10.1016/j.tet.2015.05.029
The study presents a novel and environmentally friendly heterogeneous catalytic process for the synthesis of 2,3-unsubstituted benzo[b]furans, which are significant structural motifs found in natural products and biologically active molecules. The researchers utilized tin-exchanged H-b zeolite (Sn-b) as a catalyst for the intramolecular cyclization of 2-aryloxyacetaldehyde acetals, achieving good to excellent yields of a wide range of functionalized 2,3-unsubstituted benzo[b]furans. The Sn-b zeolite demonstrated excellent shape selectivity, preferentially forming 6-substituted isomers with up to 97% regioselectivity. It could be easily recovered and reused without significant loss of activity. The study's findings offer an efficient and sustainable method for the production of various benzo[b]furan derivatives, addressing the need for an improved catalyst system over traditional acidic reagents like polyphosphoric acid (PPA) and Amberlyst-15, which have limitations in terms of safety, workup procedure, and mechanical strength.
10.1016/j.steroids.2008.06.002
The research focuses on the synthesis of novel 4-azasteroids, a class of steroidal compounds with potential biological activities, through an intramolecular Ugi reaction. The purpose of this study was to develop a new synthetic strategy that could rapidly generate structurally diverse 4-azasteroids, which are of interest due to their potential as drugs for treating benign prostatic hyperplasia and their antifungal and antibacterial properties. The researchers successfully synthesized a range of 4-azasteroids by varying the nature of the components necessary for the multicomponent reaction, using a variety of amines and isocyanides with cholesterol-derived oxoacid as the starting materials. The conclusions drawn from the study suggest that this methodology can be applied to obtain 4-azasteroids targeted for finding new biologically active compounds, with the structural variety of the side chain depending on the selected isonitrile. The research concluded that, except for aniline and tert-butylamine, the reaction worked well with a set of structurally diverse amines, generating a family of novel N-substituted 4-azasteroids with low stereoselectivity.
10.1016/0022-2860(90)85008-7
The research aimed to investigate the influence of steric hindrance and phenol acidity on the thermodynamic data of formation and proton transfer in phenol-retinal Schiff base hydrogen bonds. Utilizing Fourier transform infrared (FTIR) spectroscopy, the study examined the thermodynamic quantities of hydrogen-bond formation and proton transfer processes across these bonds for four trans-retinal Schiff bases containing different amines (methylamine, n-butylamine, t-butylamine, and n-butyl-nonylamine) and their complexes with 3,4-disubstituted and 4-monosubstituted phenols. The results indicated that the thermodynamic values are significantly influenced by the interaction of the hydrogen bonds with their environment, with the equilibrium shifting to the left as the substituent in the retinal residue becomes more bulky. The study concluded that the large proton polarizability of the hydrogen bonds and the highly ordered arrangement of solvent molecules around the complexes lead to negative and relatively large standard enthalpy and entropy values, which in turn affect the position of the equilibrium. The chemicals used in this process included various phenols, amines, and retinal Schiff bases, with all substances handled in a carefully dried glovebox under an argon atmosphere to ensure experimental accuracy.
10.1021/jo011042o
The research aimed to investigate the impact of ortho, meta, and para substituents on the SN2 reaction rates of phenacyl bromides with tert-butylamine. The study found that substitution rates increased systematically with meta or para substituents of increasing electron-withdrawing ability, while reactivities decreased within an ortho-substituted series. The researchers concluded that ortho-substitution results from rotational barrier effects and an Aδσ+ Bδσ+ repulsion, with the major bonding contribution between the reaction and R-substituent centers being only the σ bond. When π bonding is allowed between A and B (meta/para-substitution), delocalization and stabilization of the reacting center occur.
10.1139/V08-183
The research presents a comprehensive study on the syntheses, X-ray structures, and redox behavior of group 14 bis-boraamidinates, specifically focusing on the complexes M[PhB(m-N-t-Bu)2]2 (where M = Ge, Sn) and Li2M[PhB(m-N-t-Bu)2]2 (where M = Sn, Pb). The purpose of the study was to investigate the redox transformations of these complexes and to explore the possibility of accessing cation radicals {M[PhB(m-N-t-Bu)2]2}+ (M = Si, Ge, Sn) through mild oxidation of the corresponding neutral precursors. The researchers used a variety of chemicals in their experiments, including PhBCl2, GeCl4, SnCl4, SnCl2, PbI2, t-BuNH2, SO2Cl2, and LiN(H)-tBu, among others. The conclusions drawn from the research were that the germanium complex was inert towards oxidizing agents, while the tin complex could be oxidized to form a thermally unstable blue radical cation. The study also characterized the structural and fluctional behavior of the synthesized heterotrimetallic complexes, revealing novel polycyclic arrangements and unique bonding modes within these complexes. The findings provide valuable insights into the electronic structures and potential applications of these group 14 complexes, highlighting the differences in their redox properties compared to their isoelectronic group 13 counterparts.
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