastereo- and enantioselective catalytic 1, 3-dipolar cycloaddition reaction of cyclic nitrones activated by chiral Lewis acids with electron-rich alkenes has been developed. The nitrones, mainly 3,4-dihydroisoquinoline N-oxides, are activated by chiral 3,3'-aryl BINOL-AlMe complexes and undergo a regio-, diastereo-, and enantioselective 1,3-dipolar cycloaddition reaction with especially alkyl vinyl ethers, giving the exo diastereomer of the cycloaddition products in high yield, >90% de and up to 85% ee. The reaction has been investigated under various conditions, and it is demonstrated that the reaction is an attractive synthetic procedure for the introduction of a chiral center in the 1-position of the isoquinoline skeleton. The mechanism of the reaction is discussed on the basis of the assignment of the absolute configuration of the cycloaddition product and theoretical calculations.