Photochemical Generation and the Reactivity ofo-Naphthoquinone Methides in Aqueous Solutions

Abstract

Irradiation of 3-hydroxy-2-naphthalenemethanol (3a) and 2-hydroxy-1-naphthalenemethanol (4a) results in efficient (Phi(254) = 0.17 and 0.20) dehydration and the formation of isomeric naphthoquinone methides, 2,3-naphthoquinone-3-methide (1) and 1,2-naphthoquinone-1-methide (2), respectively. In aqueous solution, naphthoquinone methides 1 and 2 undergo rapid hydration to regenerate starting materials (tau(H2O) (1) = 7.4 ms and tau(H2O) (2) = 4.5 ms at 25 degrees C). The hydration reaction is strongly catalyzed by the hydroxide ion but shows acid catalysis only at pH < 1. Reactive intermediates 1 and 2 can be intercepted by other nucleophiles, such as the azide ion (k(N3)(1) = 2.0 x 10(4) M(-1) s(-1) and k(N3)(2) = 3.0 x 10(4) M(-1) s(-1)) or thiol (k(SH)(1) = 2.2 x 10(5) M(-1) s(-1) and k(SH)(2) = 3.3 x 10(5) M(-1) s(-1)). Ethyl vinyl ether readily reacts with 1 and 2 (k(DA)(1) = 4.1 x 10(4) M(-1) s(-1) and k(DA)(2) = 6.0 x 10(4) M(-1) s(-1)) to produce Diels-Alder adducts in excellent yield. o-Naphthoquinone methides 1 and 2 were also generated by photolysis of 3-ethoxymethyl- (3b) and 1-(ethoxymethyl)-2-naphthols (4b), as well as from (2-hydroxy-3-naphthyl)methyl- (3c) and [(2-hydroxy-1-naphthyl)methyl] trimethylammonium iodides (4c). Laser flash photolysis of 3a,b and 4a,b allows the detection of short-lived (tau(25 degrees C) approximately 12 micros) precursors of naphthoquinone methides 1 and 2. On the basis of the precursor reactivity and the results of DFT calculations, 2H-naphthoxete structure was assigned to these species.

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

“…Kod terfenilnih derivata (58 i 59) primijećena je reakcija fotosolvolize, što indicira postojanje QM-a kao međuprodukta, no oni nastaju s vrlo niskim kvantnim prinosima i kratkoživući su te nisu mogli biti okarakterizirani LFP-om. 34 Popik 35 i Freccero 11a također su studirali reakciju fotodehidratacije kod naftalenskih derivata. S obzirom na to da povećani kromoforni sustav pruža mogućnosti generiranja QM-a svjetlošću valne duljine 350 nm, generiranje QM-a iz takvih derivata je od osobitog interesa za biološku primjenu QM-a.…”

“…Shema 11 -Fotodehidratacija u derivatima 2-naftola 62 i 63 35 Scheme 11 -Photodehydration in derivatives of 2-naphthol 62 and 63 U radu autori navode i potencijalnu primjenu QM-a dobivenih iz spojeva 81 i 82 u biološkim sustavima, ali iako se radi o vrlo obećavajućim spojevima, nažalost nisu provedena nikakva biološka ispitivanja. 11a i naftalena 89 11c (slika 10).…”

Near-Visible Light Generation of a Quinone Methide from 3-Hydroxymethyl-2-anthrol

“…The flask was charged with 3-bromo-2-hydroxyanthracene (6, 286 mg, 1.00 mmol) and dry Et2O (10 mL) and cooled in an ice-methanol 16 bath (-15 to -10 °C). BuLi (2.5 M in hexanes, 1.2 mL, 3.00 mmol) was added dropwise over 15 min changing the color to brown.…”

“…16 The photogeneration of naphthalene QMs was later applied to photo-caging 17 and for surface modification and photolithography. We became interested in the photochemical formation of sterically congested QMs that have potential biological applicability.…”

“…Since it is known that intramolecular H-bonding with the benzyl alcohol increases acidity in 2-naphthol, 16 the anticipated pKa values for 7 are expected to be somewhat lower.…”