Intramolecular Chromium(II)-Catalyzed Pinacol Cross Coupling of 2-Methylene-α,ω-dicarbonyls

Groth, Ulrich; Jung, Marc; Vogel, Till

doi:10.1055/s-2004-822895

Cited by 22 publications

(16 citation statements)

References 5 publications

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“…In the intramolecular case, we chose 2-methylene-1,6-hexanedialdehyde (3) as a precursor for the cyclization because of its relatively poor cis/trans-selectivity with the usually used scavenger TMS-Cl. 4 As expected, depending on the nature of the silylating agent, trans or cis selectivity was observed. Table 1 shows the remarkable influence of the silylating reagent on the diastereoselectivity.…”

supporting

confidence: 67%

“…4 In this case, the diastereoselectivities are mainly dependent on ring sizes and the substitution of the x-carbonyl group.…”

mentioning

confidence: 99%

“…After additional 4 h of stirring at an ambient temperature, ether (20 ml) and water (20 ml) were added. After separation of the organic layer, the aqueous layer was extracted with ether (3 · 20 ml), the combined organic layers were dried over MgSO 4 and concentrated in vacuo. THF (10 ml) and TBAF (1.4 g, 4 mmol) were added to the residue and the mixture was stirred for 45 min at room temperature.…”

mentioning

confidence: 99%

“…THF (10 ml) and TBAF (1.4 g, 4 mmol) were added to the residue and the mixture was stirred for 45 min at room temperature. After adding water (10 ml) and ether (20 ml), the aqueous layer was extracted with ether (4 · 20 ml), the combined organic layers were dried over MgSO 4 and concentrated in vacuo. The residue was purified by flash chromatography on 40 g of silica gel (petrol ether/ethyl acetate 4:1 to 1:1).…”

mentioning

confidence: 99%

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Influence of chelating silyl scavengers on the diastereoselectivity of chromium catalyzed pinacol cross couplings

Fischer

Groth

Jung

et al. 2005

Tetrahedron Letters

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Abstract-The choice of the silyl scavenger shows a substantial influence on the diastereoselectivity of the chromium catalyzed pinacol cross coupling. In the case of the intramolecular cyclization, two competing effects are observed. If the silylation reagents contain chelating heteroatoms in the side chain, a remarkable trans-selectivity is observed. Conversely the cis-diols are preferred if bulky substituted scavengers are used. A suitable transition state model for this reaction is reported, based on formerly published results. Ó 2005 Elsevier Ltd. All rights reserved.Recently, we have reported a chromium catalyzed diastereoselective pinacol cross coupling.2 It was found that the diastereoselectivities of the coupling reactions are mainly substrate dependent (Scheme 1).3 Furthermore, we have reported an intramolecular cyclization of 2-methylene-a,x-dicarbonyl compounds by chromium catalyzed pinacol cross coupling. 4 In this case, the diastereoselectivities are mainly dependent on ring sizes and the substitution of the x-carbonyl group.The starting point of our catalytic cross coupling reaction of acroleins with aldehydes was a publication by Takai and co-workers reporting a chromium-mediated process using a high excess of chromium(II) chloride to couple vinylketones with various aldehydes.5 Takai described that changing the silyl scavenging reagent only had little effect on diastereoselectivities under his reaction conditions.Encouraged by former results dealing with the effect of different scavenger reagents in the homo pinacol coupling, 6 we tried to substitute our scavenging trimethylsilyl chloride (TMS-Cl) with acetyl chloride, which we thought to be suitable to liberate chromium(III) chloride from the intermediate chromium alcoholate. 7 We found that the reaction was no longer catalytic in chromium or proceeded very slow albeit with a dramatic increase in diastereoselectivity (coupling of ethyl acrolein with 3-phenylpropionic aldehyde: 23% de, syn, with TMS-Cl, 78% yield; 54% de, syn, with AcCl, 10% yield).Maintaining the apparently positive chelating effect in the side chain of the scavenger, we switched back to silyl chlorides of the type ROMe 2 Si-Cl.8 Although diastereoselectivities were not as high as in the case of acetyl chloride, a significant increase, compared to TMS-Cl, could be observed (50% de, syn, 83% yield).

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supporting

confidence: 67%

“…4 In this case, the diastereoselectivities are mainly dependent on ring sizes and the substitution of the x-carbonyl group.…”

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Influence of chelating silyl scavengers on the diastereoselectivity of chromium catalyzed pinacol cross couplings

Fischer

Groth

Jung

et al. 2005

Tetrahedron Letters

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“…An intramolecular version of the described chromium-catalyzed pinacol cross-coupling reaction serving as a method for the formation of small and mid-sized rings has been reported by us recently. [16] Results and Discussion…”

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confidence: 99%

Chromium‐Catalyzed Pinacol‐Type Cross‐Coupling: Studies on Stereoselectivity

Groth¹,

Jung²,

Vogel³

2005

Chemistry A European J

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A chromium‐catalyzed pinacol‐type cross‐coupling reaction between α,β‐unsaturated carbonyl compounds and aldehydes is reported. Even sterically demanding substrates could be coupled to afford the corresponding pinacols in good yields. Systematic studies concerning the origin of the diastereoselectivities led to the proposal of a mechanism for this synthetically useful reaction. Acroleins with α‐branched alkyl side chains were coupled to give the corresponding syn pinacols, while on the other hand, acroleins with less bulky substituents furnished the anti derivatives. The effects of both the substrates and the reagents on the diastereo‐ and enantioselectivities were investigated. An unexpected catalytic formation of cyclopropanols was found.

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N‐Heterocyclic Carbene‐Mediated Organocatalytic Transfer of Tin onto Aldehydes: An Easy Access to syn‐Diols and Mechanistic Studies

et al. 2012

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An update of our preliminary communication concerning an efficient organocatalytic procedure for the transfer of tin onto aldehydes is presented. This update combines (i) a full study of the preparation of γ‐silyloxyallylstannanes from β‐substituted enals, (ii) a “one‐pot” sequence (in inter‐ and intramolecular version) including N‐heterocyclic carbene (NHC)‐catalyzed silylstannation reaction/Lewis acid‐promoted allylstannation reaction to furnish the corresponding syn‐diols, and (iii) mechanistic studies on the organocatalytic 1,2‐addition.

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Intramolecular Chromium(II)-Catalyzed Pinacol Cross Coupling of 2-Methylene-α,ω-dicarbonyls

Cited by 22 publications

References 5 publications

Influence of chelating silyl scavengers on the diastereoselectivity of chromium catalyzed pinacol cross couplings

Influence of chelating silyl scavengers on the diastereoselectivity of chromium catalyzed pinacol cross couplings

Chromium‐Catalyzed Pinacol‐Type Cross‐Coupling: Studies on Stereoselectivity

N‐Heterocyclic Carbene‐Mediated Organocatalytic Transfer of Tin onto Aldehydes: An Easy Access to syn‐Diols and Mechanistic Studies

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