Visible-light-mediated defluorinative cyclization of α-fluoro-β-enamino esters catalyzed by 4-CzIPN

Abstract

Using 4-CzIPN as an energy transfer (EnT) photocatalyst and α-fluoro-β-enamino esters as the substrates, a mild 6π-photocyclization/defluorination of N-aryl enamines was carried out to efficiently construct indoles without oxidant and...

Visible-Light-Mediated Energy Transfer Enables Cyclopropanes Bearing Contiguous All-Carbon Quaternary Centers

“…To verify our hypothesis, we explored cyclopropanation using N -tosylhydrazone 1a and 1,1-diphenylethylene 1b as model substrates. To our delight, the corresponding cyclopropane bearing two quaternary centers was successfully synthesized in our initial attempts using different photosensitizers, which showed that 2,4,5,6-tetra­(carbazol-9-yl)­benzene-1,3-dicarbonitrile (4-CzIPN), with a triplet energy of 60.0 kcal/mol, is the most suitable photosensitizer (Table , entries 1–6). Other photosensitizers, including Eosin Y (43.5 kcal/mol), Ir­[(dtbbpy)­(ppy) 2 ]­PF 6 (49.2 kcal/mol), fac -Ir­(ppy) 3 (57.8 kcal/mol), and Ir­( p -F-ppy) 3 (58.6 kcal/mol), exhibited lower reactivity, presumably because they possess lower triplet energy than that of 4-CzIPN.…”

Synthesis of Chiral α‐Amino Ketones via Transition Metal Catalyzed or Photoredox Cross‐Coupling and Olefin Photo‐Cleavage Reaction Sequence

“…[37] The observed photoinduced E!Z isomerization of cinnamyl systems is a well-known process. [38][39][40][41][42][43][44] For example, Stephenson and co-workers [39] exposed (E)-2iodo-cinnamyl alcohol to standard reaction conditions with Ir(ppy) 3 and observed efficient dehalogenation, although the reduced allylic alcohol consisted of a mixture of E:Z isomers with a photostationary compo- sition (Z:E) of 3.5:1. They verified the existence of an energy transfer pathway by exposing trans-cinnamyl alcohol to the Ir photocatalyst, which yielded comparable results.…”

“…The observed photoinduced E→Z isomerization of cinnamyl systems is a well‐known process [38–44] . For example, Stephenson and co‐workers [39] exposed ( E )‐2‐iodo‐cinnamyl alcohol to standard reaction conditions with Ir(ppy) 3 and observed efficient dehalogenation, although the reduced allylic alcohol consisted of a mixture of E : Z isomers with a photostationary composition ( Z : E ) of 3.5:1.…”

“…[40] Such isomerization can be promoted also by organic dyes like 4CzIPN, e. g., during the synthesis of allylamines via photocatalyzed decarboxylative radical addition to 2-bromostyrenes [41] or with decarboxylative hydroalkylation alkynes. [42] The 4CzIPN photocatalyst not only outperforms SET but can also mediated a singlet-to-triplet interconversion and can act in the energy transfer process (E nT ) (E T = 56.4 kcal/mol) [43] where it is responsible for the olefin isomerization which provides contra-thermodynamic isomers. [43] To assess whether the photocatalyst plays a role in the isomerization process, we took (E)-olefin (E)-7 a, prepared via Suzuki reaction, and exposed it to blue LED light (2 × 36 W, 460-465 nm) for the cross-coupling reaction (see ESI).…”

“…[42] The 4CzIPN photocatalyst not only outperforms SET but can also mediated a singlet-to-triplet interconversion and can act in the energy transfer process (E nT ) (E T = 56.4 kcal/mol) [43] where it is responsible for the olefin isomerization which provides contra-thermodynamic isomers. [43] To assess whether the photocatalyst plays a role in the isomerization process, we took (E)-olefin (E)-7 a, prepared via Suzuki reaction, and exposed it to blue LED light (2 × 36 W, 460-465 nm) for the cross-coupling reaction (see ESI). The isomerization was monitored by NMR and showed that the amount of Z-isomers increased with increasing the exposure time to blue light (see Supporting materials for more details).…”