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1.
Org Lett ; 26(9): 1926-1930, 2024 Mar 08.
Article in English | MEDLINE | ID: mdl-38407940

ABSTRACT

We herein describe a stereoselective organocatalyzed aza-Michael/Morita-Baylis-Hillman domino reaction between readily accessible acrylamides and α,ß-unsaturated carbonyls. This novel, PPh3-promoted atom economic one-pot process features medium to good yields and good stereoselectivity leading to variously substituted piperidin-2-ones bearing an exocyclic olefinic bond, which was shown to be an excellent anchor for further chemical diversification.

2.
Angew Chem Int Ed Engl ; 59(29): 11769-11773, 2020 Jul 13.
Article in English | MEDLINE | ID: mdl-32240563

ABSTRACT

Advances in the field of phosphorus chemistry are documented, by revealing the synthetic utility of previously underutilized quaternary phosphiranium salts (QPrS) as three-chain-atom electrophilic building blocks. Notably, control of their challenging C-centered electrophilicity is disclosed with an expedient synthesis of tertiary ß-anilino phosphines as a proof-of-concept.

3.
Chemistry ; 24(6): 1278-1282, 2018 Jan 26.
Article in English | MEDLINE | ID: mdl-29265547

ABSTRACT

Heavy silyl enol ethers (mostly TIPS and TBS) combine with cyclic N-alkenyl N-acyliminium salts generated in situ from their N,O-acetal precursors, to furnish highly functionalized indolizidines through an unprecedented double Mukaiyama-Mannich-Prins cascade transformation. This novel cascade annulation process demonstrates a promising scope, and takes place mostly catalytically with interesting stereocontrol. Furthermore, an appealing facet of this chemistry is emphasized with a bicatalytic approach by which the Mannich-Prins cascade follows a Ru-catalyzed N-allylamide to N-(E)-propenyl isomerization of the aminal counterpart in a one-pot operation.

4.
J Org Chem ; 82(18): 9916-9922, 2017 09 15.
Article in English | MEDLINE | ID: mdl-28812891

ABSTRACT

A completely regioselective and challenging gold(I)-catalyzed ring-opening of cyclic 1,3-dioxolanes and dioxanes by trimethylsilyl alkynes to set diol-derived propargyl trimethylsilyl bis-ethers is reported. This unprecedented and not trivial transformation does not operate with the catalytic methodologies recently reported for catalytic alkynylation of acyclic acetals/ketals, and is uniquely enabled by the application of a recently introduced synergistic gold(I)-silicon catalysis concept capable of producing simultaneously catalytic amounts of two key players, a silicon-based Lewis superacid and a nucleophilic gold acetylide.

5.
Chemistry ; 22(17): 6012-22, 2016 Apr 18.
Article in English | MEDLINE | ID: mdl-26992138

ABSTRACT

An efficient catalytic room-temperature direct α-amidoalkylation of carbonyl donors, that is, ketones and aldehydes with unbiased N,O-acetals, is described. Sn(NTf2 )4 is an optimal catalyst to promote this challenging transformation at low loading and the reaction shows promising scope. A comprehensive and rational evaluation of this reaction has led to the establishment of an empirical scale of nucleophilic reactivity for a broad set of ketones that should be helpful in the synthetic design and development of carbonyl α-functionalization methods.

6.
Org Lett ; 17(9): 2130-3, 2015 May 01.
Article in English | MEDLINE | ID: mdl-25875696

ABSTRACT

The combined use of Tf2NH and L(Au)(+)X(-) as a dual or binary catalytic system clearly improves the efficiency and enlarges the scope of the tandem intermolecular Friedel-Crafts α-amidoalkylation/intramolecular hydroarylation sequence, compared to an "all gold" multicatalysis approach.

7.
J Org Chem ; 79(5): 1900-12, 2014 Mar 07.
Article in English | MEDLINE | ID: mdl-24533649

ABSTRACT

Intramolecular and intermolecular alkylations of carbocation precursors of limited ionization ability, principally N,O-acetals, without the use of an exogenous reagent have been developed. The reactions are carried out in 1,1,2,2-tetrachloroethane (TCE) and take advantage of the ability of this solvent to continuously release small amounts of HCl by thermolytic elimination. A study of the reaction led to several improved protocols such as (1) preheated TCE, (2) microwave-assisted reactions, and (3) flow or sealed-tube conditions, which allow significant reaction rate enhancements and made possible some challenging reactions such as the α-amidoalkylation of ketones. Studies using flow chemistry confirmed not only that very low concentrations of HCl generated from the solvent were responsible for the reactivity but also that TCE had additional beneficial properties in comparison to other chlorinated solvents such as dichloroethane. The method can easily be extended to the alkylation using proelectrophiles such as π-activated alcohols, which are normally unreactive toward HCl catalysis. This work represents the first successful use of HCl, the simplest strong Brønsted acid, as an efficient alkylation catalyst.


Subject(s)
Acetals/chemistry , Alcohols/chemistry , Ethane/analogs & derivatives , Hydrocarbons, Chlorinated/chemistry , Alkylation , Catalysis , Ethane/chemistry , Indicators and Reagents/chemistry , Microwaves , Molecular Structure , Solvents/chemistry
8.
Chemistry ; 18(44): 14192-200, 2012 Oct 29.
Article in English | MEDLINE | ID: mdl-22996700

ABSTRACT

Gold catalysts have been applied in cascade-type reactions for the synthesis of different nitrogen-based compounds. The reactions likely proceed by a new gold-catalyzed cascade intermolecular α-amidoalkylation/intramolecular carbocyclization cascade process by unifying both the σ- and π-Lewis acid properties of the gold salts. In the first part of this report we show that the σ-Lewis acidity of gold(I) and gold(III) could be exploited to efficiently catalyze the nucleophilic substitution of various alkoxy- and acetoxylactams. The reaction was found to be applicable to a wide range of cyclic N-acyliminium ion precursors and various nucleophiles, including allyltrimethylsilane, silyl enol ethers, arenes, and active methylene derivatives. As a logical progression of this study, a combined hard/soft binary catalytic gold system was then used to implement an unprecedented tandem intermolecular Friedel-Crafts amidoalkylation/intramolecular hydroarylation sequence allowing an expedient access to new, complex, fused polyheterocyclic structures from trivial materials.

