Stereoselective Diels-Alder Reaction Research Articles

ChemInform Abstract: Diethylaluminum Ethoxide Mediated Stereoselective Diels—Alder Reaction of α,β‐Unsaturated Ketones and Acetoxy‐1,3‐butadienes as Diene Components.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Diethylaluminum Ethoxide Mediated Stereoselective Diels-Alder Reaction of α,β-unsaturated Ketones and Acetoxy-1,3-butadienes as Diene Components

Abstract Stereoselective Diels-Alder reaction between several α,β-unsaturated ketones and acetoxy-1,3-butadienes is effectively performed by the promotion of diethylaluminum ethoxide under mild conditions. This reaction is successfully applied to the synthesis of optically active bicyclo[6.4.0]dodecanone 9 which corresponds to the BC ring system of 10-deoxy taxane derivatives from the 8-membered ring enone 7 and diene 2.

ChemInform Abstract: Stereoselective Diels—Alder Reaction of Electrogenerated Quinones on a PTFE‐Fiber Coated Electrode in Lithium Perchlorate/Nitromethane.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Cyclic BF2 Adducts of Functionalized Fischer Vinylcarbene Complexes: Preparation and Stereoselective Diels—Alder Reactions with 2‐Amino 1,3‐Dienes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Stereoselective Diels-Alder reaction of electrogenerated quinones on a PTFE-fiber coated electrode in lithium perchlorate / nitromethane

Diels-Alder reaction of dienes and in situ generated quinones was accelerated on a PTFE-fiber in an electrolytic lithium perchlorate / nitromethane system. In the presence of PTFE-fiber on a glassy carbon electrode, unstable quinones were efficiently generated by electrooxidation and trapped by dienes maintained on the poly-fluorinated fiber to give the desired cycloadducts stereoselectively in excellent yields.

1,3-Dipolar Cycloaddition Reactions of trans-2-Methylene-1,3-dithiolane 1,3-Dioxide with Nitrones

The 1,3-dipolar cycloaddition reaction between a nitrone and an olefinic dipolarophile is an efficient method for the synthesis of the isoxazolidine ring system (Figure 1).1 Furthermore, the cycloadducts have found numerous applications in synthesis through reductive cleavage of the N-O bond to give γ-amino alcohols.1 Asymmetric induction in nitrone-olefin cycloadditions has been achieved through incorporation of chirality in both the dipole and dipolarophile.2,3 More recently, advances have been made in the use of metals to influence the rate, regioselectivity, stereoselectivity, and enantioselectivity of the reaction through suitable combinations of metal/ dipole/dipolarophile, effectively overcoming the tendency of nitrones to form inactive dipole/Lewis acid complexes.4 In comparison to the Diels-Alder reaction, the 1,3dipolar cycloaddition of nitrones with olefins generally exhibits lower levels of regioand stereocontrol (exo/endo selectivity), a consequence of significant contributions by both LUMO (dipole)-HOMO (dipolarophile) and HOMO (dipole)-LUMO (dipolarophile) interactions, further complicated by the possibility of interconversion of the nitrone geometry in the case of acyclic nitrones.1 Therefore, despite the advances outlined above, there still remains a need to develop general systems that give predictably high levels of regioand stereocontrol with a range of nitrones. Herein we describe one potential solution to this problem. We have recently reported an asymmetric synthesis of the C2-symmetric cyclic alkenyl sulfoxide (1R,3R)-2methylene-1,3-dithiolane 1,3-dioxide 1 (Figure 2).5 The presence of a C2 symmetry element in 1 means that the exo/endo approaches of 1 to a diene are symmetry related and therefore identical, thereby reducing the number of competing transition states in the reaction. Indeed, 1 showed very high reactivity and stereoselectivity in Diels-Alder reactions with a range of dienes, and after hydrolysis of the bis-sulfoxide moiety of the cyclopentadiene adduct 2, enantiomerically pure norbornenone 3 was obtained. Thus, we were able to demonstrate 1 to be an effective chiral ketene equivalent.5 To the best of our knowledge the potential advantage of using a C2symmetric dipolarophile to overcome the exo/endo issue in 1,3-dipolar cycloaddition chemistry has not been exploited. We report herein our results of the cycloaddition of 1 with some acyclic and cyclic nitrones.

