BINOL-based azacrown ether catalyzed enantioselective Michael addition: asymmetric synthesis of α-aminophosphonates

Several novel 1,1′-bi-2-naphthyl-appended azacrown ethers with donor side-arms were synthesized and applied for the first time as chiral catalysts in the asymmetric Michael addition of an N-protected aminomethylenephosphonate onto acrylonitriles, resulting in high diastereoselectivity and enantioselectivity. The absolute configuration of the adduct was determined from its experimental and calculated CD spectra.     

A study on the kabachnik‐‐fields reaction of benzaldehyde,cyclohexylamine, and dialkyl phosphites

The Kabachnik–Fields reaction of benzaldehyde, cyclohexylamine, and dimethyl phosphite carried out at 80°C in acetonitrile takes place via an imine (PhCN ^cHex) intermediate, as the monitoring by in situ Fourier transform IR spectroscopy suggested. The corresponding α‐hydroxyphosphonate was also formed in a quantity of 13% that was not converted to α‐aminophosphonate under the conditions applied. The outcome was similar to the Kabachnik–Fields reaction with diethyl phosphite as the P‐component. Molecular modeling and subsequent DFT calculations carried out under solventless conditions supported the experimental results and indicated the formation of a high number of ideally positioned H bonds as the key determinant for the conformation of the starting, intermediate, and product states. The relative energies of the possible intermediates were in accord with the observation that the formation of the α‐hydroxyphosphonate is a “dead‐end” route. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 23:171–178, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20767     

Microwave‐Assisted Functionalization of Phosphinic Acids: Amidations versus Esterifications

Both the reaction enthalpies and enthalpies of activation obtained by high‐level quantum chemical calculations were against the direct amidation of phosphinic acids under traditional thermal conditions. However, the amidations, not expected to proceed on the basis of the endothermicity and the significantly high enthalpies of activation, did take place under microwave (MW) conditions in 30–36% conversions. As a comparison, the direct esterifications of phosphinic acids that are thermoneutral and have higher enthalpies of activation were quite efficient under MW conditions. The outcome of the MW‐assisted amidation is the balance of two effects. The local overheating effect could overcome the barrier meant by the enthalpy of activation, but the endothermicity works against this. Comparison of the results of the syntheses and the energetics calculated for the esterification and amidation of phosphinic acids enabled us to draw more general conclusions on the scope and limitation of the use of MW irradiation in organic syntheses. The traditional amidation of phosphinic acids via the phosphinic chloride intermediate gave the products in much better yields. © 2013 Wiley Periodicals, Inc. Heteroatom Chem 24:91–99, 2013; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21068     

Synthesis of α‐aminophosphinates by the hydrophosphinylation of imines

Numerous substituted α‐aminophosphinates were synthesized by addition of alkyl and phenyl H‐phosphinates to aromatic imines and characterized. Modest diastereoselectivity was observed in the reaction. The size of the substituents exerts a small effect on the diastereoselectivity of P C bond formation. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:235–240, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10133     

On the stability of small blocking sets

A stability theorem says that a nearly extremal object can be obtained from an extremal one by “small changes”. In this paper, we study the relation of sets having few 0-secants and blocking sets.     

Hydrogenation of schiff bases with group 6 metal carbonyls and sodium methoxide as catalyst precursors

Summary Schiff bases are hydrogenated to secondary amines by H₂ in the presence of [M(CO)₆](M=Cr, Mo or W) and NaOMe in methanol solution at 60–160 °C andca. 100 bar H₂ pressure. The reaction is significantly slower in the absence of NaOMe. In a stoichiometric reaction, [HCr(CO)₅]^– hydrogenatesN- benzylidene-aniline at 75 °C toN-benzylaniline forming [Cr₂(CO)₁₀]^2–.     

Determination of Na,K, Rb and Cs Distribution in Human Brain Using Neutron Activation Analysis

This study aims to investigate the distribution of Na, K, Rb and Cs in human brains (5 individuals, 12 brain parts, mean age: 75 years). Distribution of the trace metals between lipid fraction and brain tissue was investigated in solvent extraction experiments. Determinations were carried out by instrumental neutron activation analysis. The present results show a rather non-homogeneous distribution for Na and a relatively uniform distribution for K, Rb and Cs. The mean concentrations found are 7440µgNag^–1 dry weight, 12800µgKg^–1, 14µgRbg^–1 and 50ngCsg^–1. A highly significant positive correlation was found between Rb and Cs. Solvent extraction experiments showed that 19% of Rb and 26% of Cs of the total content is located in lipid fraction.     

Resolution of 1-substituted-3-methyl-3-phospholene 1-oxides by molecular complex formation with TADDOL derivatives

The antipodes of 1-aryl-, 1-alkyl- and 1-alkoxy-3-methyl-3-phospholene 1-oxides 1a–h and 1-phenyl-3-methyl-3-phospholene 1-sulfide 1i were separated in good yields and high enantiomeric excesses (up to >99% ee) by resolution via formation of diastereomeric complexes with either (−)-(4R,5R)-4,5-bis(diphenylhydroxymethyl)-2,2-dimethyldioxolane 2 (TADDOL) or (−)-(2R,3R)-,,′,′-tetraphenyl-1,4-dioxaspiro[4.5]decan-2,3-dimethanol 3. The stereostructure of the supramolecular formations and the absolute configurations of the 3-phospholene oxides 1a, 1e and 1f were elucidated by single crystal X-ray crystallography. CD spectroscopy was also useful in determining the absolute configurations of some phospholene oxides 1b, 1c, 1g and 1h.