1.2- Naphthoquinone 1-methide

Wan also studied hydroxybenzyl alcohols based on the naphthalene chromo-phore.40 Naphthols 50 and 51 were both examined for their ability to photogenerate naphthoquinone methides 52 and 53, respectively (Eqs. 1.12 and 1.13). While 50 underwent very efficient photosolvolysis, presumably via naphthoquinone methide 52, 51 was essentially unreactive when exposed to light. The inability of 51 to photogenerate 53 is a rare example where the generality of the photodehydration of benzyl alcohols fails. LFP of 50 yielded a very strong visible absorption (A x = 410 and 700 nm) that decayed in aqueous acetonitrile with a lifetime of 34 ps (Fig. 1.2). This transient was assigned to naphthoquinone methide 52 due in part to its efficient quenching when the nucleophilic ethanolamine was added. 

The Popik group has recently begun to explore the potential of phenols to photorelease ethers and alcohols attached to an ortho-hem,y c group. For example, they have shown that esters and ethers of (3-hydroxymethyl)naphthalene-2-ol (i.e., 70) efficiently release the corresponding alcohols and acids upon exposure to UV irradiation ( 0.3),50 with formation of naphthoquinone methide 71 occurring in the process (Eq. 1.17). 

Lukeman, M. Veale, D. Wan, R Munasinghe, V. R. N. Corrie, J. E. T. Photogeneration of 1,5-naphthoquinone methides via excited-state (formal) intramolecular proton transfer (ESIPT) and photodehydration of 1-naphthol derivatives in aqueous solution. Can. J. Chem. 2004, 82, 240-253. 

Some quinone methides with two MeS groups or one MeS and one Me2N group as donors (47b, 48 to 50) show quite low barriers (49). In the naphthoquinone methides a ground state destabilizing peri effect must be at work, but... 

The products arising from the reaction of the naphthoquinone methide (283) with cis-and rrans-stilbene are different, suggesting that the pericyclic reaction occurs with syn addition (Scheme 75) (73JCS(P1)120). 

Irradiation of 3-hydroxy-2-naphthalenemethanol and 2-hydroxy-l-naphthalene-methanol results in efficient dehydration and the formation of isomeric naphthoquinone methides, 2,3-naphthoquinone-3-methide and 1,2-naphthoquinone-1-methide,... 

Y. Kubo, M. Kuwana, K. Yoshida, Y. Tomotake, T, Matsuzaki, and S. Maeda, Naphthoquinone methide type near-I.R. dye The properties and structure of4-(2-acetylamino-4 -diethylaminophe-nylimino)-l,4-dihydronaphthylidene-malononitrile, J. Chem. Soc., Chem. Commun., 1989 35-37. 

Y. Kubo, K. Yoshida, M. Adachi, S. Nakamura, and S. Maeda, Experimental and theoretical study of near-infrared absorbing naphthoquinone methide dyes with a nonplanar geometry, J. Am. Chem. Soc. 113, 2868-2873 (1991). 

In a related reaction, the photohydrolysis of trifluoromethylnaphthols, the calculated charge distribution in the excited singlet state was found to correlate remarkably well with the excited-state heterolysis rate constants of eight isomeric compounds.328,329 The most reactive of these were the 1,8-, 1,5- and 2,3-substituted derivatives. The primary photoproduct formed from 3-trifluoromethyl-2-naphthol (7, Scheme 4.3), a naphthoquinone methide, was observed by flash photolysis. Depending on the solvent polarity and on the leaving group, homolytic cleavage may, however, compete and reactions that proceed via the triplet state do not necessarily follow the same pattern.330... 

The photoreduction of the naphthoquinone methide (19) has been investigated,35 in connection with Barton s use of photocyclization of derivatives of (19) in tetracycline synthesis.3 Hydrogen abstraction by the triplet of (19) from... 

The conversion of the (Z)-phenylhydrazone of 5-amino-3-benzoyl-l,2,4-oxadiazole into the relevant 1,2,3-triazole in the presence of several haloacetic acids and the kinetics of the rearrangement of (Z)-arylhydrazones of 5-amino-3-benzoyl-l,2,4-oxadiazole to (2-aryl-5-phenyl-2//-l,2,3-triazol-4-yl)ureas have been reported. Treatment of benzannulated enediynyl alcohols with trifluoroacetic acid promoted a cascade sequence of cyclization reactions leading to 1,4-naphthoquinone methides (Scheme 37)7 ... 

Keywords Bioorthogonal reaction Photo-triggered reaction Photoclick Tetrazole Nitrile imine Azirine Cyclopropenone o-Naphthoquinone methide o-Quinodimethanes Hetero Diels-Alder reaction... 

In 2011, Popik and co-workers reported photochemical dehydration of 3-hydroxy-2-naphthalenemethanol (o-naphthoquinone precursor, NQMP, 79) derivatives to o-naphthoquinone methides (oNQMs, 80) [78, 79]. The in situ generated reactive intermediate oNQM underwent facile cycloaddition with vinyl ethers (81) to form photostable benzochromans (82) (Scheme 12). NQMP (79) has two major absorption bands at 275 nm (log s = 4.06) and 324 nm (log s — 3.70) thus it can be photoactivated with either low pressure mercury lamp (254 nm) or fluorescent tubes (300 and 350 nm). The quantum yield of the photoactivation was very high (< 300 = 0.17 0.02 for 79). The in situ generated oNQMs was quenched mostly by... 

In the presence of FeCl3, l-siloxymethyl-l,4-epaxy-l,4-dihydronaphthaIe nes were converted into ortfot-naphthoquinone methides. The in situ nerated oft/io-naphthoquinone methides reacted with allyl silanes via regio- and stere-oseleaive annulations to afford dihydronaphthopyran derivatives (13AGE1515). 

The reaction between o-naphthoquinone methides and thiols has been employed for reversible photochemically-directed surface derivatisation and patterning, through the production of thioether links between the... 

Stable o- and p-naphthoquinone methides leading to (316) have been obtained by a two-stage process, starting with 6-methoxy-l,3,8-tri-hydroxynaphthalene, and studies on the stability conferred on ylides by the phenylimino-group (PhN=) have led to the synthesis shown in Scheme 41 for the formation, in high yield, of the ylide (317) from 2-anilino-3-methylthio-1,4-naphthoquinone (318). 

---