1,2-Asymmetric Induction in the Conjugate Addition of Organocopper Reagents to γ-Aryl α,β-Unsaturated Carbonyl Derivatives

Chounan, Yukiyasu; Ono, Yoshio; Nishii, S.; Kitahara, Haruo; Ito, Shoei; Yamamoto, Yoshinori

doi:10.1016/s0040-4020(00)00137-x

Cited by 21 publications

(10 citation statements)

References 33 publications

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“…A good analogy for this process would be the conjugate additions of organometallics and other nucleophiles to acyclic γ-chiral α,β-unsaturated esters, which have been extensively studied both experimentally and theoretically . For example, with ( E )-α,β-unsaturated esters having γ-substituents as in 4 , the reaction usually proceeds via a transition state similar to that in Figure and therefore the major addition product is anti (with the corresponding ( Z )-isomer, syn is usually preferred).…”

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Investigation of the Stereochemistry of Intermolecular Conjugate Additions of Nucleophiles to Acyclic Nitrosoalkenes

Witek

Weinreb

2011

Org. Lett.

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Michael-type conjugate additions of γ-chiral aldehyde-derived acyclic nitrosoalkenes have been explored using a series of carbon and hetero nucleophiles. In all cases examined, these reactions are stereoselective, leading exclusively to the anti products.Vinylnitroso compounds 1 are highly reactive, short-lived species which have found only sporadic use in organic synthesis. 1 To date, very few of these intermediates have actually been isolated and characterized, and they are usually generated and trapped in situ. One potentially valuable reaction of nitrosoalkenes involves intermolecular conjugate additions of hetero and carbon nucleophiles in a Michael-type of transformation to produce adducts such as 2 (eq 1). By this process nitrosoalkenes 1 can act as enolonium ion equivalents, thereby allowing a simple method for the umpolung of the usual enolate reactivity. 2 However, these vinylnitroso species have been the object of surprisingly little systematic study and have not seen application to the synthesis of complex molecules. We have recently been exploring the scope of both inter-3 and intramolecular 4 conjugate additions of these reactive intermediates with a variety of nucleophiles. Recently, we have also begun to investigate various stereochemical issues relevant to these reactions which have never been addressed, and some of this work is the subject of this communication. Our initial studies were designed to probe the stereoselectivity of conjugate additions of acyclic aldehyde-derived nitrosoalkenes bearing a γ-stereogenic center (Cf 4, Scheme 1). It should also be noted that relatively few examples exist in the literature of reactions of nitrosoalkenes generated from aldehydes. 3,5 For this work, we have opted to generate the requisite nitrosoalkene by the Denmark method, which involves exposure of an O-TBS-α-chlorooxime to a fluoride source.6 Therefore, known α-chloro-γ-methyldihydrocinnamaldehyde 7 (racemic, mixture of diastereomers) was converted to O-TBS-oxime 3 with commercially available O-TBS-hydroxylamine (see Supporting Information). Conjugate additions to the vinylnitroso compound derived from 3 were then effected with a series of four malonate anions as the nucleophiles (Scheme 1). Thus, the malonate (2 equiv) was first deprotonated with potassium hexamethyldisilazide in THF at low temperature followed by addition of O-silyloxime 3 (1 equiv). Tetrabutylammonium fluoride (2 equiv) in THF was then added at −78 °C and the mixture was warmed to 0 °C to generate the nitrosoalkene 4. We were pleased to find that in each case the malonate enolate addition was completely stereoselective, producing only the anti stereoisomeric adducts 5-8. Oximes 7 and 8 appear to be single geometric isomers assumed to be (E), whereas 5 and 6 are ~9-10:1 (E/Z) mixtures. 8,9 In order to establish the configuration of these adducts, α-allylmalonate oxime 5 was heated in toluene at 190 °C (sealed tube) to generate nitrone 9, which then cyclizes via the conformation shown to afford cis-fused bicyclic isoxazolidin...

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Investigation of the Stereochemistry of Intermolecular Conjugate Additions of Nucleophiles to Acyclic Nitrosoalkenes

Witek

Weinreb

2011

Org. Lett.

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“…g-Aryl a,b-unsaturated carbonyl compounds are useful building blocks because they can be further functionalized at the carbonyl or olefinic positions. [2] To develop a catalyst for the g-arylation of a,b-unsaturated carbonyl compounds, one must address several issues, including the regioselectivity for forming products from a-, b-, or g-arylation, the selectivity for monoarylation versus diarylation, and the potential condensation of the reactive products. The selectivity for formation of products from aor g-arylation versus b-arylation depends on whether an enolate complex forms by transmetalation with the arylpalladium halide intermediate, as occurs during the a-arylation of carbonyl compounds, or whether it forms by insertion of the a,b-unsaturated carbonyl compound into the metal-aryl bond, as occurs during a Heck reaction.…”

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Palladium‐Catalyzed γ‐Arylation of α,β‐Unsaturated Esters from Silyl Ketene Acetals