Iron(III) 2-ethylhexanoate as a novel, stereoselective hetero-Diels–Alder catalyst

Iron(III) 2-ethylhexanoate has been used as a novel, mild Lewis acid catalyst for the stereoselective Diels–Alder reaction of ethyl (E)-4-oxobutenoate with alkyl vinyl ethers to stereoselectively produce cis-2-alkoxy-3,4-dihydro-2H-pyran-4-carboxylic acid, ethyl esters with diastereoisomeric excesses (de) as high as 98%.

Chemo‐, Regio‐, and Stereoselective Diels–Alder Reaction of Ambident Dienophilic Monothiomaleimide

AbstractBoth the CS and CC functionalities of N‐arylmonothiomaleimides readily undergo a [4 + 2] cycloaddition reaction at ambient temperatures with both electron‐donating and ‐withdrawing dienes. The CS groups of N‐arylmonothiomaleimides are generally more reactive than the CC groups, especially toward dienes bearing conjugation and electron‐attracting groups, and provide mixtures of ortho,endo products 3 and ortho,exo products 4 with complete regioselectivity (100% ortho) and with high stereoselectivity (more than 86% endo). The CC groups, on the other hand, display a high stereoselectivity (100% endo) but a low regioselectivity, providing ortho,endo adducts 5 and meta,endo adducts 6 in ratios ranging from 1:1 to 6:1. Compared with N‐phenylmonothiomaleimide (1). N‐p‐nitrophenylmonothiomaleimide (11a) is more reactive and displays a higher CS vs. CC chemoselectivity in favor of CS, while N‐p‐anisyl (11b) and N‐benzyl (11c) derivatives display quite the reverse reactivity and selectivity. N‐Phenylmonothiocitraconimide (11d) serves as a CS specific dienophile and reacts with dienes to furnish ortho,endo adducts 12 with excellent regio‐ and stereoselectivities (100% ortho,endo). Both hard (BF3 · OEt2, TiCl4) and soft (CuBr · SMe2) Lewis acids enhance the reaction rate enormously and increase chemoselectivity in favor of CS. The chemo‐ (CS/CC), regio‐ (ortho/meta) and stereochemical outcomes (endo/exo) are rationalized by transition structure analysis based on AM1 calculation.

Stereoselective synthesis of concave spacers for long-range electron transfer models

Syntheses of concave spacers ( 9, 27) proceeded via stereoselective Diels-Alder reactions. Successful preparation of asymmetrical spacer 27 relied on regioselective protection of mutual precursor 7.

Diastereoselective synthesis of (1S,2S,3R,4R) and (1R,2S,3R,4S)-bicyclo[2.2.1]hept-2-amino-2,3-dicarboxylic acids: New conformationally-constrained (S)-aspartic acid analogues

Abstract The title compounds were prepared from key intermediates readily obtained by the stereoselective Diels-Alder reaction of ( Z )-2-phenyl-4-[( S )-2,2-dimethyl-1,3-dioxolan-4-ylmethylene]-5(4H)-oxazolone, a chiral az-lactone derived from ( R )-glyceraldehyde and cyclopentadiene.

Highly stereoselective hetero Diels-Alder reactions of chiral 3-(p-tolylsulfinyl)-2-furaldehyde with Danishefsky's diene promoted by a lanthanoid Lewis acid

Abstract Hetero Diels-Alder reactions of optically active 3-(p-tolylsulfinyl)-2-furaldehyde with 1-methoxy-3-(trimethylsilyloxy)-buta-1,3-diene (Danishefsky's diene) in the presence of a Lewis acid has been examined. The reaction in the presence of 1.0 equiv. of Ln(OTf)3 (Ln = Yb, Nd and Sm) followed by acidic work-up produced in good yields (68–88%) the hetero Diels-Alder adduct with high diastereoisomeric excesses (93–98% d.e.'s), whereas in the presence of an NMR shift reagent, tris(2,2,6,6-tetramethyl-3,5-heptanedionate)europium [Eu(thd)3] the corresponding diastereoisomer was obtained as the major adduct in excellent yield with 77% d.e.

A novel approach to 2-amino-1,3-dienes by coupling of α-chloro enamines and alkenyl lithium compounds

Coupling of α-chloro enamines as key building blocks with alkenyl lithium compounds lead to the formation of 2-amino-1,3-dienes 6. These cross conjugated enamines constitute important diene components for stereoselective Diels-Alder reactions and were prepared in 32–75% overall yield starting from the corresponding amides.

