Beckmann Fission of Some Fused Cyclobutanones: A New Entry into Indole-2-Acetonitriles and Benzo[<u>b</u>]thiophene-2-acetonitrile

Ikeda, Masazumi; Uno, Toshiko; Homma, Koichi; Ohno, Katsuhito; Tamura, Yasumitsu

doi:10.1080/00397918008064266

Cited by 20 publications

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“…The [2+2] photocycloaddition between 1-acylindoles and substituted ethenes is known to proceed under the sensitization of acetophenone with Pyrex-filtered irradiation (>300 nm) to yield cyclobutane-fused indolines, though reactions with 1-aroylindoles can be performed without the sensitizer . However, the reactions required large excesses of alkenes to obtain acceptable yields of the products in many cases, and the regioselectivity, namely, head-to-head or head-to-tail selectivity, depended on the electronic properties of the alkenes employed. , To overcome this problem, intramolecular cycloadditions were investigated by tethering the alkene to the acyl substituent of the indoles. This strategy gave the [2+2] adducts regio- and stereoselectively, while the resulting cyclobutane ring did not have any functional groups that were useful for further molecular transformation …”

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Stereoselective Construction of Methylenecyclobutane-Fused Indolines through Photosensitized [2+2] Cycloaddition of Allene-Tethered Indole Derivatives

Arai

Ohkuma

2019

Org. Lett.

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Irradiation of 1-(hexa-4,5-dienoyl)indole derivatives in the presence of an aromatic ketone by a high-pressure mercury lamp through Pyrex glass gave the corresponding cyclized products stereoselectively in high yields. The major part of the products was an all-cis-fused methylenecyclobutane-type compound produced through [2+2] cycloaddition, accompanied by small amounts of alkynes via 1,5-hydrogen transfer of a biradical intermediate. Among a range of aromatic ketones, 3′,4′dimethoxyacetophenone was found to sensitize the substrate quite effectively.

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“…To date, a number of synthetic methods have been reported for this important class of compounds, whereas there has been much less exploration of cyclobutane-fused indolines. , The [2+2] photocycloaddition using 1-acylindoles as components is an exception. It has been extensively examined to access the cyclobutane-fused compounds. − …”

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confidence: 99%

Stereoselective Construction of Methylenecyclobutane-Fused Indolines through Photosensitized [2+2] Cycloaddition of Allene-Tethered Indole Derivatives

Arai

Ohkuma

2019

Org. Lett.

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“…The simplest mechanism for the conversion of oximes 5 and 6 into the heteroaromatic products 7 , 8 , and 10 would appear to involve initial ketoxime fragmentation of the abnormal (second-order) Beckmann type, presumably induced by S 2 Cl 2 and/or catalyzed by traces of SCl 2 . The cyclobutane ring opening processes for the two oxime isomers would give the isomeric nitriles 21 (Scheme ) and 23 (Scheme ). The former could react with S 2 Cl 2 to give the dithiole ring, which by chlorination and dehydrochlorination could give the unsaturated system 22 , which can be fully chlorinated by S 2 Cl 2 and NCS in the carbocyclic ring; all positions of this ring are activated by electron release from the dithiole sulfur atoms, exactly as proposed 6 for the formation of 1 and 2 above.…”

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Cyclopenta-1,2-dithioles, Cyclopenta-1,2-thiazines, and Methylenoindenes from New Molecular Rearrangements

et al. 1996

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The cyclobutanone oxime 6 reacts with disulfur dichloride, N-chlorosuccinimide, and Hü nig's base to give three unexpected 10 π pseudoazulenes in low yield: the dark blue cyclopenta-1,2-dithiole 7, its red isomer 10, and the orange cyclopenta-1,2-thiazine 8. The benzo derivative 14 of oxime 6 gives an analogous benzo product 15 together with the methylenoindene 16 in high yield. The formation of all of these products can be explained by a unified mechanism based on initial abnormal Beckmann rearrangement of the oximes to cyanides followed by cyclization and/or exhaustive chlorination and dehydrochlorination. The 1,2-dithiole 7 is synthesized independently from 1-(cyanomethyl)cyclopentene 11 and the above reagents, and 1-cyanomethylindene 17 is similarly converted into methylenoindenes 18 and 19, which are isomers of product 16. Structures 7 and 15 are confirmed by X-ray crystallography, and compounds 7, 8, 15, 16, 18, and 19 show birefringence on heating in a hot stage polarizing microscope indicating, most unexpectedly, liquid crystalline behavior.

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TheBeckmann Reactions: Rearrangements, Elimination–Additions, Fragmentations, and Rearrangement–Cyclizations

Gawley

1988

Organic Reactions

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The Beckmann rearrangement, the acid‐mediated isomerization of oximes to amides, was discovered by Beckmann in 1886. As one of the oldest and most familiar transformations in organic chemistry, it has been reviewed several times. What has become known as the Beckmann fragmentation was in fact first observed by Wallach in 1889 but was not developed extensively until the 1960s. It has been referred to by several names over the years and has also been reviewed. The rearrangement cyclization is the intramolecular cyclization of a nitrilium ion generated by Beckmann rearrangement from an oxime. Within the context of an aromatic terminator, the process was first reported by Goldschmidt in 1895. Wallach reported the first case of an aliphatic terminator in 1901, although the reported structure was incorrect, and Perkin was apparently the first to observe a heteroatom terminator, but he also reported an incorrect structure. The process has been exploited only quite recently. This chapter is an update of these reactions, last reviewed in this series in 1960. Not covered are transformations that have been labeled Beckmann‐type reactions but are mechanistically unrelated. The most prominent of these is the so‐called photochemical Beckmann rearrangement, first observed by De Mayo in 1963 and discussed in a review several years ago. Worthy of mention, however, is the fact that many oximes that suffer fragmentation under acidic conditions undergo rearrangement when photolyzed. Throughout this chapter, the ( E ) and ( Z ) nomenclature is used to describe oxime geometry.

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Beckmann Fission of Some Fused Cyclobutanones: A New Entry into Indole-2-Acetonitriles and Benzo[b]thiophene-2-acetonitrile

Cited by 20 publications

References 5 publications

Stereoselective Construction of Methylenecyclobutane-Fused Indolines through Photosensitized [2+2] Cycloaddition of Allene-Tethered Indole Derivatives

Stereoselective Construction of Methylenecyclobutane-Fused Indolines through Photosensitized [2+2] Cycloaddition of Allene-Tethered Indole Derivatives

Cyclopenta-1,2-dithioles, Cyclopenta-1,2-thiazines, and Methylenoindenes from New Molecular Rearrangements

TheBeckmann Reactions: Rearrangements, Elimination–Additions, Fragmentations, and Rearrangement–Cyclizations

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