Huang

Hartwig

2010

Angewandte Chemie

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The palladium-catalyzed coupling of enolates with aryl and vinyl electrophiles has become a useful method for the construction of carbon-carbon bonds.[1] Although many palladium complexes have been identified that catalyze the coupling of enolates of ketones, esters, amides, and aldehydes with haloarenes, the vinylogous coupling of dienolates of a,bunsaturated carbonyl compounds with haloarenes (g-arylation) has been less studied. g-Aryl a,b-unsaturated carbonyl compounds are useful building blocks because they can be further functionalized at the carbonyl or olefinic positions. [2] To develop a catalyst for the g-arylation of a,b-unsaturated carbonyl compounds, one must address several issues, including the regioselectivity for forming products from a-, b-, or g-arylation, the selectivity for monoarylation versus diarylation, and the potential condensation of the reactive products. The selectivity for formation of products from aor g-arylation versus b-arylation depends on whether an enolate complex forms by transmetalation with the arylpalladium halide intermediate, as occurs during the a-arylation of carbonyl compounds, or whether it forms by insertion of the a,b-unsaturated carbonyl compound into the metal-aryl bond, as occurs during a Heck reaction. The selectivity for products from a-versus g-arylation likely depends on the stability and reactivity of the series of isomeric arylpalladium dienolate intermediates that result from transmetalation.Despite these obstacles, a few g-arylation reactions of a,bunsaturated ketones and aldehydes have been reported. Terao et al. reported the palladium-catalyzed g-arylation of unfuntionalized a,b-unsaturated aldehydes and ketones. [3] Martin and Buchwald reported the g-arylation of similar asubstituted a,b-unsaturated aldehydes.[4] Varseev and Maier later reported a sequential g-arylation and dehydrogenation for the synthesis of substituted tetralones.[5] Finally, Hyde and Buchwald reported the g-arylation of g-substituted a,b-or b,g-unsaturated ketones [6] and lactones [7] with aryl chlorides and bromides in moderate to good yield.Despite these advances, the coupling of enolates of a,bunsaturated esters is underdeveloped. The g-arylation of acyclic esters has been limited to reactions of tin enolates in low to moderate yields.[8] Moreover, the previous couplings of a,b-unsaturated ketones and aldehydes have required elevated temperatures and substrates that contain substituents at either the a or g position of the carbonyl compound for high yield.Herein, we report the g-arylation and g-vinylation of a,bunsaturated esters in high yield with broad scope by coupling aryl, heteroaryl, and vinyl halides with the corresponding silicon dienolates. These reactions occur in high yield with a variety of esters, including those lacking substituents at the a and g positions, and with aromatic and vinylic electrophiles that contain potentially reactive functional groups. Moreover, these reactions occur without typical fluoride additives to activate silicon enolates.Our studies of t...

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“…1 H NMR of product 4d 2-nitro-4-phenyl-2-pentene, 4e:5 The product 4e was isolated as a pale-yellow solid in a 67% yield (0.19 g) 1. H NMR (CDCl 3 ) : 7.36-7.22 (m, 6H), 3.71 (dq, 1H, J = 6.9 Hz, J' = 10.3 Hz), 2.23 (d, 3H, J H-H =1.0 Hz), 1.47 (d, 3H, J H-H = 6.9 Hz).…”

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Selective Nitroaldol Condensations over Heterogeneous Catalysts in the Presence of Supercritical Carbon Dioxide

et al. 2008

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At 40-60 degrees C, in the presence of heterogeneous catalysts based on Al2O3, supercritical carbon dioxide not only acts as a good solvent for the reaction of aromatic and aliphatic aldehydes with 1-nitroalkanes but, most importantly, it also allows the selectivity to be tuned between the competitive formation of beta-nitroalcohols and nitroalkenes (from the Henry reaction and the nitroaldol condensation, respectively). In particular, when the pressure (and the density) of the supercritical phase is enhanced from 80 to 140 bar, the nitroalkene's selectivity increases, on average, from approximately 60 to >90%. Experiments show that, in the same pressure range, a steep increase of the concentration profiles of reactant aldehydes takes place. By contrast, under solvent-free conditions, the reaction usually proceeds with a higher conversion, but nitroalkanols are the major products.

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1,2-Asymmetric Induction in the Conjugate Addition of Organocopper Reagents to γ-Aryl α,β-Unsaturated Carbonyl Derivatives

Cited by 21 publications

References 33 publications

Investigation of the Stereochemistry of Intermolecular Conjugate Additions of Nucleophiles to Acyclic Nitrosoalkenes

Investigation of the Stereochemistry of Intermolecular Conjugate Additions of Nucleophiles to Acyclic Nitrosoalkenes

Palladium‐Catalyzed γ‐Arylation of α,β‐Unsaturated Esters from Silyl Ketene Acetals

Selective Nitroaldol Condensations over Heterogeneous Catalysts in the Presence of Supercritical Carbon Dioxide

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