In Situ Generation of Nucleophilic Allenes by the Gold‐Catalyzed Rearrangement of Propargylic Esters for the Highly Diastereoselective Formation of Intermolecular C(sp3)C(sp2) Bonds

Yu, Yang; Yang, Weibo; Röminger, Frank; Hashmi, A. Stephen K.

doi:10.1002/anie.201302402

Cited by 95 publications

(45 citation statements)

References 72 publications

(9 reference statements)

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“…Multiplicity is indicated by one or more of the following: s (singlet); d (doublet); t (triplet); q (quartet); sep (septet); m (multiplet); br (broad). Carbon nuclear magnetic resonance ( Preperation of Propargyl Esters 3-Phenylprop-2-yn-1-yl Pivalate (11a) 42) To the solution of 3-phenyl-2-propyn-1-ol (1.32 g, 10.0 mmol), NEt 3 (7.0 mL, 50.0 mmol) and 4-(dimethylamino)pyridine (DMAP) (127.5 mg, 1.05 mmol) in methylene chloride (CH 2 Cl 2 ) (50 mL) at 0°C was added pivaloyl chloride (1.35 mL, 11.0 mmol) slowly under Ar and the mixure was warmed to room temperature. After stirring for 2 h, the mixture was quenched with water and extracted with chloroform (CHCl 3 149.7, 134.9, 132.8, 129.0, 124.6, 117.7, 91.4, 81.3, 52.6 The reaction was performed according to the procedure for 45) The reaction was performed according to the procedure for 11a.…”

Section: Methodsmentioning

confidence: 99%

Synthesis of α-Acyloxyketone Derivatives via the Platinum-Catalyzed Migration of Propargylic Esters

Tsukano

Yamamoto

Takemoto

2015

CHEMICAL & PHARMACEUTICAL BULLETIN

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The synthesis of α-acyloxyketones via the migration of a propargylic ester followed by the intramolecular nucleophilic addition of the resulting allene was achieved using a cationic platinum catalyst. The optimized conditions for this transformation were determined to be 3 mol% of Pt(cod)Cl 2 , 3 mol% of AgNTf 2 , and 3 eq of water in toluene at 100°C, and these conditions were successfully applied to the synthesis of a wide variety of α-aryl-α-acyloxyketones. The mechanism of this reaction was evaluated in detail based on the results of isotope labeling experiments using H 2 18 O.Key words platinum; propargylic ester migration; α-acyloxyketone α-Acyloxyketone, which is a protected form of α-hydroxyketone, is a fundamental structure that can be found in a broad range of natural products and bioactive compounds, including hainanmurpanin, 1) paniculatin 2) and murpaniculol senecioate 3) (Fig. 1). α-Acyloxyketone has also been used as a simple starting material for the stereoselective synthesis of a variety of different structures, including numerous 1,2-diols 4-8) and heterocyclic systems.9-11) Based on the importance of α-acyloxyketones to chemistry, the development of a concise synthetic method for the preparation of α-acyloxyketone derivatives is important. Although a wide variety of synthetic methods have been investigated to date, 12,13) reports pertaining to the direct synthesis of α-acyloxyketone III by the oxidation of alkyne I are rare, most likely because of the difficulties associated with suppressing the over-oxidation of the product and controlling the regioselectivity of the reaction 14-16) (Chart 1). To allow for the direct synthesis of α-acyloxyketone III from alkyne I, several researchers directed their attention towards the transition metal-catalyzed migration of propargylic esters [17][18][19][20] to affect a facile oxidative transformation. [21][22][23][24][25][26][27][28][29][30] For example, in 1991, Schick and Mahrwald 21) reported that the treatment of propargyl acetate 1 with PdCl 2 (MeCN) 2 gave a 1 : 1 mixture of α-acyloxyketone 2 and α,β-unsaturated ketone 3 via the rearrangement of the acetyl group (Chart 2(a)). Ohfune et al. 24)also reported the synthesis of α-acyloxy-α′-siloxyketone 4 using a gold catalyst (Chart 2(b)). Under Ohfune's conditions, it was observed that substrates without a silyl group did not undergo the reaction, and it was therefore assumed that the silyl group was essential for stabilizing the β cation of reaction intermediate 5 (or 6). Although these reactions provided facile access to the α-acyloxyketones 2 and 4 from the readily accessible propargyl esters 1 and 3, several opportunities still remained to improve on this reaction in terms of the selectivity and substrate scope. For improving the scope of this reaction, we focused on enhancing the π-acidity of the transition metal catalyst (i.e., palladium, gold or platinum catalyst) by decreasing its electron density. [17][18][19][20] If allene 9, which was derived from 7, could be strongly activated by a π-a...

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Section: Methodsmentioning

confidence: 99%

Synthesis of α-Acyloxyketone Derivatives via the Platinum-Catalyzed Migration of Propargylic Esters

Tsukano

Yamamoto

Takemoto

2015

CHEMICAL & PHARMACEUTICAL BULLETIN

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“…[9] Moreover,t ov alidate the chemical sustainability of this method, we selected environmentally desirable allylic alcohols [10] as potential alkylating agents (Scheme 2). Allenamides have already been used in numerous elegant applications in gold catalysis;however,most often the condensation of nucleophilic species with the metal-activated allenyl unit is the dominant chemical event in these transformations.…”

Section: And [H +mentioning

confidence: 99%

Gold(I)‐Assisted α‐Allylation of Enals and Enones with Alcohols

et al. 2015

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The intermolecular α-allylation of enals and enones occurs by the condensation of variously substituted allenamides with allylic alcohols. Cooperative catalysis by [Au(ItBu)NTf2] and AgNTf2 enables the synthesis of a range of densely functionalized α-allylated enals, enones, and acyl silanes in good yield under mild reaction conditions. DFT calculations support the role of an α-gold(I) enal/enone as the active nucleophilic species.

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“…Upon gold(I)/gold(III) transmetalation followed by reductive elimination, the new Csp 2 −Csp 2 bond is formed. Recently, Hashmi and coworkers have reported an intermolecular Csp 3 −Csp 2 bond formation in which the nucleophilic allene generated from 47 reacts with an electrophilic oxocarbenium ion generated in situ from a cyclic acetal introduced in the reaction mixture (Scheme 23) 54 . The diastereoselectivities are good to excellent, obtaining in some cases only the Z isomer.…”

Section: 3-ester Migration Of Propargyl Estersmentioning

confidence: 99%

Gold‐Catalyzed Migrations and Ring Expansions

Merino

Fernández

Nevado

2014

Patai's Chemistry of Functional Groups

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Gold complexes have been used to π‐activate alkynes, alkenes, and related moieties due to their strong affinity for these carbon systems. In this chapter we have summarized first, the most representative examples of gold‐catalyzed migrations occurring in propargylic systems and classified them according to the nature of the migrating group. In the second part, we have compiled the most relevant gold‐catalyzed ring expansions according to ring size. The current mechanistic understanding of these transformations is also presented.

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In Situ Generation of Nucleophilic Allenes by the Gold‐Catalyzed Rearrangement of Propargylic Esters for the Highly Diastereoselective Formation of Intermolecular C(sp³)C(sp²) Bonds

Cited by 95 publications

References 72 publications

Synthesis of α-Acyloxyketone Derivatives <i>via</i> the Platinum-Catalyzed Migration of Propargylic Esters

Synthesis of α-Acyloxyketone Derivatives <i>via</i> the Platinum-Catalyzed Migration of Propargylic Esters

Gold(I)‐Assisted α‐Allylation of Enals and Enones with Alcohols

Gold‐Catalyzed Migrations and Ring Expansions

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