Photocatalytic Biheterocyclization of 1,7-Diynes for Accessing Skeletally Diverse Tricyclic 2-Pyranones

Abstract

A new and green route to skeletally diverse oxo-heterocyclic architectures such as pyrano­[3,4-c]­chromen-2-ones and pyrano­[3,4-c]­quinolin-2-ones is reported via an unprecedented photocatalytic Kharasch-type cyclization/1,5-(SN″)-substitution/elimination/6π-electrocyclization/double nucleophilic substitution cascade starting from easily available heteroatom-linked 1,7-diynes and low-cost CBrCl3. During this reaction process, the full scission of carbon–halogen bonds of BrCCl3 was realized to directly build two new rings, including a lactone scaffold, using H2O as the oxygen source of the ester group.

Photocatalytic Chemodivergent Synthesis of α‐gem‐Dihalovinyl Ketones and Chromen‐2‐Ones from Monoalkynes

“…Moreover, the visible‐light‐induced Kharasch‐type addition enables a facile and atom‐economic approach to produce polyhalogenated compounds under sustainable conditions, [10] which provides excellent opportunities for late‐stage modifications via modern cross‐coupling reactions [11] . For instance, we recently reported a photocatalytic Kharasch‐type addition‐bicyclization of aromatic 1,7‐diynes with CBrCl 3 , leading to the regioselective formation of skeletally diverse tricyclic oxo ‐heterocycles, in which both CBrCl 3 and H 2 O are the source of the lactone (Scheme 1b) [10f] . Despite great advances have been achieved in this field, development of a new photocatalytic Kharasch‐type addition toward valuable functional molecules associated with safety, cost and environmental aspects is of highly desired targets in both academia and industry.…”

“…We started this study by subjecting phenylacetylene ( 1 a ) as an monoalkyne to the reactions with CBrCl 3 ( 2 a ) in the presence of fac ‐Ir(ppy) 3 under blue LED irradiation as described in our previous report [10f] (Table 1, entry 1). The reaction proceeded in a mixed solvent of ethanol/water (v/v=4:1) at room temperature under an argon atmosphere through Kharasch‐type addition and allylic substitution cascade, furnishing α ‐ gem ‐dihalovinyl ketone product 3 a in 72% yield.…”

Activation of C–Br Bond of CBr4 and CBrCl3 Using 9-Mesityl-10-methylacridinium Perchlorate Photocatalyst

“…In both cases, triethylamine was used as the electron transfer agent. To the best of our knowledge, scanty literature is available on the homolytic bond dissociation of the aliphatic C–Br bond using visible light. − The C–Br bond dissociation energy of CBr 4 is 235 kJ mol –1 (Figure a).…”

Synthesis of O-Heterocycle Spiro-Fused Cyclopentaquinolinones and Cyclopentaindenes through Visible Light-Induced Radical Cyclization Reactions

“…Due to their importance, a number of methods for the preparation of cyclopentaquinoline derivatives have been developed. , While these literature methods are generally reliable, some of them suffer from limitations such as harsh reaction conditions and low atom-economy. Therefore, how to rapidly and atom-economically synthesize cyclopentaquinoline derivatives under mild reaction conditions still remains as a challenging task . On the other hand, numerous substances essential for life activities, such as sugars, vitamins, and hormones, comprise at least one O -heterocyclic moiety .…”