Vinyl Cation Stabilization by Silicon Enables a Formal Metal‐Free α‐Arylation of Alkyl Ketones

Abstract

The ability of silicon to stabilize vinyl cationic species leads to a redox arylation of alkynes whereby the stringent limitations of reactivity and regioselectivity of alkyl‐substituted alkynes are lifted. This allows the synthesis of a range of α‐silyl‐α′‐arylketones under mild conditions in good to excellent yields and with high functional group tolerance, whereby the silicon moiety in the final products can either be removed for a formal acetone monoarylation transform, or capitalized upon for subsequent electrophilic substitutions at either side of the carbonyl group.

Stereodivergent Alkyne Hydrofluorination Using a Simple Practical Reagent

“…A range of primary, secondary, cyclic or acyclic alkyl-substituted alkynes could be employed in the hydrofluorination to furnish respective products again with moderate to good yields and excellent regio-and stereoselectivities (27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39). Remarkably, substrates with potentially sensitive functional groups including a primary chloro, a carboxymethyl, a cyano, a pyridyl, and a phthalimido group also delivered the monofluoroalkene products, highlighting the mildness and good functional group tolerance of this protocol (40)(41)(42)(43)(44)(45)(46). This scalability of the procedure was demonstrated by the gram-scale preparation of 44, which proceeded with unchanged regio-and stereoselectivities and only a slightly reduced yield (1.65 g, 64%).…”

“…They also provide insight into the excellent stereochemical control and accounts for the ability to selectively obtain the E or Z isomer through the variation of reagent and reaction conditions. Previously, vinyl cations have been generated through several approaches 36 , including metal catalysis 37,38 , photochemical processes 39 , ionization of vinyl iodonium 40 and diazonium species 41 , (pseudo)halide abstraction with Lewis acids 42,43 , as well as protonation of alkynes with strong Brønsted acid 44,45 . In spite of the challenging and specialized conditions that are often required for their generation, the versatility of this intermediate has led to a recent renaissance in their synthetic applications 46 .…”

Facile C–S Bond Cleavage of Aryl Sulfoxides Promoted by Brønsted Acid

“…Addition of a Brønsted acid to a sulfoxide presumably leads to association with the highly polarized sulfoxide oxygen. 14 Alternatively, protonation on the electron-rich arene would generate a short-lived intermediate 4, which would rapidly be intercepted by the nucleophilic thiol generating the product 2 and one equivalent of thiosulfinate 5. The thiosulfinate formed in this process is not stable under the reaction conditions and further reacts to give a mixture of symmetrical and unsymmetrical disulfides as the only detectable byproducts.…”

Stereodivergent Alkyne Hydrofluorination Using Protic Tetrafluoroborates as Tunable Reagents

“…Previously,vinyl cations have been generated through several approaches, [23] including metal catalysis, [24,25] photochemical processes, [26] ionization of vinyl iodonium [27] and diazonium species, [28] (pseudo)halide abstraction with Lewis acids, [29,30] as well as protonation of alkynes with astrong Brønsted acid or aB rønsted/Lewis acid complex. [31,32] Despite the challenging and specialized reaction conditions that are often required for their generation, the versatility of this intermediate has led to ar ecent renaissance in their synthetic applications. [33] In this context, the hydrofluorination conditions reported here represent an unprecedentedly mild, stereocontrolled, and functional-group compatible approach for utilizing these intermediates.…”