Palladium-catalyzed intermolecular alpha-arylation of zinc amide enolates under mild conditions

The intermolecular alpha-arylation and vinylation of amides by palladium-catalyzed coupling of aryl bromides and vinyl bromides with zinc enolates of amides is reported. Reactions of three different types of zinc enolates have been developed. The reactions of aryl halides occur in high yields with isolated Reformatsky reagents generated from alpha-bromo amides, with Reformatsky reagents generated in situ from alpha-bromo amides, and with zinc enolates generated by quenching lithium enolates of amides with zinc chloride. This use of zinc enolates, instead of alkali metal enolates, greatly expands the scope of amide arylation. The reactions occur at room temperature or 70 degrees C with bromoarenes containing cyano, nitro, ester, keto, fluoro, hydroxyl, or amino functionality and with bromopyridines. Moreover, the reaction has been developed with morpholine amides, the products of which are precursors to ketones and aldehydes. The arylation of zinc enolates of amides was conducted with catalysts bearing the hindered pentaphenylferrocenyl di-tert-butylphosphine (Q-phos) or the highly reactive, dimeric, Pd(I) complex [[P(t-Bu)3]PdBr]2.     

ESR study of linear aliphatic oligoesters under γ-irradiation. I. Paramagnetic species produced in the material by irradiation at 77°K

Paramagnetic species produced in a series of linear aliphatic oligoesters $ [\bond;{\rm O}\bond;({\rm CH}_{\rm 2} {\rm )}_m\bond;{\rm O}\bond;{\rm CO}\bond;({\rm CH}_{\rm 2} {\rm )}_n\bond;{\rm CO\rlap{--} ]}_P $ by γ-irradiation at 77°K was investigated by an ESR method. A predominant doublet observed immediately after γ-irradiation, which has hyperfine splitting of 20–23 gauss, is attributed to a radical anion III. Slight decay of this radical anion is observed by illuminating the sample with visible light at 77°K. A small amount of the radical anion is converted to double triplet, which is assigned to ? (ES)? CH? CH₂? (where ES denotes the ester group), from the result of heat treatment. The conformational angles for the two β-protons in the (6,2) oligoester are determined to be θ₁ = θ₂ = 30°.     

LASER PHOTOLYSIS STUDIES OF SUPEROXIDE ADDUCTS OF COBALT(II) AND ZINC(II) PORPHYRINS IN DIMETHYLFORMAMIDE

Abstract— Photochemistry of superoxide adducts of cobalt(II) and zinc(II) porphyrins has been studied by laser photolysis. It was found that the former in dimethlformamide photodissociates the superoxide anion radical, O₂^-, with the quantum yield of 0.5 ± 0.05 at the excitation wavelenths 355 and 532 nm, and the latter gives flurescence and the triple state without giving rise to the photodissociation of O₂^-     

Effects of quantitative disorder on the electronic structure of tetrahedrally-bonded amorphous semiconductors

We have studied the effects of quantitative disorder on the valence band in the electronic density of states (DOS) of tetrahedrally-bonded amorphous semiconductors on the basis of a simple Weaire-Thorpe model. The coherent potential approximation is applied to the random variation of the transfer integrals V₁ and V₂ of the model. Our numerical results indicate that it is not always necessary to assume the existence of five-membered rings in order to explain the characteristic features of the DOS.     

Cascade‐ and Orthoamide‐Type Overman Rearrangements of Allylic Vicinal Diols

This article describes the details of two new types of Overman rearrangement from allylic vicinal diols. Starting from identical diols, both bis(imidate)s and cyclic orthoamides were selectively synthesized by simply changing the reaction conditions. Whilst exposure of the bis(imidate)s to thermal conditions initiated the double Overman rearrangement to introduce two identical nitrogen groups in a single operation (the cascade‐type Overman rearrangement), the reaction of cyclic orthoamides resulted in a single rearrangement (the orthoamide‐type Overman rearrangement). The newly generated allylic alcohols from the orthoamide‐type reaction can potentially undergo a variety of further transformations. For instance, we demonstrated an Overman/Claisen sequence in one pot. The most conspicuous feature of this method is that it offers precise control over the number of Overman rearrangements from the same allylic vicinal diols. This method also excludes the tedious protecting‐group manipulations of the homoallylic alcohols, which are necessary in conventional Overman rearrangements. All of the performed rearrangements proceeded in a completely diastereoselective fashion through a chair‐like transition state.     

Synthesis and structure of triply bridged purinophanes

The title compounds were synthesized as a model for studying the relationship between the hypochromism and the stacking mode of two purine rings. By comparing 1 with other purinophanes it was concluded that the fully overlapped orientation of two purine rings gives the largest hypochromicity.     

Frequency dependence of the spin-lattice relaxation time in solid H2 with very low concentration of ortho-molecules

By extending the previous theory of Hama et al. for the spectral density in the system of randomly distributed spins with R^–n-interactions, the frequency dependence of the spin-lattice relaxation time of o-H₂ in solid H₂ at very low concentration is studied, with results in excellent agreement with measurements. In the present extension the effects of the anisotropy and rotational Zeeman energies have been taken into account by the use of the measured constants relevant to both energies.