Asymmetric catalysis pericyclic reactions

BINAP, 127, 171, 191, 194, 196 olefin reaction, 126, 167, 169, 191 organic halides, 191 Pancreatic lipase inhibitors, 357 Pantoyl lactone, 56, 59 para-hydrogen, 53 Peptides, matrix structure, 350 Perhydrotriphenylene, crystal lattice, 347 Pericyclic reactions, 212 chiral metal complexes, 212 Claisen rearrangement, 222 Diels-Alder, 212, 291 ene reaction, 222, 291 olefin dihydroxylation, 150 Phase-transfer reactions asymmetric catalysis, 333... 

Enamine catalysis involves a catalytically generated enamine intermediate that is formed via deprotonation of an iminium ion and that reacts with various electrophiles or undergoes pericyclic reactions. The first example of asymmetric enamine catalysis is the Hajos-Parrish-Eder-... 

Asymmetric pericyclic reaction represents one of the most straightforward protocols to access enantioenriched cyclic compounds and triggers continuing interest in organic synthesis. Fruitful results have been achieved by the catalysis of chiral metal complexes over the past decades [1], On the other hand, recently small organic molecules have also contributed a lot to this area owing to the rapid development of asymmetric organocatalysis [2]. 

A commoner way to make heterocycles by pericyclic reactions is to use 1,3-dipolar cycloadditions. These often occur without catalysis and so are compatible with many other reactions. The starting material 182 for this asymmetric synthesis of swainsonine was derived from a natural sugar (chiral pool strategy, chapter 23). An exceptionally stereoselective Wittig reaction gave the Z-alkene 183 (chapter 15) and the alcohol was converted into the azide 184 with diphenylphos-phoryl azide.24... 

The [3+2] cycloaddition strategy provides an effective method to access valuable intermediates for the construction of biologically important alkaloids, amino acids, amino carbohydrates and P-lactams [58-62]. The reaction involves the concerted pericyclic addition of a dipole and a dipolarophile and considerable efforts have been made to render these reactions asymmetric nsing Lewis acid catalysis and chiral anxiliaries [63]. 

The nickel-iminophosphine-catalysed 4- -2-cycloaddition of enones with allenes formed highly substituted dihydropyrans. The enantioselective amine-catalysed 4-I-2-cycloaddition of allenoates with oxo-dienes produced polysubstituted dihydropyrans in high yields and with high enantioselectivities. Novel enam-ine/metal Lewis acid bifunctional catalysis has been used in the asymmetric inverse-electron-demand hetero-Diels—Alder reactions of cyclic ketones with Q ,j9-unsaturated a-ketoesters. The 4- -2-cycloaddition of acylketenes (80) with 2-unsubstituted and 2-monosubstituted 3-aryl-2//-azirines (81) produced 1 1 (82) or 2 1 (83) adducts, being derivatives of 5-oxa-l-azabicyclo[4.1.0]hept-3-ene or 5,7-dioxa-l-azabicyclo[4.4.1]undeca-3,8-diene. The formation of the monoadducts proceeds via a stepwise non-pericyclic mechanism (Scheme 25). A-heterocyclic carbene-catalysed 4- -2-cycloaddition of ketenes with 1-azadienes yielded optically active 3,4-dihydropyrimidin-2-ones (93% ee) ... 

Building upon these concepts, this chapter firstly gives an insight into the modes of action of a selection of non-covalent chiral organocatalysts, employing chiral Brpnsted acid catalysis, chiral Brpnsted base catalysis, and chiral phase-transfer catalysis (PTC). Further sections of this chapter describe two separate case studies that aim to compare and contrast selected covalent and non-covalent strategies for achieving two distinct processes, acyl transfer reactions and asymmetric pericyclic processes. 

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