Hydroxymethylphenols strategically substituted with the 2-hydroxy-2-adamantyl moiety, AdPh 8-10, were synthesized, and their photochemical reactivity was investigated. On excitation to the singlet excited state, AdPh 8 undergoes intramolecular proton transfer coupled with a loss of H(2)O giving quinone methide 8QM. The presence of 8QM has been detected by laser flash photolysis (CH(3)CN-H(2)O 1:1, tau = 0.55 s) and UV-vis spectroscopy. Singlet excited states of AdPh 9 and 10 in the presence of H(2)O dehydrate giving 9QM and 10QM. Photochemically formed QMs are trapped by nucleophiles giving the addition products (e.g., Phi for methanolysis of 8 is 0.55). In addition, the zwitterionic 9QM undergoes an unexpected rearrangement involving transformation of the 2-phenyl-2-adamantyl cation into the 4-phenyl-2-adamantyl cation (Phi approximately 0.03). An analogous rearrangement was observed with methoxy derivatives 9a and 10a. Zwitterionic 9QM was characterized by LFP in 2,2,2-trifluoroethanol (tau = 1 mus). In TFE, in the ground state, AdPh 10 is in equilibrium with 10QM, which allowed for recording the (1)H and (13)C NMR spectra of the QM. Introduction of the adamantyl substituent into the o-hydroxymethylphenol moiety increased the quantum yield of the associated QM formation by up to 3-fold and significantly prolonged their lifetimes. Furthermore, adamantyl substituent made the study of the alkyl-substituted quinone methides easier by LFP by prolonging their lifetimes and increasing the quantum yields of formation.

2-Phenylphenol derivatives strategically substituted with a hydroxyadamantyl substituent were synthesized and their photochemical reactivity was investigated. Derivatives 9 and 10 undergo competitive excited-state intramolecular proton transfer (ESIPT) from the phenol to the carbon atom of the adjacent phenyl ring and formal ESPT from the phenol to the hydroxyl group coupled with dehydration. These two processes (both via S1) give rise to two classes of quinone methides (QMs) that revert to starting material or react with nucleophiles, respectively. ESIPT to carbon atoms was studied by performing photolyses in the presence of D2O, whereupon deuterium incorporation to the adjacent phenyl ring was observed ([Formula: see text] = 0.1–0.2). The competing formal ESPT and dehydration takes place with quantum yields that are an order of magnitude lower and was studied by isolation of photomethanolysis products. Derivative 8 did not undergo ESIPT to carbon atom. Owing to the presence of an intramolecular H bond, an efficient ESIPT from the phenol to the hydroxyl group coupled with dehydration gives a QM that efficiently undergoes electrocyclization (overall [Formula: see text] = 0.33), to give chroman 16. In addition, spiro[adamantane-2,9′-(4′-hydroxy)fluorene] (12) undergoes ESIPT, unlike the previously reported unreactive parent 2-hydroxyfluorene. The reactive singlet excited states of the prepared biphenyl and fluorene molecules were characterized by fluorescence spectroscopy, whereas laser flash photolysis (LFP) was performed to characterize the longer lived QM intermediates.

Five groups of phenols/naphthols (42 compounds in total) were synthesized and screened against Gram-positive Staphylococcus aureus and Bacillus subtilis, Gram-negative Escherichia coli and Klebsiella pneumoniae, and the fungus Candida albicans. Whereas compounds were found inactive against Gram-negative bacteria, potent activities against Gram-positive bacteria were observed. The activities correlate with the ability of molecules to form quinone methides, suggesting potential new modes of action.