9.
Chem Soc Rev ; 41(5): 1696-707, 2012 Mar 07.
Article in English | MEDLINE | ID: mdl-22045014

ABSTRACT

Over the last decade, with the surge in the development of organocatalysis, many processes involving chiral ion pairs have emerged as powerful tools in the design of new efficient organocatalysts. This tutorial review focuses on the recent evolutions of these organocatalytic systems in which both anionic and cationic parts are working in a cooperative fashion in order to develop unique catalytic processes which outperform the existing approaches. In this respect, chiral ion pairs opened new avenues in the design of bifunctional organocatalysts by means of combinatorial approaches.


Subject(s)
Ions/chemistry , Catalysis , Hydrogen Bonding , Lewis Bases/chemistry , Static Electricity , Stereoisomerism
10.
J Org Chem ; 75(22): 7704-16, 2010 Nov 19.
Article in English | MEDLINE | ID: mdl-20958068

ABSTRACT

In the present work, enantioselective protonation of silyl enol ethers is reported by means of a variety of chiral nitrogen bases as catalysts, mainly derived from cinchona alkaloids, in the presence of various protic nucleophiles as proton source. A detailed study of the most relevant reaction parameters is disclosed allowing high enantioselectivities of up to 92% ee with excellent yields to be achieved under mild and eco-friendly conditions. The synthetic utility of this organocatalytic protonation was demonstrated during the preparation of two homoisoflavones 4a and 4b, isolated from Chlorophytum Inornatum and Scilla Nervosa, which were obtained with 81% and 78% ee, respectively.


Subject(s)
Cinchona Alkaloids/chemistry , Ethers/chemistry , Isoflavones/chemistry , Silanes/chemistry , Catalysis , Molecular Structure , Stereoisomerism
11.
Angew Chem Int Ed Engl ; 49(43): 7860-88, 2010 Oct 18.
Article in English | MEDLINE | ID: mdl-20715025

ABSTRACT

The continuously increasing need for novel and selective methods in organic synthesis to aid drug discovery and to address environmental concerns is a constant source of stimulation to develop novel and more efficient reaction systems. This has often resulted in a focus on transition metals, ligands, and additives, with much less attention paid to the counterion(s) of the metal cation. Recently, metal salts with one or more triflimidate counterion(s) have appeared as a unique class of catalysts that display outstanding σ- and π-Lewis acid character. The highly delocalized nature of the triflimidate counterion, combined with its high steric hindrance results in virtually no nucleophilic behavior and an extremely high positive charge density on the metal cation, thus enhancing its Lewis acid character. Consequently, these metal triflimidates often outperform their metal halide or triflate analogues. This Review describes general methods for the preparation of metal triflimidate salts and their use as catalysts.

13.
J Org Chem ; 73(18): 7067-71, 2008 Sep 19.
Article in English | MEDLINE | ID: mdl-18712925

ABSTRACT

The straightforward syntheses of C3v symmetrical calix[6]trisureas and -thiourea have been achieved. NMR studies have shown that these flexible compounds possess a major cone conformation. While these neutral hosts can strongly bind anions such as AcO(-) or HSO4(-) through induced fit processes, they can also behave as unique heteroditopic receptors for organic ion pairs with a remarkable positive cooperativity in the complexation process, the anion acting as an allosteric effector.


Subject(s)
Calixarenes/chemistry , Phenols/chemistry , Thiourea/analogs & derivatives , Thiourea/chemistry , Urea/analogs & derivatives , Urea/chemistry , Binding Sites , Calixarenes/chemical synthesis , Ions/chemistry , Magnetic Resonance Spectroscopy/methods , Magnetic Resonance Spectroscopy/standards , Molecular Conformation , Phenols/chemical synthesis , Reference Standards , Stereoisomerism , Thiourea/chemical synthesis , Urea/chemical synthesis
15.
Org Lett ; 7(23): 5335-7, 2005 Nov 10.
Article in English | MEDLINE | ID: mdl-16268572

ABSTRACT

[reaction: see text] In situ formed N-trialkylsilyl bistrifluoromethanesulfonimides (R3SiNTf2) species have been shown to efficiently catalyze the nucleophilic substitution reactions of chiral 5-oxypyrrolidin-2-ones by silicon-based nucleophiles. The reaction rates were significantly accelerated in comparison to the cases where the usual triflate catalysts are used. Adducts were obtained in high yields and usual stereoselectivities within short reaction times, and the process was compatible with a semipreparative scale.

16.
Org Lett ; 7(14): 2825-8, 2005 Jul 07.
Article in English | MEDLINE | ID: mdl-15987146

ABSTRACT

[reaction: see text] Nucleophilic substitution reactions of racemic and chiral 5-acetoxy-, 5-ethoxy-, and 5-methoxypyrrolidin-2-ones by silicon-based nucleophiles were efficiently catalyzed by TIPSOTf. This process was found to be general and accommodates a broad range of substrate-nucleophile combinations.

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