Homogeneous catalysis. Catalytic production of simple enols

Bergens, Steven H.; Bosnich, B.

doi:10.1021/ja00003a032

Cited by 175 publications

(71 citation statements)

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“…Instead, 5 and 8 were obtained in 75 %and 93 %yield, respectively.T he results of these experiments are in good agreement with the intramolecular addition of an acylhydridorhodium intermediate and the endocyclic b-H elimination envisioned in Figure 1. In contrast to many precedents,n either the reversible intermolecular addition of am etal-hydride species [14] nor allylic CÀHa ctivation [15] can account for the olefin isomerization examined herein.…”

contrasting

confidence: 77%

Isomerization of Olefins Triggered by Rhodium‐Catalyzed CH Bond Activation: Control of Endocyclic β‐Hydrogen Elimination

Yip

Aïssa

2015

Angewandte Chemie

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Five-membered metallacycles are typically reluctant to undergo endocyclic b-hydrogen elimination. The rhodiumcatalyzedisomerization of 4-pentenals into 3-pentenals occurs through this elementary step and cleavage of two CÀHbonds, as supported by deuterium-labeling studies.T he reaction proceeds without decarbonylation, leads to trans olefins exclusively,a nd tolerates other olefins normally prone to isomerization. Endocyclic b-hydrogen elimination can also be controlled in an enantiodivergent reaction on ar acemic mixture.Five-membered metallacycles are important intermediates of numerous catalytic processes,b oth in academic laboratories and in large-scale industrial chemistry.[1] As shown in experimental [2] and theoretical [3] studies,g eometric constraints make these intermediates reluctant to undergo endocyclic b-hydrogen (b-H) elimination, especially in the case of square-planar complexes.H owever,a nd although thorough experimental studies are still lacking, theoretical studies suggest that five-membered metallacycles that are not square-planar could undergo b-H elimination more easily. [5] Importantly,s ubstrate decarbonylation is anotorious problem during the hydroacylation of 4-pentenals, especially in the case of a,a-disubstituted aldehydes (R ¼ 6 H). [6][7][8][9] In contrast, we have found that the rhodium-catalyzed isomerization of 4-pentenal 1 (R = Ph) into 3-pentenal 2 occurs without decarbonylation in 86 %yield and in ahighly stereoselective fashion. Them ost efficient catalyst was prepared with ligand L1, [10] whereas those prepared with L2-L5 led to incomplete conversion and decarbonylation. Hence,weassumed this isomerization to be triggered by C À H bond activation (a), and the catalytic cycle would be completed by migratory insertion of the terminal olefin into the rhodium-hydrogen bond thus engendered (b), followed by endocyclic b-H elimination of A (R = Ph) (c), and final reductive elimination (d).Herein, we report at horough study of the reaction depicted in Figure 1, including deuterium-labeling experiments that support the postulated mechanism and the endocyclic b-H elimination of rhodacyclopentanone A. Moreover,w ea lso show that the isomerization is chemoselective for olefins that enable the formation of A,a nd that olefins located elsewhere on the substrate remain intact under the reaction conditions,e ven in the challenging case of sensitive olefins normally prone to facile isomerization in the presence of transition-metal catalysts, [11] including rhodium catalysts.[12] Finally,w ed escribe how the endocyclic b-H elimination of rhodacyclopentanones can be prevented, whereby each enantiomer of the racemic 4-pentenal undergoes ad istinct and enantioselective rearrangement when treated with an enantiopure catalyst.We found that the rhodium-catalyzed isomerization of deuterated substrates 3 and 4 into compounds 5 and 6, respectively,occurred smoothly with complete transfer of the deuterium atom at the positions indicated in Scheme 1. Tr ansient intermediate 3-int was observed ...

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confidence: 77%

Isomerization of Olefins Triggered by Rhodium‐Catalyzed CH Bond Activation: Control of Endocyclic β‐Hydrogen Elimination

Yip

Aïssa

2015

Angewandte Chemie

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“…En01 15 has previously been described in pioneering work by Hoffmann and Schmidt (7), and a comparison of 'H NMR data (6 4.77 and 4.92 in CCI, solvent) indicates a close fit. Furthermore, in en01 16, the proton on the en01 double bond is assigned to a quartet at 6 4.02, very similar in chemical shift to that reported (8) For personal use only. chemical shift positions also agree well with those reported (7).…”

Section: Resultssupporting

confidence: 74%

“…Fronz presumed cycloproparzone 8 The reactions were carried out in the standard way except that a four-fold excess of either cyclopentadiene or furan was mixed with the CH,CI, solvent used to dissolve the chromium salt. The cyclopentadiene adduct has been reported (19) …”

Section: Fur-c~n and Cyclopenrndiene Trapping Reactionsmentioning

confidence: 99%

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A new synthesis of in situ cyclopropanones and the observation of a thermal cyclopropanone–dienol rearrangement

Black¹,

Lario²,

Masters³

et al. 1993

Can. J. Chem.

