Alkyne Hydroacylation: Switching Regioselectivity by Tandem Ruthenium Catalysis

The hydroamination of internal alkynes via tandem rhodium-catalysis gives branched N-allylic indolines with high regio- and enantioselectivity. An acid-switch provides access to the linear isomer in preference to the branched isomer by an isomerization mechanism. Mechanistic studies suggest formation of an allene intermediate, which undergoes hydroamination to generate allylic amines instead of the enamine or imine products typically observed in alkyne hydroaminations.

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“…Using alkynes as allene surrogates can enable transformations that would be sluggish with allene precursors. 6a,7 …”

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confidence: 99%

Rhodium-Catalyzed Enantioselective Hydroamination of Alkynes with Indolines

2015

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“…This study contributes to our emerging interest in using tandem catalysis to address challenges in organic synthesis, including tandem Ru-catalyzed hydroacylations 27,28 and tandem Ru-catalyzed aminations. 29 The first demonstration of a catalytic asymmetric transformation of racemic allylic sulfoxides is achieved through Rh-catalyzed hydrogenation.…”

Section: Conclusion and Future Outlookmentioning

confidence: 94%

Tandem rhodium catalysis: exploiting sulfoxides for asymmetric transition-metal catalysis

Kou

Dong

2015

Org. Biomol. Chem.

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Sulfoxides are uncommon substrates for transition-metal catalysis due to their propensity to inhibit catalyst turnover. In a collaborative effort with Ken Houk, we developed the first dynamic kinetic resolution (DKR) of allylic sulfoxides using asymmetric rhodium-catalyzed hydrogenation. Detailed mechanistic analysis of this transformation using both experimental and theoretical methods revealed rhodium to be a tandem catalyst that promoted both hydrogenation of the alkene and racemization of the allylic sulfoxide. Using a combination of deuterium labelling and DFT studies, a novel mode of allylic sulfoxide racemization via a Rh(III)-π-allyl intermediate was identified.

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“…[9,17,18] Applying the commercially available (R)-DTBM-Garphos as ap rivileged ligand, ac lean allylic etherification of phenylmethyl alkyne could be observed, thus furnishing the allylic ether 5a in 63 %y ield and with 89 % ee (Table 3). [9,17,18] Applying the commercially available (R)-DTBM-Garphos as ap rivileged ligand, ac lean allylic etherification of phenylmethyl alkyne could be observed, thus furnishing the allylic ether 5a in 63 %y ield and with 89 % ee (Table 3).…”

Section: Zuschriftenmentioning

confidence: 99%

Rhodium‐Catalyzed Enantioselective Intermolecular Hydroalkoxylation of Allenes and Alkynes with Alcohols: Synthesis of Branched Allylic Ethers

Breit

2016

Angewandte Chemie

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Regio-and enantioselective additions of alcohols to either terminal allenes or internal alkynes provides access to allylic ethers by using a Rh I /diphenyl phosphate catalytic system. This method provides an atom-economic way to obtain chiral aliphatic and aryl allylic ethers in moderate to good yield with good to excellent enantioselectivities.Allylic ethers are key components of bioactive molecules and natural products and serve as versatile synthetic intermediates for further construction of numerous structures [1] through a wide variety of reactions such as [2,3] and [3,3] sigmatropic rearrangements and olefin metathesis reactions, among many others.[1b, 2, 3] Significant progress towards their synthesis has been achieved recently by employing transition metal catalyzed allylic substitution. In most cases, allyl acetates [4] or carbonates [5] have been used as electrophiles. However, recent studies show that even allylic alcohols can serve as allyl precursors.[6] To date, premetalated alkoxides have been used as nucleophiles along with metals to soften the hard nucleophilic character of an alkoxide (such as tin, [4a] boron, [7] zinc, [4b,c, 5f] and copper [5a,c-e] ). Following on the initial work with palladium catalysts of the groups of Trost [8] and Yamamoto, [9] we recently reported on a series of rhodium-catalyzed pronucleophile addition reactions to allenes and alkynes, reactions that can be regarded as atom-economic alternatives to allylic substitution chemistry displaying complementary branch regioselectivity (Scheme 1). [10] Thus, hydroamination, [11] hydroesterification, [12] hydroacylation, [13] and hydrothiolation [14] have been achieved to afford versatile enantioenriched branched allylic products. In this context, it would be highly interesting if simple and non-deprotonated alcohols could be added atom economically to allenes or even to alkynes, thus giving valuable branched allylic ether products.We herein report on the implementation of such a transformation allowing the highly regio-and enantioselective addition of simple and functionalized alcohols, including methanol and ethanol, to terminal allenes and internal alkynes to give a wide range of valuable building blocks for synthetic organic chemistry.Initial reactions were conducted with 3-phenylpropyl allene (1 a) and ethanol (2 b) as model substrates. First reactivity assays indicated that the presence of an acidic cocatalyst was necessary. The reaction proved to work using a rhodium(I)/DPEphos/diphenyl phosphate catalyst in dichloromethane (DCM) at 40 8C for 18 hours and furnished the desired allylic ether in 34 % yield (Table 1, entry 1). [15] Inspired by this result, various chiral bidentate diphosphine ligands with different backbones were subjected to this model reaction. While many standard privileged chiral ligands failed to catalyze this reaction, [16] the chiral ferrocene-type ligand L4 proved to be the best (entries 5 and 6). To our delight, switching the solvent from DCM to 1,2-dichloroethane (DCE) gave th...

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Alkyne Hydroacylation: Switching Regioselectivity by Tandem Ruthenium Catalysis

Cited by 85 publications

References 75 publications

Rhodium-Catalyzed Enantioselective Hydroamination of Alkynes with Indolines

Rhodium-Catalyzed Enantioselective Hydroamination of Alkynes with Indolines

Tandem rhodium catalysis: exploiting sulfoxides for asymmetric transition-metal catalysis

Rhodium‐Catalyzed Enantioselective Intermolecular Hydroalkoxylation of Allenes and Alkynes with Alcohols: Synthesis of Branched Allylic Ethers

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