The role of hard Lewis acids in the tunning of the exo/endo stereoselectivity in Diels-Alder reactions: ab initio calculations

Recent experimental studies (D.C. Bradock, J.M. Brown and P.J. Guiry, J. Chem. Soc., Chem. Commun., (1993) 1244) on the stereoselectivity of the Diels-Alder reaction of thionofumarate derivatives with cyclopentadiene show that the hard or soft character of the Lewis acid catalysts can play a very important role controlling the steric course of this type of cycloaddition. RHF/3-21G ∗ ab initio calculations allow one to obtain a qualitatively correct description of the stereochemical outcome of that reaction both in the thermal and in the (hard) Lewis acid-catalysed cases.

Dispiroketals in synthesis (Part 13): Functionalised dispiroketals as new chiral auxiliaries; highly stereoselective diels-alder reactions using a bifunctional, C 2- symmetrical chiral auxiliary

Highly selective, asymmetric, Lewis acid catalysed Diels-Alder reactions are reported with a bifunctional, C 2-symmetrical diacrylate derivative obtained from a chiral auxiliary based on dihydroxylated dispiroketals.

Facile, regio and stereoselective Diels-Alder reactions of allenic trichloromethyl sulfones and sulfoxides

The dienophilic reactivity of allenes is drastically increased by the powerful electron withdrawing trichloromethylsulfonyl or sulfinyl substituents. The [4+2]-cycloadditions proceed smoothly with high regio- and stereoselectivity under mild conditions. Using an optically active allenyl sulfone, transfer of chirality has been observed.

A novel reaction of coordinated vinylidenes: coupling with hydrogen sulfide to give a η1-thioaldehyde

The RuII fragment [(PNP)RuCl2] assists the coupling of phenylacetylene with H2S to give 2-phenylethanethial [PNP = CH3CH2CH2N(CH2CH2PPh2)2] in a reaction that is initiated by alk-1-yne to vinylidene tautomerism at ruthenium, followed by electrophilic attack of H2S on the vinylidene ligand; 2-phenylethanethial is recovered as either η1-S-ligand or endo-6-benzyl-1-thiabicyclo[2.2.1]hept-3-ene ligand, and the latter molecule is formed via a stereoselective Diels–Alder reaction between cyclopentadiene and the η1-2-phenylethanethial complex.

Ｄｉｅｌｓ‐Ａｌｄｅｒ反応におけるπ面選択性と発現機構

Controlling of the π-facial stereoselectivity in Diels-Alder reactions has been one of the most fundamental and attractive subjects of theoretical and experimental studies.Increasing attention has been focused on the selectivity in the reaction of 5-substituted cyclopentadienes, the simplest diene having unsymmetrical π-plane. The, π-facial selectivity is highly dependent on the substituents 1) The diene having 5-alkyl or 5-trimethylsilyl group reacted with dienophiles with anti-π-facial selectivity; 2) 5-Hydroxy, 5-acetoxy, or 5-fluoro moiety leads to the opposite stereochemical results. The former case is simply attributable to the steric repulsion between the substituents and dienophiles. However, the origin of the syn selectivity in the latter case has been the subject of intensive studies.The present paper describes a short review on the theories developed for the prediction and explanation of the π-facial selectivity in the Diels-Alder reactions of these simple dienes.

2-(penta-1,3-dienyl)oxazolidines: synthesis of hydroxylated piperidines by a stereoselective diels-alder Reaction

Hexa-2,4-dienal condensed with (-)-ephedrine to give predominantly the oxazolidine 4, which underwent a stereoselective Diels-Alder reaction with benzyl nitrosoformate to give the cycloadducts 9 and 10 in a ca 5:2 ratio. Further transformations of 9 to give the optically active mono- and tri- hydroxypiperidine derivatives 11 and 15 have also been performed.

Cycloaddition reactions of λ-amino α,β-didehydro amino acid esters: a test case for the principle of 1,3-allylic strain

N,N-Dibenzlamino aldehydes, readily accessible from amino acids, can be converted into λ-N,N-dibenzylamino α,β-didehydro amino acid esters without racemization; these undergo stereoselective Diels-Alder reactions and 1,3-dipolar cycloaddition with diazomethane, the sense of diastereoselectivity being opposite to that predicted by the conventional principle of 1,3-allylic strain.

Highly regio- and stereo-selective Diels–Alder reactions of 5-(2′,3′,4′,6′-tetra-O-acetyl-β-D-glucopyranosyloxy)-1,4-naphthoquinone

The title compound 1b reacts with cyclopentadiene to give a single cycloadduct, assigned the stereostructure 6a by X-ray crystallography; single cycloadducts, i.e.4c and d, also arise in the corresponding reactions involving the dienes 2b and c.