An Efficient Four‐component Synthesis of Spiro[indoline‐pyrazolo[4′,3′:5,6]pyrido[2,3‐d]pyrimidine]triones

A four‐component reaction in the presence of Alum [KAl(SO₄)₂·12H₂O] as an inexpensive and reusable catalyst using the ionic liquid as an effective green reaction media is reported.     

A new class of stereoregular vinylene‐arylene copolymers with double‐decker silsesquioxane in the main chain

A synthesis of a new macromolecular class of vinylene‐arylene copolymers with double‐decker silsesquioxane in the main chain is presented. Two transition‐metal‐catalyzed processes, which is silylative‐coupling copolycondensation (SCC) and ADMET copolymerization of divinyl‐substituted double‐decker silsesquioxanes (DDSQ‐2SiVi) with selected diolefins, are reported to be highly efficient tools for the formation of stereoregular copolymers containing DDSQ‐silylene‐vinylene‐arylene units. The copolymeric products are studied in terms of their structural, thermal, and mechanical properties. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1044–1055     

Intermolecular condensation products formed during the pyrolysis of peptides

Mass Spectrometry (MS) analysis of pyrolysis products of simple peptides has revealed several non-volatile thermal degradation products at masses lower than the precursor peptide. In addition to these products, many other signals were also observed at higher masses than the precursor peptide, and their characterization is the focus of this study. Here we report on the observation of homo and hetero condensation peptide products formed during the pyrolysis of peptides. The observed peptide condensation products are formed between two, three or even four peptides. Tandem MS (MS/MS) analyses of these products showed that C-terminal to N-terminal intermolecular bonding is preferred during pyrolysis when combining two peptides, rather than involving crosslinking between basic and acidic side chain groups like arginine and aspartic acid. These observations are rationalized by steric hindrance effect and known pK_a values of the peptide C- and N-termini and amino acid side groups like aspartic acid and arginine. Pyrolysis of a standard N-acetylated peptide showed no detectable condensation and/or crosslinked products, even in peptides with basic side groups, providing further evidence for the C-terminus to N-terminus intermolecular bonding between peptides under pyrolytic conditions.     

Synthetic studies on C14 cembranoids: synthesis of C4-12 fragment of sarcophytonolides E-G and L and C5-11 fragment of sarcophytonolide L

An efficient stereoselective synthesis of C4-12 fragment of the cembranoids, sarcophytonolides E-G and L and C5-11 fragment of sarcophytonolide L is described. The C4-12 building block is efficiently assembled starting from chiral pool material (R)-carvone employing the Baeyer-Villiger oxidation, modified Knoevenagel condensation and asymmetric dihydroxylation as the key steps. The synthesis of C5-11 fragment is based on orthoester Johnson-Claisen rearrangement as the key step.     

The first total synthesis and structural determination of antibiotics K1115 B1s (alnumycins)

K1115 B₁, isolated from the broth of Streptomyces species, was found to be a mixture of stereoisomers. Authors synthesized all stereoisomers of K1115 B₁ by convergent synthesis coupling a rhamnose derivative, an isobenzofuranone, and a chiral tetraol. Comparison of ¹H NMR spectra and optical rotations made it clear that the absolute structures of K1115 B_1α (the major isomer) and K1115 B_1β (the minor isomer) were (1R, 17S)- and (1R, 17R)-configurations, respectively. The optical rotations of the stereoisomers revealed that alnumycin, reported as the identical structure with K1115 B₁, might be another mixture of stereoisomers.     

醋酸溶液中2,3-二芳基-喹喔啉的简便合成

1,2-二芳基乙二酮与1,2-苯二胺在室温醋酸溶液中反应数分钟,生成2,3-二芳基一喹喔啉.反应时间短(1～10min),产率高(90%～97%),反应条件温和,操作简便.     

A new chemical access for 3′-acetyl-4′-hydroxychalcones using borontrifluoride-etherate via a regioselective Claisen-Schmidt condensation and its application in the synthesis of chalcone hybrids

A new chemical access has been developed for the synthesis of 3′-acetyl-4′-hydroxychalcones from 1-(5-acetyl-2-hydroxy-phenyl)-ethanone and various substituted benzaldehydes via a regioselective Claisen-Schmidt condensation using borontrifluoride-etherate (BF₃·OEt₂) at room temperature, in good to excellent yields within 12-24 h. Application of this methodology has also been demonstrated in the synthesis of chalcone hybrids.     

A mathematical discussion of Pons Viver's implementation of Löwdin's spin projection operator

Recently, the molecular electronic structure theories for efficiently treating static (or strong) correlation in a black-box manner have attracted much attention. In these theories, a spin projection operator is used to recover the spin symmetry of a broken-symmetry Slater determinant. Very recently, Pons Viver proposed the practical and exact implementation of Löwdin's spin projection operator (Int. J. Quantum Chem. 2019, 119, e25770). In the present study, we attempt to supply mathematical proofs to Pons Viver's proposals and show a condition for establishing Pons Viver's implementation. Moreover, we explicitly derive the (spin projected) extended Hartree-Fock (EHF) equations on the basis of the model of common orbitals (ie, closed-shell orbitals used in the restricted open-shell Hartree-Fock (ROHF) method), which was combined by Pons Viver with the EHF method.