Synthesis of α‐Trifluoromethylated Ketones from Vinyl Triflates in the Absence of External Trifluoromethyl Sources

Abstract

Anovel method for the conversion of vinyl triflates into a-trifluoromethylated ketones in the absence of external trifluoromethyl sources is described. This process accomplishes an efficient migration of the trifluoromethyl group of the triflate to the a-position in the ketone through ar adical process.T he reaction proceeds by the addition of at rifluoromethyl radical to the vinyl triflate and subsequent fragmentation of the trifluoromethane sulfonyl radical. Based on this reaction, aone-pot two-step procedure for the trifluoromethylation of ketones was developed. The method presented herein also allows the transfer of perfluoroalkyl groups from vinyl perfluoroalkanesulfonates,w hicha re readily accessible from alkynes and perfluoroalkanesulfonic acids.

A base-controlled switch of SO2 reincorporation in photocatalyzed radical difunctionalization of alkenes

“…Evaluation of the reaction conditions Due to the low bond dissociation energy of the O-S bond, enol triflates could undergo desulfurization-fragmentation, followed by formal addition over multiple bonds of enol Article triflates to generate a-trifluoromethylated ketones in a catalytic manifold. 46,48,49 In principle, enol triflates can be divided into three components, namely the trifluoromethyl group, SO 2 , and the ketone moiety. To evaluate the hypothesized switchable use of enol triflate as bifunctional or trifunctional reagents to generate distinct products from the same alkene feedstocks, phenyl enol triflate (1a) was used as a functional reagent and 1-hexene (2a) served as the radical acceptor (Figure 2).…”

“…In this regard, g-trifluoromethylated ketones and trifluoromethylated sulfonyl ketones are important building blocks (Figure 1C). [41][42][43][44][45][46][47] Nonetheless, methods for the synthesis of both types of compounds have been seldomly reported. Herein, a base-controlled reincorporation/release of SO 2 within a photocatalyzed radical difunctionalization of alkenes is described, offering a switchable gateway toward a series of otherwise difficult-to-obtain g-trifluoromethylated ketones and trifluoromethylated sulfonyl ketones (Figure 1B).…”

Facile Synthesis of α-N-Heterocyclic Carbene-Boryl Ketones from N-Heterocyclic Carbene-Boranes and Alkenyl Triflates

“…Further, the added NHCborane spoiled the default reactionthe α-trifluoromethyl ketone was not formed either. Under Kamimura's conditions 11 (Et 3 B, ambient air, ClCH 2 CH 2 Cl), the α-NHC-boryl ketone 10a was formed, but only in small amounts according to 11 B NMR analysis.…”

“…However, we soon found that the target reaction proceeded rather smoothly when all the other reagents were replaced by a simple tert-amine (Scheme 1). For example, heating of NHCborane 8, alkenyl triflate 9a (1.3 equiv), and diisopropyl ethyl amine (iPr 2 NEt, 0.8 equiv) in THF at 66 °C for 3 h provided α-NHC-boryl ketone 10a in 66% yield according to 11 B NMR analysis of the reaction mixture. Solvent evaporation and flash chromatography provided pure 10a in 50% yield as a stable white solid.…”

“…The results of a scope study with readily available alkenyl triflates are summarized in Figure 3, which shows structures of α-boryl ketone products, 11 B NMR yields, and isolated yields (in parentheses) of the various products that were prepared. The standard procedure from Scheme 1 was used in all of these experiments (0.1 mmol NHC-borane 8; alkenyl triflate, 1.3 equiv; iPr 2 NEt, 0.8 equiv, THF, 66 °C, 3 h).…”