Decarboxylative Aldol Reaction of α,α-Difluoro-β-keto Esters: Easy Access to Difluoroenolate

Yb(OTf)3 promoted the Krapcho decarboxylation of 2,2-difluoro-3-oxopropanoate, and a subsequent aldol reaction was achieved. This process is the first example of generating difluoroenolates through a decarboxylation-type process, and a large number of carbonyl compounds are applicable to the aldol reaction. The protocol is a complete one-pot reaction that uses the bench-stable and nonhygroscopic 2,2-difluoro-3-oxopropanoate to generate the difluoroenolate. This strategy has been applied for the synthesis of CF2-containing bioactive GABAB agonists, contributing to drug design.

Direct Deprotonative Functionalization of α,α-Difluoromethyl Ketones using a Catalytic Organosuperbase

The deprotonative functionalization of α,α-difluoromethyl ketones is described herein. Using a catalytic organosuperbase and a silane additive, the corresponding difluoroenolate could be generated and trapped with aldehydes to deliver various α,α-difluoro-β-hydroxy ketones in high yields. This new strategy tolerates numerous functional groups and represents the access to the difluoroenolate by direct deprotonation of the difluoromethyl unit. The diastereoselective version of the reaction was also investigated with d.r. up to 93 : 7. Several transformations were performed to demonstrate the synthetic potential of these α,α-difluoro-β-hydroxy ketones. In addition, this method has been extended to the use of other electrophiles such as imines and chalcogen derivatives, and a difluoromethyl sulfoxide as nucleophile, thus leading to a diversity of difluoromethylene compounds.

Synthesis of 2,2-Difluoro-3-hydroxy-1,4-diketones via an HFIP-Catalyzed Mukaiyama Aldol Reaction of Glyoxal Monohydrates with Difluoroenoxysilanes

A novel efficient HFIP-catalyzed synthesis of structurally diverse 2,2-difluoro-3-hydroxy-1,4-diketone derivatives from readily available glyoxal monohydrates and difluoroenoxysilanes is described. This convenient protocol is induced by the distinctive fluorine effect of the reactants and the fluoroalcohol catalyst, which represents the first application of fluoroalcohol catalysis in a Mukaiyama aldol reaction.

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 Brook Rearrangement Involved Domino Sequence Enabled by Acylsilane-Aldehyde Corporation

A ruthenium-catalyzed [1,2]-Brook rearrangement involved domino sequence is presented to prepare highly functionalized silyloxy indenes with atomic- and step-economy. This domino reaction is triggered by acylsilane-directed C-H activation, and the aldehyde controlled the subsequent enol cyclization/Brook Rearrangement other than β-H elimination. The protocol tolerates a broad substitution pattern, and the further synthetic elaboration of silyloxy indenes allows access to a diverse range of interesting indene and indanone derivatives.

Direct transfer of tri- and di-fluoroethanol units enabled by radical activation of organosilicon reagents

Trifluoroethanol and difluoroethanol units are important motifs in bioactive molecules, but the methods to direct incorporate these units are limited. Herein, we report two organosilicon reagents for the transfer of trifluoroethanol and difluoroethanol units into molecules. Through intramolecular C-Si bond activation by alkoxyl radicals, these reagents were applied in allylation, alkylation and alkenylation reactions, enabling efficient synthesis of various tri(di)fluoromethyl group substituted alcohols. The broad applicability and general utility of the approach are highlighted by late-stage introduction of these fluoroalkyl groups to complex molecules, and the synthesis of antitumor agent Z and its difluoromethyl analog Z'.

Acylsilane directed aromatic C-H alkenylations by ruthenium catalysis

A ruthenium-catalyzed C-H alkenylation of aroylsilanes with electron-deficient alkenes was developed, using acylsilane as the directing group. The mild reaction conditions enable the tolerance of a wide scope of functionalities such as OMe, F, Cl, Br and CF3, providing a convenient and highly effective method for the synthesis of styrene derivatives bearing acylsilane. Steroid and heterocycles such as furan and thiophene were also well tolerated. Furthermore, acylsilane was efficiently converted to the corresponding aldehyde or carboxylic acid.

Catalytic selective mono- and difluoroalkylation using fluorinated silyl enol ethers

This feature article highlights our recent achievements in catalytic selective mono- and difluoroalkylation using fluorinated silyl enol ethers (FSEEs).

Decarboxylative aldol reaction of α,α-difluoro-β-ketocarboxylate salt: a facile method for generation of difluoroenolate

We developed a decarboxylative aldol reaction using α,α-difluoro-β-ketocarboxylate salt, carbonyl compounds, and ZnCl₂/N,N,N′,N′-tetramethylethylenediamine. The generation of difluoroenolate proceeded smoothly under mild heating to provide α,α-difluoro-β-hydroxy ketones in good to excellent yield (up to 99%). The α,α-difluoro-β-ketocarboxylate salt was bench stable and easy to handle under air, which realizes a convenient and environmentally friendly methodology for synthesis of difluoromethylene compounds.

A ZnCl₂/N,N,N′,N′-tetramethylethylenediamine complex promoted decarboxylative aldol reaction of α,α-difluoro-β-ketocarboxylate salt with carbonyl compounds has been developed.

A general and efficient Lewis acid catalysed Mukaiyama-aldol reaction of difluoroenoxysilanes and ketones

We report a general and highly efficient Mukaiyama-aldol reaction of ketones and difluoroenoxysilanes. While the reaction of aryl ketones worked efficiently in the presence of Bi(OTf)₃, that of aliphatic ketones required the use of Sc(OTf)₃. In addition, Sc(OTf)₃ was capable of achieving excellent 1,2-selectivity in the corresponding reaction of α,β-unsaturated ketones. This method provides a facile access to differently substituted β-hydroxy α,α-difluoro ketones, versatile synthons for difluomethylated tertiary alcohols.

Copper-catalysed difluoroalkylation of aromatic aldehydes via a decarboxylation/aldol reaction

A copper-catalysed tandem decarboxylation/aldol reaction of simple aromatic aldehydes with 2,2-difluoro-3-oxo-3-arylpropanoic acid under mild conditions.

New Developments in Chiral Cooperative Ion Pairing Organocatalysis by Means of Ammonium Oxyanions and Fluorides: From Protonation to Deprotonation Reactions

This personal account summarizes our contribution to the ion pairing organocatalysis mainly by use of chiral quaternary or tertiary ammonium fluorides, aryloxides and carboxylates. Starting from an experimental observation, we were able to develop several approaches for the enantioselective protonation of silyl enolates and enol esters giving rise to chiral carbonyl compounds bearing a stereogenic center at the α-position. Moving from protonation to deprotonation reactions, chiral ammonium ion pair catalysts were successfully applied to several asymmetric transformations such as an Henry reaction or a direct vinylogous aldol reaction to cite a few. An outlook of further possible developments in this field of research will also be discussed.