Intramolecular Photocyclization of 2‐Acylphenyl Methacrylates: a Convenient Access to 4,5‐Dihydro‐1,4‐epoxy‐2‐benzoxepin‐3(1H)‐ones (= Benzo[c]‐6,8‐dioxabicyclo[3.2.1]octan‐7‐ones

The photochemical reactions of 2‐acylphenyl methacrylates (= 2‐acylphenyl 2‐methylprop‐2‐enoates) 1 were investigated. Irradiation of 2‐acylphenyl methacrylates 1a – d in MeCN gave the tricyclic lactones 2a – d in good yields, together with a small amount of O CO bond cleavage product, the 2‐acylphenols 3a – d (Scheme 2, Table). The formation of the tricyclic lactones 2 probably follows a mechanism involving a 1,7‐diradical through ζ‐H abstraction (1,8‐H transfer) by the excited carbonyl O‐atom (Scheme 3). Irradiation of 2‐acylphenyl tiglate (= 2‐acylphenyl (2E)‐2‐methylbut‐2‐enoate) 1e and 2‐acylphenyl methacrylates 1g – i , substituted by a MeO group (δ‐H) at the 3,5‐positions of the phenyl group, also gave the tricyclic lactones 2e and 2g – i , but in low yields. On the other hand, no H‐abstraction products were observed on irridation of 2‐(ethoxycarbonyl)phenyl methacrylate 1f , of 2‐acylphenyl methacrylate 1j which is substituted by a Me group (γ‐H) at the 3,5‐positions of the phenyl group, and of 1k with an OH group at the 3‐position of the phenyl group.     

Mechanism for the direct synthesis of tryptophan from indole and serine: a useful NMR technique for the detection of a reactive intermediate in the reaction mixture

The reaction mechanism for the biomimetic synthesis of tryptophan from indole and serine in the presence of Ac₂O in AcOH was investigated. Although the time‐course ¹H‐NMR spectra of the reaction of 5‐methoxyindole with N‐acetylserine were measured in the presence of (CD₃CO)₂O in CD₃CO₂D, the reactive intermediate could not be detected. This reaction was conducted without 5‐methoxyindole in order to elucidate the reactive intermediate, but the intermediate could not be isolated from the reaction mixture. Since the intermediate would be expected to have a very short life time, and therefore be very difficult to detect by conventional analytical methods, the structure of the intermediate was elucidated using a 2D‐NMR technique, diffusion‐ordered spectroscopy (DOSY). Two intermediates were detected and confirmed to be 2‐methyl‐4‐methyleneoxazol‐5(4H)‐one and 2‐methyl‐4‐hydroxymethyloxazol‐5(4H)‐one. The present results demonstrated that DOSY is a powerful tool for the detection of unstable intermediates. Copyright © 2010 John Wiley & Sons, Ltd.     

Initial stage of the adsorption of fluorofullerene molecules on Si surface

Spatially resolved images of an individual C₆₀F₁₈ fluorofullerene molecule on Si(100) − 2 × 1 surface have been obtained using scanning tunneling microscopy. Scanning tunneling microscopy results and ab initio calculations show that the fluorofullerene molecules interact with the Si(100) − 2 × 1 surface with F atoms pointing down towards the surface. The adsorption energy of a C₆₀F₁₈ molecule on Si(100) − 2 × 1 surface is ∼12.1 eV, which is much higher than the adsorption energy of the same molecule on Si(111) − 7 × 7 surface (6.65 eV). C₆₀F₁₈ molecules are located in the troughs in-between the dimer rows occupying the four-dimer site on Si(100) − 2 × 1 surface.     

Oxovanadium(v)-catalyzed oxidative biaryl synthesis from organoborate under O2

Oxidative ligand coupling of organoborates was catalyzed by VO(OEt)Cl(2) under oxygen atmosphere, which provides a versatile method for the selective synthesis of symmetrical or unsymmetrical biaryls.