BINAPHANE-catalyzed asymmetric synthesis of trans-β-lactams from disubstituted ketenes and N-tosyl arylimines

The development of a BINAPHANE-catalyzed formal [2 + 2]-cycloaddition of disubstituted ketenes and inexpensive N-tosyl arylimines that provides access to a variety of highly substituted β-lactams (16 examples) is described. The BINAPHANE catalytic system displays moderate to excellent enantioselectivity (up to 98% ee) and high diastereoselectivity in most cases, favoring formation of the trans-diastereomer (13 examples with dr ≥ 90:10).     

Pyridine-substituted hydroxythiophenes. II. Alkylation of o-(2-, 3- and 4-pyridyl)-3-hydroxythiophenes: Regiospecific formation of o-pyridyl-3-alkoxythiophenes

The alkylation of o-(2-, 3- and 4-pyridyl)-3-hydroxythiophenes has been investigated. In the case of 4-(2-, 3- and 4-pyridyl)-3-hydroxythiophene systems, the soft alkylating reagent, methyl iodide, using sodium hydride as the base and dimethylimidazolidinone as the solvent, gave rise to a mixture of O-alkylated and O,C-dialkylated products in the proportions of 4.6–6.5 to 1. However, in the case of 2-(2-, 3- and 4-pyridyl)-3-hydroxythiophene systems, the same reaction conditions brought about exclusively O-alkylated compounds in yields of 45–53%. In both cases, the hard alkylating reagent, methyl p-toluenesulfonate, with the same base and solvent, only give O-alkylated compounds in yields of 51–77%. These latter conditions resulted in a good preparative route for the regiospecific formation of o-pyridyl-3-alkoxythiophenes by using ethyl 2-bromopro-pionate as well as methyl p-toluenesulfonate as alkylating reagents. The hydrolysis of the esters, derived from alkylation with ethyl 2-bromopropionate, has also been investigated.     

Synthesis of various 5-(3-substituted phenyl)-2′-deoxyuridines

A series pf 5-aryl-2′-deoxyuridines has been prepared and evaluated as antiviral agents. The following substituents have been used in position 3 of the phenyl ring: chloro, iodo, amino, azido, methylthio, and vinyl. None of the new compounds showed any significant activity when tested against human immunodeficiency virus 1 (HI V-I), herpes simplex virus 1 (HSV-I), or human cytomegalovirus (HCMV).     

The Method of R-Functions in the Solution of Elastic Problems on the Basis of Reissner's Mixed Variational Principle

A method is presented for solving boundary-value elastic problems on the basis of the variational–structural method of R-functions and Reissner's mixed variational principle. A mathematical formulation is given to problems on the deformation of elastic bodies under mixed boundary conditions and bodies interacting with smooth rigid dies. Solutions satisfying all the boundary conditions are proposed. For undetermined components of these solutions, the resolving equations are derived and their properties are studied. A posteriori estimation of numerical solutions is made. As examples, solutions are found to a problem on the stress–strain state of a short cylinder and to a contact problem on a cylinder interacting with a smooth die. A numerical method of solving such problems is analyzed for convergence, and the accuracy of the solutions is estimated.     

Excess sodium ions improve Z selectivity in Horner-Wadsworth-Emmons olefinations with the Ando phosphonate

New, improved conditions for Z selective Horner-Wadsworth-Emmons olefinations with Ando's bis(o-methylphenyl)phosphonates are reported. A combination of NaH and NaI affords Z olefins in up to >99:1 selectivity and good yields.     

Universal gates with wires in a row

Journal of Algebraic Combinatorics - Koornwinder polynomials are q-orthogonal polynomials equipped with extra five parameters and the $$B C_n$$ -type Weyl group symmetry, which were introduced by...     

Semiclassical Pseudodifferential Calculus and the Reconstruction of a Magnetic Field

We give a procedure for reconstructing a magnetic field and electric potential from boundary measurements given by the Dirichlet to Neumann map for the magnetic Schrödinger operator in R ⁿ , n ≥ 3. The magnetic potential is assumed to be continuous with L ^∞ divergence and zero boundary values. The method is based on semiclassical pseudodifferential calculus and the construction of complex geometrical optics solutions in weighted Sobolev spaces.     

On the selectivity in the bromination of selenophene-2-carbonyl derivatives in the presence of aluminum trichloride

Bromination reactions of 2-selenophenecarbaldehyde and 2-acetylselenophene in the presence of aluminum trichloride have been investigated and the reactivity and positional selectivity compared with those of the analogous thiophene derivatives.     

Application of principal component analysis to 13C NMR shifts of chalcones and their thiophene and furan analogues: A useful tool for the shift assignment and for the study of substituent effects

¹³C NMR shifts of 54 chalcones and their thiophene and furan analogues are analyzed by principal component analysis. Thus, a mathematical model is derived for the variation of the carbon shifts in each of seven classes. Two component models are found to be adequate by cross-validation. The first component corresponds to ordinary σ_para values, while the second one differentiates benzenes, thiophenes and furans. This type of data analysis is a useful tool for checking the consistencies of spectral parameters. The model parameters, which describe systematic variations within each class, are also used for the study of substituent effects and discussed in relation to substituent constants in linear free energy relationships.     

Synthesis of various 5-substituted 2′-deoxy-3′-5′-di-O-acetyluridines

The Pd(0)-catalyzed coupling reaction of β-5-iodo-2′-deoxy-3′,5′-di-O-acetyluridine with various heteroaryltrimethylstannyl compounds gave the corresponding β-5-heteroaryl-2′-deoxy-3′,5′-di-O-acetyluridines in moderate yields. This direct coupling approach for nucleosides represented an interesting alternative to the 5-heteroaryl functionalization of pyrimidines followed by the Hilbert-Johnson glycosylation reaction which often yields mixtures of the α and β anomers.