Enantio- and Diastereoselective Tandem Zn-Promoted Brook Rearrangement/Ene−Allene Carbocyclization Reaction

Nucleophilic Allylation of Acylsilanes in Water: An Effective Alternative to Functionalized Tertiary α-Silylalcohols

A nucleophilic allylation of acylsilanes in water was developed, generating versatile functionalized tertiary α-silyl alcohols in high yields. With the assistance of hydrogen bonding, a reaction model of less reactive acylsilane was achieved. Unlike the conventional strategy, transition metals and an additional Lewis acid catalyst were not required, and rate acceleration was observed in water.

Bimetallic tandem catalysis-enabled enantioselective cycloisomerization/carbonyl-ene reaction for construction of 5-oxazoylmethyl α-silyl alcohol

A bimetallic tandem catalysis-enabled enantioselective cycloisomerization/carbonyl-ene reaction was developed. The reaction proceeded well with a broad range of N-propargylamides and acylsilanes, affording the target chiral 5-oxazoylmethyl α-silyl alcohols in up to 95% yield and 99% ee under mild conditions. Importantly, this facile protocol was available for the late-stage modification of several bioactive molecules. Based on the mechanistic study and control experiments, a possible catalytic cycle and transition state are proposed to elucidate the reaction process and enantioinduction.

Cascade cyclization of alkene-tethered acylsilanes and allylic sulfones enabled by unproductive energy transfer photocatalysis

Developing photo-induced cascade cyclization of alkene-tethered acylsilanes is challenging, because acylsilanes are unstable under light irradiation. Herein, we report that the energy transfer from excited acylsilanes to a photocatalyst that possesses lower triplet energy can inhibit the undesired decomposition of acylsilanes. With neutral Eosin Y as the photocatalyst, an efficient synthesis of cyclopentanol derivatives is achieved with alkene-tethered acylsilanes and allylic sulfones. The reaction shows broad substrate scope and the synthetic potential of this transformation is highlighted by the construction of cyclopentanol derivatives which contain fused-ring or bridged-ring.

Acylsilanes decompose under light irradiation, and this limits their use in light-induced organic transformations. Here the authors report a strategy to inhibit the light-induced decomposition of acylsilanes, enabling the photochemical synthesis of cyclopentanol derivatives from alkene-tethered acylsilanes and allylic sulfones.

Direct synthesis and applications of solid silylzinc reagents

The increased synthetic utility of organosilanes has motivated researchers to develop milder and more practical synthetic methods. Silylzinc reagents, which are typically the most functional group tolerant, are notoriously difficult to synthesize because they are obtained by a pyrophoric reaction of silyllithium, particularly Me3SiLi which is itself prepared by the reaction of MeLi and disilane. Furthermore, the dissolved LiCl in silylzinc may have a detrimental effect. A synthetic method that can avoid silyllithium and involves a direct synthesis of silylzinc reagents from silyl halides is arguably the simplest and most economical strategy. We describe, for the first time, the direct synthesis of PhMe2SiZnI and Me3SiZnI reagents by employing a coordinating TMEDA ligand, as well as single crystal XRD structures. Importantly, they can be obtained as solids and stored for longer periods at 4 °C. We also demonstrate their significance in cross-coupling of various free alkyl/aryl/alkenyl carboxylic acids with broader functional group tolerance and API derivatives. The general applicability and efficiency of solid Me3SiZnI are shown in a wide variety of reactions including alkylation, arylation, allylation, 1,4-addition, acylation and more.

Ruthenium-catalyzed C-H amination of aroylsilanes

Acylsilane represents a valuable synthon in synthetic chemistry. We report on ruthenium(ii)-catalyzed ortho-C-H amination of aroylsilanes to provide facile access to synthetically useful imidobenzoylsilanes and tosyl-amidobenzoylsilanes. The protocols, with broad substrate scope and excellent functional group tolerance, are enabled with the weak chelation-assistance of acylsilane via C-H cyclometallation.

