Synthesis of 1,3‐Dioxan‐2‐ones by Photo‐Aerobic Selenium‐π‐Acid Multicatalysis

Abstract

In memory of Professor Klaus HafnerAn expedient method for the synthesis of cyclic carbonates from homoallylic carbonic acid esters by means of photoaerobic selenium-π-acid multicatalysis is reported. Until now, conceptually related methods commonly relied either on the stoichiometric addition of electrophiles onto the substrate's alkene moiety or the presence of pre-installed leaving groups in allylic position of said alkene to -in part, catalytically -initiate an intramolecular attack by an adjacent carbonic acid ester group. In sharp contrast, the current study shows that the CÀ C double bond of homoallylic carbonic acid esters can be directly activated by the catalytic interplay of a pyrylium dye and a diselane using ambient air as the sole oxidant and visible light as an energy source.

Intermolecular Aza-Wacker Coupling of Alkenes with Azoles by Photo-Aerobic Selenium-π-Acid Multicatalysis

“…As anticipated, the yields of azole coupling products 3ak - aq are on average 23 percentage points lower (34–56%) compared to the 3z - aj series, even with the addition of cocatalyst (4-ClPhS) 2 . This observation correlates well with several mechanistic studies from our laboratories, which suggest that either the final step in the multicatalytic cycle, i.e., the β-elimination of the product from the selenium catalyst, 15 , 19 or the preceding photooxidation of the selenium residue 15b can be rate limiting. The missing electronic influence of any electron-withdrawing groups (EWG) in the case of nonpolar alkenes 2ak - 2ao is suspected to slow down β-elimination considerably, opening pathways for probably yield-diminishing side reactions such as the Schenck-ene oxidation.…”

“…The missing electronic influence of any electron-withdrawing groups (EWG) in the case of nonpolar alkenes 2ak - 2ao is suspected to slow down β-elimination considerably, opening pathways for probably yield-diminishing side reactions such as the Schenck-ene oxidation. 15 , 20 Notably, the current method shows significant preference for the formation of Markovnikov products, 21 which complements existing protocols on photoredox catalytic amination reactions of nonpolar alkenes proceeding through radical ionic π-bond activations, as they typically result in preferential formation of anti -Markovnikov regioisomers ( Scheme 1 a, path d). 5e , 7 …”

“…The abovementioned state of affairs in selenium-π-acid catalysis already indicates that its synthetic potential is far from being exhaustively exploited. For instance, our group has previously shown that the scope of suitable nucleophiles can be markedly enhanced when resorting to ambient air as a mild and compatible terminal oxidant . The implementation of air as a reactant was accomplished by the merger of photoredox and selenium-π-acid catalysis, enabling the coupling of various nucleophiles such as carboxylic acids, , hydrogen phosphates, alcohols, and sulfonamides , to simple alkenes through a dual catalytic radical-polar crossover mechanism .…”

“…For instance, our group has previously shown that the scope of suitable nucleophiles can be markedly enhanced when resorting to ambient air as a mild and compatible terminal oxidant. 15 The implementation of air as a reactant was accomplished by the merger of photoredox and selenium-π-acid catalysis, enabling the coupling of various nucleophiles such as carboxylic acids, 15a , 15b hydrogen phosphates, 15c alcohols, 15d and sulfonamides 15f , 15g to simple alkenes through a dual catalytic radical-polar crossover mechanism. 16 Against this background, we posited that this technique might also prove suitable for azole nucleophiles, provided that the envisioned heteroarenes would exhibit sufficient compatibility with our photoaerobic reaction conditions.…”

Recent Advances in the Use of Diorganyl Diselenides as Versatile Catalysts

“…Intermediate X undergoes anodic oxidation to regenerate electrophilic phenyl selenium species II and III for a new cycle (Scheme 23). More recently, in 2023, Breder and his research group [38] described the advances in the use of photo-aerobic selenium-π-acid multicatalysis in the synthesis of cyclic carbonate 24. The method was developed through the reaction of non-activated homoallylic carbonate ester 23 under ambient air as the terminal oxidant, using visible light as an energy source (Scheme 24).…”