Reaction of silylallenes with triplet molecular oxygen

Abstract

A facile formal ene reaction of trisubstituted silylallenes with triplet molecular oxygen involving the cleavage of a C(sp2)–H bond has been described.

2H-Imidazol-2-oneO-Oxide: A Criegee Intermediate from a σ0π2Singlet Ground-State Carbene

“…Molecular dioxygen, 3 O 2 , despite being a “high-energy” paramagnetic diradical, is commonly reluctant to undergo low barrier reactions with closed-shell molecules. , Therefore, exceptions to this conventional wisdom attract our attention and make us ponder. − Being a diradical, dioxygen’s reactivity is rather different when it comes to binding with other open-shell species such as mono- and diradicals. In this regard, hydrocarbon radicals often recombine barrierlessly with 3 O 2 under the formation of peroxy radicals in combustion and atmospheric environments. − In a similar vein, triplet carbenes react readily with triplet O 2 in an overall spin-allowed reaction at a rate near the diffusion limit. − The products of these reactions, namely, carbonyl O -oxide Criegee intermediates (CI, R 2 CO + –O – ), are also the central intermediates in the (atmospheric) alkene ozonolysis and are involved in autoxidation chemistry. ,− In contrast to the high reactivity of triplet carbenes, singlet carbenes often do not react with 3 O 2 or at a much lower rate. − Hence, CIs formally arising from singlet carbenes are frequently poorly characterized, which is unfortunate because they may enjoy significant stereoelectronic stabilization .…”

Propargyl Radicals in Organic Synthesis

“…Lee et al have used silylated allenes in a formal ene reaction with molecular oxygen. [16] The silyl group was essential in inducing peroxide formation. The bond dissociation energy of allenic C(sp 2 )À H bonds should be lower and comparable to that of typical allylic C(sp 3 )À H bonds.…”

“…Lee et al. have used silylated allenes in a formal ene reaction with molecular oxygen [16] . The silyl group was essential in inducing peroxide formation.…”

Pericyclic Cascade Reactions Affording Thienyl- and Benzo[b]thienyl-Fused Architectures: A Synthetic and Density Functional Theory Analysis of Asynchronous Diels–Alder Reactions of Thioarylmaleimides

“…Given that light is not necessary for the formation of 9c, the most likely mechanism is via the reaction of H a ′ of 4c with triplet oxygen to give peroxide intermediate 8c, followed by spontaneous reduction to give hydroxylated 9c. 28,29 Although ene reactions with singlet oxygen are generally known to proceed in a concerted fashion with retention of stereochemistry, these details are unclear in this case and are worthy of investigation in a future study.…”