Enantioselective Insertion of Alkynyl Carbenes into Si-H Bonds: An Efficient Access to Chiral Propargylsilanes and Allenylsilanes

Chiral propargylsilanes and chiral allenylsilanes have emerged as versatile building blocks for organic synthesis. However, efficient methods for preparing these organosilicon compounds are lacking. We herein report a highly enantioselective method for synthesis of chiral propargylsilanes and chiral allenylsilanes from readily available alkynyl sulfonylhydrazones. Specifically, chiral spiro phosphate dirhodium complexes were used to catalyze asymmetric insertion of alkynyl carbenes into the Si-H bonds of silanes to afford a variety of chiral propargylsilanes with excellent enantioselectivity. Subsequently, a platinum catalyst was used for stereospecific isomerization of the chiral propargylsilanes to the corresponding chiral allenylsilanes.

Catalytic asymmetric addition of thiols to silyl glyoxylates for synthesis of multi-hetero-atom substituted carbon stereocenters

A chiral Lewis acid-catalyzed enantioselective addition of thiols to silyl glyoxylates was developed. The reaction proceeds well with a broad range of thiols and acylsilanes, affording the target tertiary chiral α-silyl–α-sulfydryl alcohols with multi-hetero-atom carbon stereocenters in excellent yields (up to 99%) and enantioselectivities (up to 98% ee). A series of control experiments were conducted to elucidate the reaction mechanism.

Enantioselective addition of thiols to silyl glyoxylates for construction of a multi-hetero-atom substituted carbon stereocenter was described.

Aqueous ZnCl2 Complex Catalyzed Prins Reaction of Silyl Glyoxylates: Access to Functionalized Tertiary α-Silyl Alcohols

An efficient Prins reaction of silyl glyoxylates in the presence of an aqueous ZnCl₂ complex as a catalyst was developed, providing functionalized tertiary α-silyl alcohols in high yields under mild conditions. A preliminary investigation indicated that the aqueous ZnCl₂ complex acted as a dual functional catalyst of Brønsted and Lewis acid to activate the carbonyl groups of silyl glyoxylates via a dual-activation model.

A general protocol for radical anion [3 + 2] cycloaddition enabled by tandem Lewis acid photoredox catalysis

We report herein a method for intermolecular [3 + 2] cycloaddition between aryl cyclopropyl ketones and alkenes involving the combination of Lewis acid and photoredox catalysis. In contrast to other more common methods for [3 + 2] cycloaddition, these conditions operate using a broad range of both electron-rich and electron-deficient reaction partners. The critical factors predicting the success of these reactions is the redox potential of the cyclopropyl ketone and the ability of the alkene to stabilize a key radical intermediate.

A catalyst-controlled switchable reaction of β-keto acids to silyl glyoxylates

A catalyst-controlled switchable reaction of β-keto acids to silyl glyoxylates was developed and the decarboxylative-addition products were generated by using a thiourea catalyst.

Enantioselective synthesis of chiral acylsilanes by copper/HZNU-Phos-catalyzed asymmetric conjugate addition of diethyzinc to α,β-unsaturated acylsilanes

The catalytic asymmetric copper-catalyzed conjugate addition of diethylzinc reagent to α,β-unsaturated acylsilanes was found to proceed smoothly in moderate to good yields and enantioselectivities (up to 85% ee) in the presence of the multifunctional HZNU-Phos.

Copper-catalyzed enantioselective additions to oxocarbenium ions: alkynylation of isochroman acetals

We have developed an enantioselective, copper(I)-catalyzed addition of terminal alkynes to racemic isochroman acetals. This method is one of the first transition-metal-catalyzed approaches to enantioselective additions to prochiral oxocarbenium ions. In this reaction, TMSOTf is used to form the oxocarbenium ion in situ under conditions compatible with simultaneous formation of the chiral copper acetylide. By using a bis(oxazoline) ligand, good yields and enantioselectivities are observed for a variety of enantioenriched 1-alkynyl isochromans.

Benzyl and phenylthiomethyl silanes: a new class of bifunctional linchpins for type II anion relay chemistry (ARC)

A new class of bifunctional linchpins bearing electrophilic sites beta or gamma to a silyl group have been designed, synthesized, and demonstrated to be competent in tricomponent unions exploiting Type II Anion Relay Chemistry (ARC). High diastereoselectivities were observed when a phenyl moiety (R(2)) served as an anion-stabilizing group (ASG) adjacent to a methyl susbtituent (R(1)), while diastereomeric mixtures were obtained when a phenylthiol moiety served as the ASG, irrespective of alpha-substitution.