Stereoselective migration of sterically hindered organoboranes in cyclic and acyclic systems. A stereoselective allylic C-H activation reaction

The thermal migration of cyclic and acyclic organoboranes were studied. In most cases, a stereoselective 1,2-dyotropic migration was observed, allowing the stereocontrol of three contiguous chiral centers. Scope and limitations of this thermal migration are presented.     

2-碘-N-甲基苯磺酰胺的合成新方法和分子结构

选用新方法合成了2-碘—N-甲基苯磺酰胺，通过^1H NMR,^13C NMR,^13C DEPT NMR(Distortionless Enhancement by Polarization Transfer NMR)和MS确证的其结构。     

亚直不可约DQrC-环

在文[1]中我们引进了DQ_rC-环,本文给出了忠实的与不忠实的DQ_rC-环为亚直不可约环的充分必要条件.由于DQ_rC-环是比DQC-环更广泛的环类,所以本文推广了W.Burgess等人在DQC-环方面相应的工作.     

Essential domains and two conjectures in dimension theory

This note investigates two long-standing conjectures on the Krull dimension of integer-valued polynomial rings and of polynomial rings in the context of (locally) essential domains.

     

Dubrovin赋值斜群环

本文中对一个斜群环为Dubrovin赋值环给出了一系列等价刻画,并且刻画了一个Dubrovin赋值斜群环的所有素理想.     

An Efficient Method for the Synthesis of 3-Cyano-6-hydroxy-2(1H)-pyridinones under Microwave Irradiation and Solvent-free Conditions

Summary. Three component condensation of alkylacetoacetates, primary amines, and alkyl cyanoacetates catalyzed by solid supports under microwave irradiation gave N-alkyl 3-cyano-6-hydroxy-2(1H)-pyridinones with high yields. Upon carrying out the reaction under the same condition on acidic alumina, zeolite HY, silica gel, and montmorillonite K-10, the best yields were achieved by silica gel. Corresponding author. E-mail: balalaie@yahoo.com Received August 28, 2002; accepted September 3, 2002     

An Improved Synthesis of Retinoic Acid from β-Ionone

A convenient and large-scale preparation of retinoic acid 1 from β-ionone in five steps with 38% overall yield is described.The key steps are the epoxidization of 2 with a new methylated agent and the condensation 4 with tetraethyl methylenediphophonate in one-pot procedure to prepare 6.     

Microwave‐improved polymerization of ϵ‐caprolactone initiated by carboxylic acids

The ring‐opening polymerization of ε‐caprolactone (ε‐CL), initiated by carboxylic acids such as benzoic acid and chlorinated acetic acids under microwave irradiation, was investigated; with this method, no metal catalyst was necessary. The product was characterized as poly(ε‐caprolactone) (PCL) by ¹H NMR spectroscopy, Fourier transform infrared spectroscopy, ultraviolet spectroscopy, and gel permeation chromatography. The polymerization was significantly improved under microwave irradiation. The weight‐average molecular weight (M_w) of PCL reached 44,800 g/mol, with a polydispersity index [weight‐average molecular weight/number‐average molecular weight (M_w/M_n)] of 1.6, when a mixture of ε‐CL and benzoic acid (25/1 molar ratio) was irradiated at 680 W for 240 min, whereas PCL with M_w = 12,100 and M_w/M_n = 4.2 was obtained from the same mixture by a conventional heating method at 210 °C for 240 min. A degradation of the resultant PCL was observed during microwave polymerization with chlorinated acetic acids as initiators, and this induced a decrease in M_w of PCL. However, the degradation was hindered by benzoic acid at low concentrations. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 13–21, 2003     

Synthesis and crystal structure of the octahedral cluster complex [Th(DMSO)8Cl][Re6Se7Cl7]

A cluster complex of the composition [Th(DMSO)₈Cl][Re₆Se₇Cl₇] has been obtained by interaction of ThCl₄ solution in DMSO with a water solution of K₃[Re₆Se₇Cl₇] and KCl. The compound crystallizes in the rhombic space group Pbcm with unit cell parameters a = 12.262(2) Å, b = 19.653(6) Å, c = 23.603(6) Å, V = 5688(2) ų, Z = 4, d _calc = 3.282 g/cm³. The structure is built from centrosymmetric cluster anions [Re₆Se₇Cl₇]^3? and complex cations [Th(DMSO)₈Cl]³⁺ possessing mirror-plane symmetry, half of the DMSO ligands being doubly disordered.