Teaching Aldehydes New Tricks Using Rhodium- and Cobalt-Hydride Catalysis

Abstract

Conspectus By using transition metal catalysts, chemists have altered the “logic of chemical synthesis” by enabling the functionalization of carbon–hydrogen bonds, which have traditionally been considered inert. Within this framework, our laboratory has been fascinated by the potential for aldehyde C–H bond activation. Our approach focused on generating acyl-metal-hydrides by oxidative addition of the formyl C–H bond, which is an elementary step first validated by Tsuji in 1965. In this Account, we review our efforts to overcome limitations in hydroacylation. Initial studies resulted in new variants of hydroacylation and ultimately spurred the development of related transformations (e.g., carboacylation, cycloisomerization, and transfer hydroformylation). Sakai and co-workers demonstrated the first hydroacylation of olefins when they reported that 4-pentenals cyclized to cyclopentanones, using stoichiometric amounts of Wilkinson’s catalyst. This discovery sparked significant interest in hydroacylation, especially for the enantioselective and catalytic construction of cyclopentanones. Our research focused on expanding the asymmetric variants to access medium-sized rings (e.g., seven- and eight-membered rings). In addition, we achieved selective intermolecular couplings by incorporating directing groups onto the olefin partner. Along the way, we identified Rh and Co catalysts that transform dienyl aldehydes into a variety of unique carbocycles, such as cyclopentanones, bicyclic ketones, cyclohexenyl aldehydes, and cyclobutanones. Building on the insights gained from olefin hydroacylation, we demonstrated the first highly enantioselective hydroacylation of carbonyls. For example, we demonstrated that ketoaldehydes can cyclize to form lactones with high regio- and enantioselectivity. Following these reports, we reported the first intermolecular example that occurs with high stereocontrol. Ketoamides undergo intermolecular carbonyl hydroacylation to furnish α-acyloxyamides that contain a depsipeptide linkage. Finally, we describe how the key acyl-metal-hydride species can be diverted to achieve a C–C bond-cleaving process. Transfer hydroformylation enables the preparation of olefins from aldehydes by a dehomologation mechanism. Release of ring strain in the olefin acceptor offers a driving force for the isodesmic transfer of CO and H2. Mechanistic studies suggest that the counterion serves as a proton-shuttle to enable transfer hydroformylation. Collectively, our studies showcase how transition metal catalysis can transform a common functional group, in this case aldehydes, into structurally distinct motifs. Fine-tuning the coordination sphere of an acyl-metal-hydride species can promote C–C and C–O bond-forming reactions, as well as C–C bond-cleaving processes.

Catalytic asymmetric hydrometallation of cyclobutenes with salicylaldehydes

“…23 While intramolecular hydroacylation reactions are well established, the intermolecular Rh-catalysed hydroacylation is oen associated with an undesired reductive decarbonylation, and many specic solutions for this problem involving chelating groups have been developed. 23 The use of ortho-hydroxybenzaldehydes (salicylaldehydes) represents one of the strategies and several useful asymmetric hydroacylations with terminal alkenes have been reported. [24][25][26] Internal alkenes represent signicantly more challenging substrates in Rh-catalysed intermolecular hydroacylations, but a few reactions between norbornadienes or cyclopropenes and salicylaldehydes have been reported by the groups of Bolm and Dong, which are likely driven by the release of olenic-strain.…”

“…Metal-catalysed hydroacylation, 22 and especially Rh-catalysed hydroacylation reactions between alkenes and aldehydes are powerful tools for the synthesis of ketones and operate via a hydrometallation mechanism. 23 While intramolecular hydroacylation reactions are well established, the intermolecular Rh-catalysed hydroacylation is often associated with an undesired reductive decarbonylation, and many specific solutions for this problem involving chelating groups have been developed. 23 The use of ortho -hydroxybenzaldehydes (salicylaldehydes) represents one of the strategies and several useful asymmetric hydroacylations with terminal alkenes have been reported.…”

Azine-N-oxides as effective controlling groups for Rh-catalysed intermolecular alkyne hydroacylation

“…The success of Shibata's chemistry prompted us to consider the use of N-oxides in intermolecular hydroacylation. 15 Azine aldehydes are challenging substrates in hydroacylation as the pyridyl nitrogen can prevent the formation of chelated rhodacycle intermediates, which are key for reaction progression in many hydroacylation systems. 16,17 Catalyst inhibition can also be problematic.…”

Rhodium and Iridium Mediated C-H and O-H Bond Activation of Two Schiff Base Ligands: Synthesis, Characterization and Catalytic Properties of the Organometallic Complexes

“…The chemistry of rhodium and iridium has been receiving considerable current attention ( Chi et al, 2017 ; Colombo et al, 2020 ; Mao et al, 2020 ; Shaikh et al, 2020 ; Alsalahi and Trzeciak, 2021 ; Davison et al, 2021 ; Monti et al, 2021 ; Vuuren et al, 2021 ), largely because of the interesting properties exhibited by the complexes of these metals. As properties of the complexes are dictated primarily by the coordination environment around the metal center, complexation of rhodium by ligands of selected types has been of significant importance, and the present work has originated from our interest in this area ( Dutta et al, 2000a ; Dutta et al, 2000b ; Das et al, 2002 ; Dutta et al, 2002 ; Acharyya et al, 2004a ; Acharyya et al, 2004b ; Acharyya et al, 2005 ; Acharyya et al, 2006 ; Basu et al, 2006 ; Baksi et al, 2007a ; Basu et al, 2007 ; Baksi et al, 2007b ; Dasgupta et al, 2008 ; GuhaRoy et al, 2008 ; Acharyya et al, 2009 ; GuhaRoy et al, 2009 ; Baksi et al, 2010 ; Basu et al, 2010 ; Majumder et al, 2011 ; Seth and Bhattacharya, 2011 ; Bhattacharya et al, 2012 ; Paul and Bhattacharya, 2012 ; Sengupta and Bhattacharya, 2013 ; Paul et al, 2014 ).…”