N-Benzyloxyacrylamides as Bisnucleophiles in an Organocatalyzed Domino aza-Michael/Morita-Baylis-Hillman Sequence.

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.

Taming the Reactivity of Phosphiranium Salts: Site-Selective C-Centered Ring Opening for Direct Synthesis of Phosphinoethylamines.

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.

Novel Hybrid Prins/Aza-Prins Oxocarbenium/N-Acyliminium Cascade: Expedient Access to Complex Indolizidines.

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.

Catalytic Alkynylation of Cyclic Acetals and Ketals Enabled by Synergistic Gold(I)/Trimethylsilyl Catalysis.

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.

Enolizable Carbonyls and N,O-Acetals: A Rational Approach for Room-Temperature Lewis Superacid-Catalyzed Direct α-Amidoalkylation of Ketones and Aldehydes.

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.

Sequential Friedel-Crafts-Type α-Amidoalkylation/Intramolecular Hydroarylation: Distinct Advantage of Combined Tf2NH/Cationic LAu(I) as a Consecutive or Binary Bicatalytic System.

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.

Intra- and intermolecular alkylation of N,O-acetals and π-activated alcohols catalyzed by in situ generated acid.

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.

Dual hard/soft gold catalysis: intermolecular Friedel-Crafts-type α-amidoalkylation/alkyne hydroarylation sequences by N-acyliminium ion chemistry.

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.

Enantioselective catalytic ring expansion of methylenecyclopropane carboxamides promoted by a chiral magnesium Lewis acid.

A catalytic enantioselective ring expansion of monoactivated methylenecyclopropanes (MCP) in the presence of N-tosyl aldimines was developed using a chiral bis(oxazoline) ligand-MgI2 complex. After evaluation of ligands and optimization of the reaction conditions, the reaction has been applied to a variety of aromatic and heteroaromatic aldimines providing the corresponding trans-C2,C3-disubstituted methylenepyrrolidines in generally good yields (greater than 52%) and up to 86% ee. [reaction: see text].

Synthetic approaches and total synthesis of natural zoapatanol.

[structure: see text] The total synthesis of (+)-zoapatanol utilizing an intramolecular Horner-Wadsworth-Emmons olefination and an enantioselective Sharpless dihydroxylation as the key steps has been achieved. An advanced oxepene intermediate has been obtained by applying a ring-closing metathesis to an unsaturated enol ether.

Synthesis of omega-hydroxy ketones from omega-benzyloxy Weinreb amides by using a chemoselective nucleophilic addition/Birch reduction process.

[reaction: see text] A chemoselective nucleophilic addition/Birch reduction process applied to omega-benzyloxy Weinreb amides led to omega-hydroxy ketones in good yields.

Total synthesis of natural (+)-(2's,3'r)-zoapatanol.

[reaction: see text] (+)-Zoapatanol was synthesized by using four key-steps: a Suzuki cross-coupling to prepare a (Z)-alpha,beta-unsaturated ester followed by an enantioselective dihydroxylation to control the C2' and C3' stereocenters, an intramolecular Horner-Wadsworth-Emmons olefination to construct the oxepane ring, and a chemoselective nucleophilic addition/Birch reduction process of a Weinreb amide to introduce simultaneously the beta,gamma-unsaturated ketone on the side-chain and regenerate alcohols from benzyl ethers.