A regioselective carbosilylation of alkenes has emerged as a powerful strategy to access molecules with functionalized silylated alkanes, by incorporating silyl and carbon groups across an alkene double bond. However, to the best of our knowledge, organic fluorides have never been used in this protocol. Here we disclose the catalyst-free carbosilylation of alkenes using silyl boronates and organic fluorides mediated by tBuOK. The main feature of this transformation is the selective activation of the C-F bond of an organic fluoride by the silyl boronate without undergoing potential side-reactions involving C-O, C-Cl, heteroaryl-CH, and even CF3 groups. Various silylated alkanes with tertiary or quaternary carbon centers that have aromatic, hetero-aromatic, and/or aliphatic groups at the β-position are synthesized in a single step from substituted or non-substituted aryl alkenes. An intramolecular variant of this carbosilylation is also achieved via the reaction of a fluoroarene with a ω-alkenyl side chain and a silyl boronate.
A simple
protocol to overcome the explosive pentafluoroethylation
of carbonyl compounds by HFC-125 is described. The use of potassium
(K) bases with triglyme or tetraglyme as a solvent safely yields the
pentafluoroethylation products in good to high yields. The experimental
results suggest that an encapsulation of the K cation by glymes as
K(glyme)2 inhibits the contact between the K cation and
the reactive anionic pentafluoroethyl counterion, preventing their
transformation into KF and explosive tetrafluoroethylene (TFE). The
generation of sterically demanding [K(G3)2]+ and [K(G4)2]+ is an effective way as an unstable
pentafluoroethyl anion reservoir.
Fluoroform,
HFC-23, is an industrial byproduct from the synthesis
of polytetrafluoroethylene and is a vastly underused resource; however,
its physicochemical properties have hindered progress toward synthetic
uses. Herein, we describe the use of HFC-23 as a cheap trifluoromethylating
agent in two reactions for the highly diastereoselective synthesis
of medicinally attractive chiral amines with two stereogenic carbon
centers: a base-dependent, stereodivergent nucleophilic addition to
synthesize enantioenriched vicinal diamines and a tandem nucleophilic
addition/aza-Michael sequence toward enantioenriched isoindolines.
The protocol of micro-flow nucleophilic pentafluoroethylation using pentafluoroethane (HC 2 F 5 , HFC-125), a nontoxic, inexpensive, and commercially available greenhouse gas, is described. The micro-flow pentafluoroethylation by HFC-125 proceeded smoothly at room temperature or at −10 °C in DMF or toluene in the presence of a potassium base, namely, t-BuOK or KHMDS. A broad range of ketones, aldehydes, and chalcones with various substituted benzene rings were successfully converted to the corresponding pentafluoroethyl carbinols instantly with good to high yields.
A straightforward method that enables the formation of biologically attractive trifluoromethyl ketones from readily available methyl esters using the potent greenhouse gas fluoroform (HCF3, HFC-23) was developed. The combination of fluoroform and KHMDS in triglyme at −40 °C was effective for this transformation, with good yields as high as 92%. Substrate scope of the trifluoromethylation procedure was explored for aromatic, aliphatic, and conjugated methyl esters. This study presents a straightforward trifluoromethylation process of various methyl esters that convert well to the corresponding trifluoromethyl ketones. The tolerance of various pharmacophores under the reaction conditions was also explored.
A protocol for the stereodivergent pentafluoroethylation
of N-sulfinylimines using HFC-125 with KHMDS/triglyme
has been
developed. Both diastereomers of the pentafluoroethylated amines can
be selectively synthesized based on the presence or absence of triglyme.
This additive-controlled protocol allows the KHMDS/triglyme cryptate
to be a straightforward and cheap alternative to previously reported
base-controlled stereodivergent trifluoromethylation using potassium
hexamethyldisilazide (KHMDS) versus P4-
t
Bu.
Hydrofluorocarbons (HFCs) are widely used as cooling agents in refrigerators and air conditioners and as solvents in industrial processes. However, their application has been restricted by their high global warming potential. Thus, strategies for HFC decomposition and effective utilization are urgently required. Herein, we describe a method for the chemical transformation of two HFCs, viz. HFC-23 and HFC-125, based on the continuous-flow perfluoroalkylation of esters to synthesize the pharmaceutically and agrochemically vital trifluoromethyl and pentafluoroethyl ketones. The combination of a potassium base and a glyme solvent system is found to be the most effective. The proposed method is attractive for industrial use because it allows the consumption of a large volume of HFCs, promotes the synthesis of high-value medicinal compounds, and serves as an ideal alternative to the current HFC decomposition processes like thermal plasma treatment.
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