Photocatalytic esterification under Mitsunobu reaction conditions mediated by flavin and visible light

Abstract

The usefulness of flavin-based aerial photooxidation in esterification under Mitsunobu reaction conditions was demonstrated, providing aerial dialkyl azodicarboxylate recycling/generation from the corresponding dialkyl hydrazine dicarboxylate. Simultaneously, activation of triphenylphosphine (PhP) by photoinduced electron transfer from flavin allows azo-reagent-free esterification. An optimized system with 3-methylriboflavin tetraacetate (10%), oxygen (terminal oxidant), visible light (450 nm), PhP, and dialkyl hydrazine dicarboxylate (10%) has been shown to provide efficient and stereoselective coupling of various alcohols and acids to esters with retention of configuration.

Flavin Photocatalysts for Visible‐Light [2+2] Cycloadditions: Structure, Reactivity and Reaction Mechanism

“…[5] Only recently,r esearch in this area has brought some fundamentala pplications of the flavins in photocatalysis, namely in the oxidation of benzylic derivatives [6] and dialkyl hydrazinedicarboxylates, [7] in sulfoxidation, [8] aromatic chlorination, [9] E/Z isomerization, [10] cycloelimination [11] and esterification. [7] However,a lmost all flavin-based photocatalytic processesu se riboflavin derivatives 1 (isoalloxazines)a lthough the other analogues, for example, alloxazines 2 or deazaflavins 3,a re known to be also photoactive. [12] Very recently,w eh ave showni ntramolecular [2+ +2] photocycloaddition mediated by 1-butyl-3-methyl-1,3-dimethoxyalloxazine (2e)a nd visible light as one of the rare examples of the photocatalytic application of a" flavin" with other than an isoalloxazine core (for the structureo ff lavins, see Figure 1).…”

“…On the other hand, though the flavins and their derivatives are involved in various photochemical processes in nature, their use in light‐dependent synthetic transformations has long been a matter of few examples . Only recently, research in this area has brought some fundamental applications of the flavins in photocatalysis, namely in the oxidation of benzylic derivatives and dialkyl hydrazinedicarboxylates, in sulfoxidation, aromatic chlorination, E / Z isomerization, cycloelimination and esterification . However, almost all flavin‐based photocatalytic processes use riboflavin derivatives 1 (isoalloxazines) although the other analogues, for example, alloxazines 2 or deazaflavins 3 , are known to be also photoactive .…”

Recent Advances in the Synthesis of Carboxylic Acid Esters

“…The catalytic activation of PPh 3 can be achieved by iron [34]. Photo-irradiated procedure in the presence of PPh 3 with a catalytic amount of flavin and azo compound under O 2 was developed [35]. XtalFluor-E and tropylium-based coupling reagents were found to be effective for the esterification [36,37].…”

The PhotoFlexys: A Multi‐Purpose Reactor Platform to Simplify Process Intensification and Mechanistic Studies in Photochemistry

“…Since the pioneering work of Stephenson, [1] Yoon [2] and MacMillan, [3] photocatalysis has become an important instrument in the toolbox of organic chemistry. [4] Employing light as an selective and readily available energy source, researchers not only developed light-driven equivalents of existing techniques [5][6][7] but also proved its potential for challenging syntheses like CÀ H activations [8][9][10] or late stage functionalization's. [10][11][12][13] With this, photocatalysis has become a promising approach for the synthesis of pharmaceutical agents.…”