title: Light-induced hetero-Diels-Alder cycloaddition: a facile and selective photoclick reaction.
abstract: 2-Napthoquinone-3-methides (oNQMs) generated by efficient photodehydration (Φ=0.2) of 3-(hydroxymethyl)-2-naphthol undergo facile hetero-Diels-Alder addition (k(D-A)∼ 4×10(4) M(-1) s(-1)) to electron-rich polarized olefins in an aqueous solution. The resulting photostable benzo[g]chromans are produced in high to quantitative yield. The unreacted oNQM is rapidly hydrated (k(H2O) ∼145 s(-1)) to regenerate the starting diol. This competition between hydration and cycloaddition makes oNQMs highly selective, since only vinyl ethers and enamines are reactive enough to form the Diels-Alder adduct in an aqueous solution; no cycloaddition was observed with other types of alkenes. To achieve photolabeling or photoligation of two substrates, one is derivatized with a vinyl ether moiety, while 3-(hydroxymethyl)-2-naphthol is attached to the other via an appropriate linker. The light-induced Diels-Alder "click" strategy permits the formation of either a permanent or hydrolytically labile linkage. Rapid kinetics of this photoclick reaction (k=4×10(4) M(-1) s(-1)) is useful for time-resolved applications. The short lifetime (τ ∼7 ms in H(2)O) of the active form of the photoclick reagent prevents its migration from the site of irradiation, thus, allowing for spatial control of the ligation or labeling.
authors.affiliation: Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA.
authors.forename: Selvanathan
authors.initials: S
authors.lastname: Arumugam
authors.forename: Vladimir V
authors.initials: VV
authors.lastname: Popik
mesh_terms: D002839:Chromans / Q000737:chemistry; D057930:Click Chemistry; D007700:Kinetics; D008027:Light; D009285:Naphthoquinones / Q000737:chemistry; D010782:Photolysis
chemical_list: D002839:Chromans; D009285:Naphthoquinones