Formation of anti‐Bredt‐type azabicyclo[4.2.0]octene frameworks through photochemical intramolecular [2+2] cycloaddition between indole and a distal double bond of allene

Abstract

Irradiation of 1‐(penta‐3,4‐dienoyl)indole derivatives in the presence of an aromatic ketone by a high‐pressure mercury lamp through Pyrex glass gave two types of cyclized products stereoselectively in high combined yields. The major product was a tetracyclic indoline derivative containing anti‐Bredt‐type azabicyclo[4.2.0]octene moiety produced via photo [2+2] cycloaddition between indole and a distal double bond of allene, accompanied by a small amount of proximal [2+2] adduct. Among a range of aromatic ketones screened, 3′,4′‐methylenedioxyacetophenone was found to sensitize the substrate most effectively.

Light‐Driven [2 + 2] Cycloaddition Strategies for the Synthesis of Cyclobuta[ b ]indoles and Their Derivatives

“…The formation of a C─C bond between the C2 position of the indole and the alkene moiety is followed by ISC, generating an open-shell singlet 1,4-diradical intermediate II. This intermediate undergoes radical-radical recombination to furnish the cyclobutane-fused product 75.Arai[99] investigated the formation of anti-Bredt-type azabicyclo[4.2.0]octene scaffolds through photoinduced intramolecular [2 + 2] cycloaddition, irradiating 1-(penta-3,4-dienoyl)indole derivatives 76 using a high-pressure mercury lamp and methylenedioxy acetophenone as PS. In this process, two different tetracyclic indoline derivatives, 77a and 78a, were generated along the photocyclization process with the predominant formation of the compound 77.…”

“…The formation of a C─C bond between the C2 position of the indole and the alkene moiety is followed by ISC, generating an open-shell singlet 1,4-diradical intermediate II. This intermediate undergoes radical-radical recombination to furnish the cyclobutane-fused product 75.Arai[99]…”

“…Arai [99] investigated the formation of anti ‐Bredt‐type azabicyclo[4.2.0]octene scaffolds through photoinduced intramolecular [2 + 2] cycloaddition, irradiating 1‐(penta‐3,4‐dienoyl)indole derivatives 76 using a high‐pressure mercury lamp and methylenedioxy acetophenone as PS. In this process, two different tetracyclic indoline derivatives, 77a and 78a , were generated along the photocyclization process with the predominant formation of the compound 77 .…”

Light‐Driven [2 + 2] Cycloaddition Strategies for the Synthesis of Cyclobuta[ b ]indoles and Their Derivatives

“…The formation of a C─C bond between the C2 position of the indole and the alkene moiety is followed by ISC, generating an open-shell singlet 1,4-diradical intermediate II. This intermediate undergoes radical-radical recombination to furnish the cyclobutane-fused product 75.Arai[99] investigated the formation of anti-Bredt-type azabicyclo[4.2.0]octene scaffolds through photoinduced intramolecular [2 + 2] cycloaddition, irradiating 1-(penta-3,4-dienoyl)indole derivatives 76 using a high-pressure mercury lamp and methylenedioxy acetophenone as PS. In this process, two different tetracyclic indoline derivatives, 77a and 78a, were generated along the photocyclization process with the predominant formation of the compound 77.…”

“…The formation of a C─C bond between the C2 position of the indole and the alkene moiety is followed by ISC, generating an open-shell singlet 1,4-diradical intermediate II. This intermediate undergoes radical-radical recombination to furnish the cyclobutane-fused product 75.Arai[99]…”

“…Arai [99] investigated the formation of anti ‐Bredt‐type azabicyclo[4.2.0]octene scaffolds through photoinduced intramolecular [2 + 2] cycloaddition, irradiating 1‐(penta‐3,4‐dienoyl)indole derivatives 76 using a high‐pressure mercury lamp and methylenedioxy acetophenone as PS. In this process, two different tetracyclic indoline derivatives, 77a and 78a , were generated along the photocyclization process with the predominant formation of the compound 77 .…”

Thermally-induced intramolecular [2 + 2] cycloaddition of allene-methylenecyclopropanes: expedient access to two separable spiropolycyclic heterocycles

“…Cyclobutane, as a special strained structure, exists in many natural products and pharmaceutical molecules. 1 In general, [2 + 2] cycloaddition is an extremely effective method for the construction of cyclobutane structural motifs 2,3 and it is regarded as a key step in the synthesis of many natural products and so on. 4 In addition, [2 + 2] cycloaddition reactions, which do not produce any waste, have attracted great attention from chemists in recent years as an ideal process in terms of atom economy.…”

