Tetsuya Takeya

Transition-State Geometry Measurements from 13C Isotope Effects. The Experimental Transition State for the Epoxidation of Alkenes with Oxaziridines

We here suggest and evaluate a methodology for the measurement of specific interatomic distances from a combination of theoretical calculations and experimentally measured (13)C kinetic isotope effects. This process takes advantage of a broad diversity of transition structures available for the epoxidation of 2-methyl-2-butene with oxaziridines. From the isotope effects calculated for these transition structures, a theory-independent relationship between the C-O bond distances of the newly forming bonds and the isotope effects is established. Within the precision of the measurement, this relationship in combination with the experimental isotope effects provides a highly accurate picture of the C-O bonds forming at the transition state. The diversity of transition structures also allows an evaluation of the Schramm process for defining transition-state geometries on the basis of calculations at nonstationary points, and the methodology is found to be reasonably accurate.

The aryl–aryl coupling reaction of 1-naphthol with SnCl4 for 2,2′-binaphthol synthesis and its application to the biomimetic synthesis of binaphthoquinone isolated from Plumbagozeylanica

Abstract A simple method for the direct synthesis of 2,2′-binaphthols was developed, utilizing aryl–aryl coupling reaction via electron donor–acceptor complexes of 1-naphthols with SnCl 4 . Heating of the complex in a sealed tube afforded the corresponding o - o coupling product in excellent yield. This method was utilized for a biomimetic synthesis of the binaphthoquinone, 3,3′-biplumbagin, isolated from Plumbago zeylanica .

SnCl4-mediated oxidative reaction for formation of binaphthoquinone and dinaphthofuran frameworks and its application to natural product synthesis

Abstract A simple method was developed for the direct synthesis of 2,2′-binaphthoquinones and dinaphtho[1,2-b;2′,1′-d]furans, utilizing an oxidative reaction via electron donor–acceptor complexes of 1-naphthols with SnCl4 in the absence or presence of dioxygen. As an application of this method to natural product synthesis, we describe a facile biomimetic synthesis of several binaphthoquinones, 3,3′-bijuglone, 3,3′-biplumbagin and elliptinone.

OXIDATIVE DIMERIZATION OF 4-METHOXYNAPHTHYLAMINES IN THE PRESENCE OF SEMICONDUCTORS

Three types of 4-methoxynaphthylamines 4a-c were oxidized by treatment with metal oxides under molecular oxygen (O 2 ). 4-Methoxy-1-naphthylamine 4a and 4,6-dimethoxy-1-naphthylamine 4b, on treatment with TiO 2 under O 2 , gave mainly 2-amino-1,4-naphthoquinone derivatives 5a and 5b, respectively whereas 4,8-dimethoxy-1-naphthylamine 4c afforded an unique carbazole 6c as the major product.

One-pot synthesis of dibenzofuran-1,4-diones

One-pot synthesis of dibenzofuran-1,4-diones 8 from 4-methoxyphenols (or 4-methoxy-l-naphthols) 4 was achieved by oxidative dimerization over a semiconductor in heated, O 2 -saturated toluene, followed by selective monodemethylation, and oxidative cyclization.

New reagent system containing CrO3 and syntheses of neo-lignans

Oxidations of 1-arylprop-1-enes by the new reagent systems, CrO3–HBF4–MeCN or CrO3–HCIO4–MeCN gave the 4-aryltetraiones (1a) and (1c), and the tetrahydrofuran (3) which are precursor molecules for aryltetrahydronaphthalene and tetrahydrofuran neo-lignans.