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A new in situ low-temperature synthesis of cyclopropanones from cu,cul-dibromo ketones is described. The synthetic procedure is particularly well suited to NMR tube-scale experiments, which then easily allows one to spectroscopically characterize low-temperature solutions of these unstable molecules. Nine systems were studied, seven of which give high yields of the cyclopropanones at -78OC or, in one case, -93°C. ' The major rearrangement pathway of these cyclopropanones leads to an a,P-unsaturated ketone. The mechanism of this reaction has been studied in some detail, including deuterium isotope studies, and the direct observation of enols, silyl enol ethers, and dimers. The rearrangement reaction is postulated to involve the intermediacy of an oxyallyl, the transfer of a hydrogen from the anti-alkyl substituent of this oxyallyl to the oxyallyl oxygen atom, which leads to an enol, and then finally tautomerization of the en01 to the ketone. The thermal stability of the cyclopropanones is directly related to the ease of this rearrangement and, in two cases studied here, the rearrangement takes place rapidly even at -95°C and the cyclopropanones could not be observed. There is a remarkably strong correlation between cyclopropanone structure and reactivity, with the main structural factor being the external angles of the cyclopropanone substituents.C. BLACK, P. LARIO, A.P. MASTERS, T.S. SORENSEN et F. SUN. Can. J. Chem. 71, 1910 (1993. On dCcrit une nouvelle synthkse in situ et a basse temptrature des cyclopropanones a partir d1cu,a'-dibromocttones. La mkthode de synthkse est particuliitrement adaptCe a des etudes dans des tubes de RMN; cette particularit6 permet d'obtenir facilement une caracterisation spectroscopique basse temperature de solutions de ces espkces instables. On a Ctudit neuf systitmes, dont sept qui donne d'excellents rendements en cyclopropanones 2 -78°C ou, dans un cas, 2 -93°C. La voie reactionnelle du rkarrangement principal de ces cyclopropanones conduit a une cCtone a,P-insaturee.On a CtudiC en dCtail le mCcanisme de cette reaction, incluant des ttudes d'effet isotopique du deuterium ainsi que l'observation directe d'enols, d'kthers Cnoliques silylCs et de dimeres. On suggkre que la reaction de rkarrangement implique un oxyallyle comme intermkdiaire, le transfert d'un hydrogitne a partie du substituant alkyle anti de cet oxyallyle vers l'atome d'oxygbne de l'oxyallyle, qui conduit a un Cnol, et finalernent une tautomCrisation de I'Cnol en cktone. La stabilitk thermique des cyclopropanones est directement reliee a la facilite de ce rearrangement et, dans deux cas CtudiCs ici, ce rearrangement se produit tellement rapidement m2me a -95°C que les cyclopropanones n'ont pu &tre observees.I1 existe une forte corrtlation importante entre la structure de la cyclopropanone et la reactivit6, le facteur structural principal etant les angles externes des substituants de la cyclopropanone.[Traduit par la rkdaction]Turro and co-workers pioneered the first preparations (as in situ solution species) of sever...

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“…an h 1 -C rhodium species III, [10f] which is anticipated to be in equilibrium with an oxa-p-allyl species [15] or h 1 -O rhodium enolate. [16] The presence of a coordinating functionality in the substrate at the b position induces competition between cyclization and elimination pathways. The combination of an NMe linker and a diphosphine ligand results in cyclization to afford 7, presumably via the h 1 -O haptomer.…”

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confidence: 99%

Catalytic Enantioselective Dieckmann‐Type Annulation: Synthesis of Pyrrolidines with Quaternary Stereogenic Centers

et al. 2010

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Homogeneous catalysis. Catalytic production of simple enols

Cited by 175 publications

References 3 publications

Isomerization of Olefins Triggered by Rhodium‐Catalyzed CH Bond Activation: Control of Endocyclic β‐Hydrogen Elimination

Isomerization of Olefins Triggered by Rhodium‐Catalyzed CH Bond Activation: Control of Endocyclic β‐Hydrogen Elimination

A new synthesis of in situ cyclopropanones and the observation of a thermal cyclopropanone–dienol rearrangement

Catalytic Enantioselective Dieckmann‐Type Annulation: Synthesis of Pyrrolidines with Quaternary Stereogenic Centers

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