Light‐Driven [2 + 2] Cycloaddition Strategies for the Synthesis of Cyclobuta[ b ]indoles and Their Derivatives

“…The formation of a C─C bond between the C2 position of the indole and the alkene moiety is followed by ISC, generating an open-shell singlet 1,4-diradical intermediate II. This intermediate undergoes radical-radical recombination to furnish the cyclobutane-fused product 75.Arai[99] investigated the formation of anti-Bredt-type azabicyclo[4.2.0]octene scaffolds through photoinduced intramolecular [2 + 2] cycloaddition, irradiating 1-(penta-3,4-dienoyl)indole derivatives 76 using a high-pressure mercury lamp and methylenedioxy acetophenone as PS. In this process, two different tetracyclic indoline derivatives, 77a and 78a, were generated along the photocyclization process with the predominant formation of the compound 77.…”

“…The formation of a C─C bond between the C2 position of the indole and the alkene moiety is followed by ISC, generating an open-shell singlet 1,4-diradical intermediate II. This intermediate undergoes radical-radical recombination to furnish the cyclobutane-fused product 75.Arai[99]…”

“…Arai [99] investigated the formation of anti ‐Bredt‐type azabicyclo[4.2.0]octene scaffolds through photoinduced intramolecular [2 + 2] cycloaddition, irradiating 1‐(penta‐3,4‐dienoyl)indole derivatives 76 using a high‐pressure mercury lamp and methylenedioxy acetophenone as PS. In this process, two different tetracyclic indoline derivatives, 77a and 78a , were generated along the photocyclization process with the predominant formation of the compound 77 .…”

Thermally-induced intramolecular [2 + 2] cycloaddition of allene-methylenecyclopropanes: expedient access to two separable spiropolycyclic heterocycles

“…Cyclobutane, as a special strained structure, exists in many natural products and pharmaceutical molecules. 1 In general, [2 + 2] cycloaddition is an extremely effective method for the construction of cyclobutane structural motifs 2,3 and it is regarded as a key step in the synthesis of many natural products and so on. 4 In addition, [2 + 2] cycloaddition reactions, which do not produce any waste, have attracted great attention from chemists in recent years as an ideal process in terms of atom economy.…”

Light‐Driven [2 + 2] Cycloaddition Strategies for the Synthesis of Cyclobuta[ b ]indoles and Their Derivatives

“…The formation of a C─C bond between the C2 position of the indole and the alkene moiety is followed by ISC, generating an open-shell singlet 1,4-diradical intermediate II. This intermediate undergoes radical-radical recombination to furnish the cyclobutane-fused product 75.Arai[99] investigated the formation of anti-Bredt-type azabicyclo[4.2.0]octene scaffolds through photoinduced intramolecular [2 + 2] cycloaddition, irradiating 1-(penta-3,4-dienoyl)indole derivatives 76 using a high-pressure mercury lamp and methylenedioxy acetophenone as PS. In this process, two different tetracyclic indoline derivatives, 77a and 78a, were generated along the photocyclization process with the predominant formation of the compound 77.…”

“…The formation of a C─C bond between the C2 position of the indole and the alkene moiety is followed by ISC, generating an open-shell singlet 1,4-diradical intermediate II. This intermediate undergoes radical-radical recombination to furnish the cyclobutane-fused product 75.Arai[99]…”

“…Arai [99] investigated the formation of anti ‐Bredt‐type azabicyclo[4.2.0]octene scaffolds through photoinduced intramolecular [2 + 2] cycloaddition, irradiating 1‐(penta‐3,4‐dienoyl)indole derivatives 76 using a high‐pressure mercury lamp and methylenedioxy acetophenone as PS. In this process, two different tetracyclic indoline derivatives, 77a and 78a , were generated along the photocyclization process with the predominant formation of the compound 77 .…”

Thermally-induced intramolecular [2 + 2] cycloaddition of allene-methylenecyclopropanes: expedient access to two separable spiropolycyclic heterocycles

“…Cyclobutane, as a special strained structure, exists in many natural products and pharmaceutical molecules. 1 In general, [2 + 2] cycloaddition is an extremely effective method for the construction of cyclobutane structural motifs 2,3 and it is regarded as a key step in the synthesis of many natural products and so on. 4 In addition, [2 + 2] cycloaddition reactions, which do not produce any waste, have attracted great attention from chemists in recent years as an ideal process in terms of atom economy.…”