Competing photodehydration and excited-state intramolecular proton transfer (ESIPT) in adamantyl derivatives of 2-phenylphenols

Abstract

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.

In vitro investigation of the antimicrobial activity of a series of lipophilic phenols and naphthols

“…(10) was prepared in a Grignard reaction from adamantan-2-one and 2-bromo-2'-methoxybiphenyl in 76 % yield according to the published procedure. 20 Characterization of product 10 compares well with literature (mp = 114-115°C). 20 2-(2-Hydroxyadamantan-2-yl)-2'-hydroxybiphenyl (11) was prepared from 10 by treatment with sodium thiolate in 60 % yield according to the published procedure.…”

“…20 Characterization of product 10 compares well with literature (mp = 114-115°C). 20 2-(2-Hydroxyadamantan-2-yl)-2'-hydroxybiphenyl (11) was prepared from 10 by treatment with sodium thiolate in 60 % yield according to the published procedure. 20 Characterization of product 11 compares well with literature (mp = 194-196°C).…”

“…All compounds were prepared according to previously published procedures. [19][20][21][22][23] Chiral compounds 7-9 were synthesized as racemic mixtures.…”

“…20 2-(2-Hydroxyadamantan-2-yl)-2'-hydroxybiphenyl (11) was prepared from 10 by treatment with sodium thiolate in 60 % yield according to the published procedure. 20 Characterization of product 11 compares well with literature (mp = 194-196°C). (12) was prepared from 3-(2-hydroxyadamantan-2-yl)-2'-methoxybiphenyl by treatment with BBr 3 in 69 % yield according to the published procedure.…”

“…18 We became interested in the photochemical generation of QMs with sterically congested lipophylic substituents 19,20 and their antiproliferative activities. [21][22][23][24] A series of simple phenols, 19 biphenyls, [20][21][22] naphthols, 23 and anthrols 24 were synthesized and their antiproliferative activities were investigated. Since compounds that generate QMs are known b-lactamase inhibitors, 18 we were also prompted to investigate their antimicrobic activities.…”