Visible Light Photocatalytic Reduction of O‐Thiocarbamates: Development of a Tin‐Free Barton–McCombie Deoxygenation Reaction

Abstract

The Barton-McCombie deoxygenation is one of the most important transformations in the toolbox of organic chemists which has been the subject of a number of methodological developments. In this study, we report a photocatalyzed redox deoxygenation of secondary and tertiary alcohols from thiocarbamate precursors under visible light activation. The iridium complex IrA C H T U N G T R E N N U N G (ppy) 3 proved to be the most efficient catalyst in the presence of Hünigs base as sacrifial electron donor. A mechanistic investigation is presented based on fluorescence quenching experiments and cyclic voltammetry.

Visible‐Light Photocatalysis as an Enabling Tool for the Functionalization of Unactivated C(sp3)‐Substrates

“…In response to these issues, the groups of Goddard, Fensterbank, and Ollivier devised a visible-light-mediated and tin-free alternative strategy (Scheme 33). [80] Through the use of the reductive substrate activation mode induced by SET from the excited-state Ir III * catalyst, and DIPEA as an electron and hydrogen donor, a range of secondary alcohols were efficiently deoxygenated under the reaction conditions. Following on from their earlier work on N-(acyloxy)phthalimides (see Scheme 2), Overman and co-workers developed a method to exploit tertiary alcohols as radical precursors through the intermediacy of N-phthalimidoyl oxalates 55.…”

ChemInform Abstract: Ruthenium‐Catalyzed O‐ to S‐Alkyl Migration: A Pseudoreversible Barton—McCombie Pathway.

“…[14] Analysis of the ruthenium-catalyzed O-t oS-alkyl migration by DFT (see the Supporting Information (SI) for details) supports the proposed reaction proceeding through radical adducts (Scheme 7). As with previous reported works,adistribution of products was observed, including the radical desulfurization product (6c,4 %).…”

“…Interestingly,b oth secondary and primary rearrangement products (6a and 6b)w ere observed in a3 :1 ratio,w ell within the ratios observed for classical radical-promoted rearrangements.T he observed consistencies would strongly suggest that the presented rutheniumcatalyzed system is capable of proceeding through as imilar radical-promoted reaction pathway. [14] Analysis of the ruthenium-catalyzed O-t oS-alkyl migration by DFT (see the Supporting Information (SI) for details) supports the proposed reaction proceeding through radical adducts (Scheme 7).…”

Ruthenium‐Catalyzed O‐ to S‐Alkyl Migration: A Pseudoreversible Barton–McCombie Pathway

“…Interestingly, both secondary and primary rearrangement products ( 6 a and 6 b ) were observed in a 3:1 ratio, well within the ratios observed for classical radical‐promoted rearrangements. The observed consistencies would strongly suggest that the presented ruthenium‐catalyzed system is capable of proceeding through a similar radical‐promoted reaction pathway 14…”