Diels-Alder reactions stereoselective

Agbossou E., Carpentier J. E. Hapiot E., Suisse I., Mortreux A. The Aminophos-phine-Phosphinites and Related Ligands Synthesis, Coordination Chemistry and Enantioselective Catalysis Coord. Chem. Rev. 1998 I78-I80 1615-1645 Keywords stereoselective Diels-Alder reaction catalysts, aminophosphine-phosphinites, enantioselective catalysts... 

Keywords stereoselectivity, Diels-Alder reaction kinetics... 

Keywords stereoselective DIels-Alder reaction catalysts, DIels-Alder chiral metallocene catalyst review... 

Keywords cationic Diels-Alder reaction, asymmetric synthesis, stereoselective Diels-Alder reaction... 

The synthesis of the macrocycles 43 (Scheme 9) is an example of repetitive, highly stereoselective Diels-Alder reaction between bis-dienes 41 and bis-dienophiles 42, containing all oxo or methano bridges syn to one another. The consecutive inter- and intramolecular Diels-Alder reactions only succeed at high pressure. Obviously, both reactions are accelerated by pressure. The macrocycles are of interest in supramolecular chemistry (host-guest chemistry) because of their well-defined cavities with different sizes depending on the arene spacer-units. 

Copper(II)-bis(oxazoline) complexes (48) are robust, valuable catalysts for a wide variety of stereoselective Diels-Alder reactions. In a key step en route to... 

K Endo, T. Koike, T. Sawaki, O. Hayashida, H. Masuda, Y. Aoyama, "Catalysis by organic solids. Stereoselective Diels-Alder reactions promoted by microporous molecular crystals having an extensive hydrogen-bonded network , J. Am Chem Soc. 1997,119, 4117-4122. 

SCHEME 2. The stereoselective Diels-Alder reaction leading to an important iodolactone prosta-glandine precursor... 

Scheme 6.133 Adducts of the 121- and 124-catalyzed stereoselective Diels-Alder reactions between the 3-hydroxypyran-2-one and the dienophiles flimaronitrile, maleonitrile, and acrylonitrile.

Enantioselective Diels-Alder reaction. Highly stereoselective Diels-Alder reactions can be achieved by use of the 4,4 -diphenylbis(oxazoline) 2b, prepared from (+)-phenylglycinol, as a chiral, bidentate ligand for iron salts. Thus reaction of Fel3 with 2b and I2 in CH3CN forms a complex presumed to be I-Fel3, which can catalyze reaction of 3-acryloyl-l,3-oxazolidin-2-one with cyclopentadiene at —50° to give the endo-adduct in 95% yield. The product is the 2R-enantiomer (82% ee). 

A highly regio- and stereoselective Diels-Alder reaction was achieved by the AUCI3 catalyzed reaction between benzofurans and phenylacetylenes with carbonyl groups at ortho positions <03AG(E)4399>. 

Diek-Alder Cycloadditions (Athene Six-Membered Cycloadduct) A-Enoylsultam derivatives were originally devised as activated chiral dienophiles for stereoselective Diels-Alder reactions. ... 

Stereoselective Diels-Alder reactions have been performed variously, using chirally modified sulfines as dienophiles, chiral ynamines, SMP enamines, SMP acrylamides, and the in situ preparation of SMP A-acylnitroso dienophiles. The [2 + 2] cycloaddition reactions of chiral keteniminium salts obtained from SMP amides with alkenes have been studied. ... 

Stereoselective Diels-Alder reactions have been reported in several cases. Enantioselective Diels-Alder reactions of l-phenoxycarbonyl-l,2-dihydropyridine with 1-alkylated acryloyl-pyrazolidin-3-ones using a chiral cationic palla-dium-phophinooxazolidine catalyst afforded chiral isoquinuclidines with excellent enantioselectivity <2005TL5677>. Bismuth(lll) chloride-mediated diasteroselective intramolecular [4-f2] cycloaddition reactions of A-allyl derivatives of pyrazole aldehydes led to fused sulfur-containing pyrazole heterocycles <2003SC3063>. A highly diastereoselective intramolecular hetero-Diels-Alder approach toward tetracyclic pyrazoles from 5-(3-methyl-2-butenylthio)-3-methyl-l-phenyl-4-pyrazolecarboxaldehyde has been reported <1997SL1155>. 

