Rhodium-Catalyzed Remote Isomerization of Alkenyl Alcohols to Ketones

Abstract

We develop herein an efficient rhodium-catalyzed remote isomerization of aromatic and aliphatic alkenyl alcohols into ketones. This catalytic process, with a commercially available catalyst and ligand ([RhCl(cod)] 2 and Xantphos), features high efficiency, low catalyst loading, good functional group tolerance, a broad substrate scope, and no (sub)stoichiometric additive. Preliminary mechanistic studies suggest that this transformation involves an iterative dissociative β-hydride elimination−migration insertion process.

Conversion of Primary Alcohols and Butadiene to Branched Ketones via Merged Transfer Hydrogenative Carbonyl Addition–Redox Isomerization Catalyzed by Rhodium

“…Preexisting methods of this type include hydroacylation (which typically requires β-chelating groups to suppress decarbonylation), , “oxa-Heck” reactions (which are restricted to aryl transfer), − two reports of the reductive coupling of styrenes with anhydrides, , and, finally, recently reported formate-mediated reductive coupling–redox isomerizations of aldehydes and vinyl halides or triflates . Here, we report a method for the direct redox–neutral conversion of primary benzylic or aliphatic alcohols and butadiene (12 × 10 6 tons/year) to branched ketones via merged transfer hydrogenative carbonyl addition–redox isomerization. − These processes represent the first examples of rhodium-catalyzed carbonyl addition via hydrogen autotransfer. , …”

“…Crossover of deuterium or hydrogen into the resulting ketones deuterio - 3a″ and 3i′ is not observed. The collective data suggest that both formation of the allylrhodium intermediate from butadiene and internal redox isomerization , occur via rapid, reversible, and nonregioselective hydrometalation events and that the kinetic rhodium alkoxide enacts redox–isomerization without dissociation of rhodium at any intervening stage.…”

“…Hydrorhodation of butadiene delivers a nucleophilic allylrhodium­(I) species that participates in aldehyde addition to form a branched homoallylic rhodium­(I) alkoxide. This homoallylic rhodium­(I) alkoxide affects redox isomerization , through a series of β-hydride elimination hydrorhodation events to provide a rhodium enolate, which upon exchange with reactant alcohol releases the isobutyl ketone and regenerates the primary rhodium­(I) alkoxide to close the catalytic cycle. As established by the double-labeling crossover experiment (Scheme ), dissociation of rhodium does not occur at any stage during the course of redox isomerization.…”

Nickel-Catalyzed Isomerization/Allylic Cyanation of Alkenyl Alcohols

“…Remote functionalization mediated by alkene isomerization is a powerful strategy for the construction of valuable molecules from readily available materials. − In this content, alkenyl alcohols are considered as versatile substrates for these transformations. The isomerization of alkenyl alcohols to ketones through olefin migration has been catalyzed by using various metals including Pd 6 , Rh 7 , Ru 8 , and Fe 9 .…”

Rh‐Catalyzed Coupling of Aldehydes with Allylboronates Enables Facile Access to Ketones

“…Recently, we have developed a Rh‐catalyzed remote isomerization of alkenyl alcohols for the preparation of ketones, in which homoallylic alcohols are competent substrates to furnish the desired ketones in high efficiency [6] . Given that the homoallylic alcohols can be readily synthesized via the allylation of aldehydes with allylic boronic esters via a chair like transition state [7] and our group's interest in organoboron chemistry and Rh‐catalyzed transformations, we envisioned here a unique strategy for the formation of ketones via the allylation of aldehydes and subsequent chain‐walking of homoallylic alcohols (Figure 1c).…”