The photoenol tautomer of 5‐methyl‐1, 4‐naphthoquinone

Abstract

SummaryIrradiation of pale yellow 5-methyl-l,4-naphthoquinone (1, Scheme I ) yields the blue photoenol 4-hydroxy-5-methylidene-1(5 H)-naphthalenone (2) which is stable at 77 K, At room temperature the enol retautomerizes to starting material, the reaction rate being strongly dependent on the hydrogen-bond-acceptor basicity of the solvent. The enol is trapped in the presence of acid by protonation at the remaining carbonyl oxygen atom and subsequent electrophilic reaction of the exocyclic methylene group.

Kinon-metidi (II. dio): Fotokemijsko generiranje i razvoj primjene u fotokemoterapiji

“…su 1977. objavili prvi primjer fotokemijskog generiranja QM-a reakcijom fototautomerizacije u naftokinonu 93. 52 Reakcija se odvija preko tripletnog pobuđenog stanja, gdje dolazi do enolizacije i nastanka QM-a 94 (shema 17). Rokita je taj tip reakcije upotrijebio za generiranje QM-a iz antrakinon-oligonukleotidnog konjugata 95 (slika 11), koji je upotrijebio za križno povezivanje molekule DNA na vrlo specifičnom dijelu, komplementarnom s faktorom prepoznavanja u derivatu 95.…”

Photoinduced Cyclization of (o‐Alkylbenzoyl)phosphonates to Benzocyclobutenols

“…[3] Upon excitation, intramolecular hydrogen transfer (C(sp 3 )-H to O-H) occurs with 1 to generate biradical 2.I ti somerizes into o-quinodimethane 3, [4,5] which has ac losed-shellc onfiguration but lacks aromaticity.T here are two stereoisomers 3a and 3b possibly generated from 2.T wo pathways are subsequently available for the dienes 3a and 3b.O ne is ap rotont ransfer pathway reverting to 1 [6] and the other is a4 p electrocyclic ring-closing pathway to benzocyclobutenol 4.I nt he case of 3a,a ni ntramolecular 1,5-proton transfer reaction is so much faster than Scheme1.Photocyclization of o-alkylphenyl ketones.[a] Dr. The remarkable efficiency is ascribed to the electron-accepting character of the phosphonate substituent, which facilitates thermal ring closing of the o-quinodimethane intermediate and suppresses reversion to the startingc arbonyl compound.…”

“…[3] Upon excitation, intramolecular hydrogen transfer (C(sp 3 )-H to O-H) occurs with 1 to generate biradical 2.I ti somerizes into o-quinodimethane 3, [4,5] which has ac losed-shellc onfiguration but lacks aromaticity.T here are two stereoisomers 3a and 3b possibly generated from 2.T wo pathways are subsequently available for the dienes 3a and 3b.O ne is ap rotont ransfer pathway reverting to 1 [6] and the other is a4 p electrocyclic ring-closing pathway to benzocyclobutenol 4.I nt he case of 3a,a ni ntramolecular 1,5-proton transfer reaction is so much faster than Scheme1.Photocyclization of o-alkylphenyl ketones. [3] Upon excitation, intramolecular hydrogen transfer (C(sp 3 )-H to O-H) occurs with 1 to generate biradical 2.I ti somerizes into o-quinodimethane 3, [4,5] which has ac losed-shellc onfiguration but lacks aromaticity.T here are two stereoisomers 3a and 3b possibly generated from 2.T wo pathways are subsequently available for the dienes 3a and 3b.O ne is ap rotont ransfer pathway reverting to 1 [6] and the other is a4 p electrocyclic ring-closing pathway to benzocyclobutenol 4.I nt he case of 3a,a ni ntramolecular 1,5-proton transfer reaction is so much faster than Scheme1.Photocyclization of o-alkylphenyl ketones.…”

“…Since the photoreaction is operationally simple and tolerant to various functional groups, the present approach would come into use for further derivatization of synthetic purposes.The mechanism of the photocyclization of o-alkylphenylk etones has been studied intensively (Scheme1). [3] Upon excitation, intramolecular hydrogen transfer (C(sp 3 )-H to O-H) occurs with 1 to generate biradical 2.I ti somerizes into o-quinodimethane 3, [4,5] which has ac losed-shellc onfiguration but lacks aromaticity.T here are two stereoisomers 3a and 3b possibly generated from 2.T wo pathways are subsequently available for the dienes 3a and 3b.O ne is ap rotont ransfer pathway reverting to 1 [6] and the other is a4 p electrocyclic ring-closing pathway to benzocyclobutenol 4.I nt he case of 3a,a ni ntramolecular 1,5-proton transfer reaction is so much faster than Scheme1.Photocyclization of o-alkylphenyl ketones.[a] Dr.…”

“…Cyclic ester 5falso afforded the benzocyclobutenol 7f (87 %, entry 4). Various functional groups like methoxy,t rifluoromethyl, bromo, and carbamate groups werea llowed on the aromaticr ing to give the benzocyclobutenols 7g-j in yields ranging from 74 to 89 %( entries [5][6][7][8]. Ar eaction of 5k having a3 -methoxypropyl substituent at the o-position gave the cis-isomer 7k exclusively (entry 9).…”