A methodology that constructs the ISQ core directly from pyridines using a 7t-basic tungsten complex to disrupt the aromatic stabilization of these inert heterocycles was recently reported [70]. For example, common pyridine derivatives, e.g., 2-dimethylaminopyridine, will undergo stereoselective Diels-Alder reactions with electron-deficient alkenes, e.g., acrylonitrile. 

Based on the experiences on the Diels-Alder reaction of 2-pyrones [20], Deng et al. have investigated the stereoselective Diels-Alder reaction of 2-pyrones and a,(3-unsaturated ketones. They also found that primary amines lo and lp derived from quinine and quinidine, respectively, werethe optimal iminium catalysts (5 mol%). The acid additive has a crucial effect on the efficiency of the reaction. TFA (20 mol%) gave the best results, and the Michael reaction, as a side reaction, could also be prohibited. 

Triorganylbismuthines can mediate such C-C bond forming reactions as shown in Scheme 5.38 in the presence or absence of a transition metal salt. Tributylbismuthine promotes the allylation of carbonyl compounds with allylic bromide [91HAC297] and the olefination of diazo compounds with carbonyl compounds in the presence of catalytic amounts of a copper(I) halide [90TL5897]. A combination of triphenylbismuthine and WCle promotes the metathesis of olefins, while a similar combination with TiC facilitates the stereoselective Diels-Alder reaction of unsaturated esters [76TMC183, 93JOC4783]. 

A stereoselective Diels-Alder reaction between furan and acrylimide yielded bicyclic adduct 32 that could be recrystalhzed to isomeric purity (Scheme 25) [84]. The cycloaddition reaction was reversible at higher temperatures and resulted in preferential formation of racemic exo isomer. Cycloadduct 32 was elaborated in six steps to e t-shikimic acid. 

Many researchers have refrained from using lanthanide complexes in stereoselective Diels-Alder reactions, perhaps due to large coordination spheres which can accommodate up to a dozen ligands. The rather daunting task of interpreting the identity of active catalysts and substrate-catalyst complexes among the myriad possible options has not hampered the development of some quite useful chiral lanthanide catalysts. 

However, complete stereochemical control of the Diels-Alder reaction to yield only disfavored exo-products in enantiomerically pure form has proven to be very difficult by chemical means. Furthermore, only recently has a potentially enzymatic Diels-Alder reaction been reported [37]. Therefore, attempts to generate antibodies which can catalyze stereoselective Diels-Alder reactions is seen as an ongoing major target in the field. 

Successful polymer supported stereoselective Diels-Alder reaction was performed using immobilized enantiopure 4-(3-hydroxy-4,4-dimethyl-2-oxopyrro-lidin-l-yl)benzoic acid 12 as a chiral auxiliary [15]. The corresponding resin-bound acrylate derivate has been applied as the dienophile 13. Preparation of the precursor started with the combination of pantolactone 10 and the sodium salt of 4-aminobenzoic acid. Conversion into the corresponding benzyl ester followed. The obtained racemate was esterified with (lS)-camphanic acid chloride to a dia-stereomeric mixture to gain the enantiopure compounds by chromatographic separation. After subsequent saponification of the camphanic acid moiety and hydrolysis of the benzyl ester the (R)-enantiomer 11 was coupled to Rink amide resin (Scheme 12.6). 

To increase the low enantiomeric excess of 40% in the stereoselective Diels-Alder reaction with isoprene, the resin-bound auxiliary was modified. After introduction of an aminohexanoic acid spacer to the chiral auxiliary, the corresponding acrylate 15 showed an enhanced ee (70%) on applying the same reaction conditions and yielded 77% (Scheme 12.8). 

Early applications of chiral Lewis acid catalyzed stereoselective Diels Alder reactions used either boron- or aluminum-derived systems in carbocyclic ring formation18 1Q, or studied the effect of chiral shift reagents, such as Eu(hfc)3, in hetero-Diels-Alder cycloadditions of carbonyl compounds to dienes20 23,77, 78. The latter type of transition metal catalyzed addition is classified as heterocarboration and is described in Section 1.5.8.4. 

Scheme 7.24 Stereoselective Diels-Alder reaction of 2-vinyl indoles with trans-enals catalysed by prolinol Im.

This methodology has been extended to include a simpler dithiolane 1,3-dioxide derivative which undergoes highly stereoselective Diels-Alder reactions giving adducts as single diastereoisomers (Scheme 4.47) [96]. 

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