Organopotassium‐Catalyzed Silylation of Benzylic C(sp3)−H Bonds
Baptiste Neil,
Lamine Saadi,
Louis Fensterbank
et al.
Abstract:Benzylsilanes have found increasing applications in organic synthesis as bench-stable synthetic intermediates, yet are mostly produced by stoichiometric procedures. Catalytic alternatives based on the atomeconomical silylation of benzylic C(sp 3 )À H bonds remain scarcely available as specialized directing groups and catalytic systems are needed to outcompete the kinetically-favored silylation of C(sp 2 )À H bonds. Herein, we describe the first general and catalytic-in-metal undirected silylation of benzylic C… Show more
Aryl-and alkyldiimides (R−N�NH with R = aryl or alkyl) are elusive intermediates of valuable synthetic use, as they are assumed to be transient species in processes involving both carbon (with concomitant loss of N 2 ) and nitrogen nucleophiles (with conservation of the N�N moiety). The actual compounds are fragile and as such not bench stable which is why they have not yet found the attention they deserve. Conversely, early contributions showed that the stability of the parent diimide is significantly increased by replacing the hydrogen atom by a silyl group, but the synthetic applicability of these silicon-protected aryl-and alkyldiazenes has been far less explored, in part due to the absence of general procedures for their preparation. This Perspective provides an overview of the underexplored diazene chemistry that has witnessed considerable progress in recent years and highlights the potential of this motif in a range of synthetically useful (catalytic) transformations. The rediscovered siliconmasked diazenes constitute a versatile platform possessing enhanced stability and tamed reactivity in comparison to the parent hydrogen-substituted diimides. Aryl, diazenyl, and alkyl anionic key intermediates can be selectively generated in situ under Lewis base or transition metal catalysis, giving rise to novel synthetic approaches as viable alternatives to the already existing methodologies.
Aryl-and alkyldiimides (R−N�NH with R = aryl or alkyl) are elusive intermediates of valuable synthetic use, as they are assumed to be transient species in processes involving both carbon (with concomitant loss of N 2 ) and nitrogen nucleophiles (with conservation of the N�N moiety). The actual compounds are fragile and as such not bench stable which is why they have not yet found the attention they deserve. Conversely, early contributions showed that the stability of the parent diimide is significantly increased by replacing the hydrogen atom by a silyl group, but the synthetic applicability of these silicon-protected aryl-and alkyldiazenes has been far less explored, in part due to the absence of general procedures for their preparation. This Perspective provides an overview of the underexplored diazene chemistry that has witnessed considerable progress in recent years and highlights the potential of this motif in a range of synthetically useful (catalytic) transformations. The rediscovered siliconmasked diazenes constitute a versatile platform possessing enhanced stability and tamed reactivity in comparison to the parent hydrogen-substituted diimides. Aryl, diazenyl, and alkyl anionic key intermediates can be selectively generated in situ under Lewis base or transition metal catalysis, giving rise to novel synthetic approaches as viable alternatives to the already existing methodologies.
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