Synthesis of cetyltrimethylammonium tribromide (CTMATB) and its application in the selective oxidation of sulfides to sulfoxides

The bright yellow crystalline cetyltrimethylammonium tribromide (CTMATB) reagent has been synthesized from the reaction of CTMAB and KBr with H₂MoO₄·H₂O, H₂O₂ and H₂SO₄ in the molar ratio 1:2:0.01:4:0.93. CTMATB selectively oxidizes a variety of dialkyl and alkyl aryl sulfides to the corresponding sulfoxides in high yields under mild conditions.     

Morita equivalence of dual operator algebras

We consider notions of Morita equivalence appropriate to weak* closed algebras of Hilbert space operators. We obtain new variants, appropriate to the dual algebra setting, of the basic theory of strong Morita equivalence, and new nonselfadjoint analogues of aspects of Rieffel’s W^∗-algebraic Morita equivalence.     

Rigged modules I: Modules over dual operator algebras and the Picard group

In a previous paper we generalized the theory of $W^{?}$-modules to the setting of modules over nonselfadjoint dual operator algebras, obtaining the class of weak^?-rigged modules. At that time we promised a forthcoming paper devoted to other aspects of the theory. We fulfill this promise in the present work and its sequel “Rigged modules II”, giving many new results about weak^?-rigged modules and their tensor products. We also discuss the Picard group of weak* closed subalgebras of a commutative algebra. For example, we compute the weak Picard group of $H^{\infty }(\mathbb{D})$, and prove that for a weak* closed function algebra A, the weak Picard group is a semidirect product of the automorphism group of A, and the subgroup consisting of symmetric equivalence bimodules.     

11-Step enantioselective synthesis of (-)-lomaiviticin aglycon

Lomaiviticins A and B are complex antitumor antibiotics that were isolated from a strain of Micromonospora. A confluence of several unusual structural features renders the lomaiviticins exceedingly challenging targets for chemical synthesis. We report an 11-step, enantioselective synthetic route to lomaiviticin aglycon. Our route proceeds by late-stage, stereoselective dimerization of two equivalent monomeric intermediates, a transformation that may share parallels with the natural products' biosyntheses. The route we describe is scalable and convergent, and it lays the foundation for determination of the mode of action of these natural products.     

Bioactive diterpenoid containing a reversible "spring-loaded" (E,Z)-dieneone Michael acceptor

Three new briarane diterpenoids, briareolate esters L-N (1-3), have been isolated from a gorgonian Briareum asbestinum. Briareolate esters L (1) and M (2) are the first natural products possessing a 10-membered macrocyclic ring with a (E,Z)-dieneone and exhibit growth inhibition activity against both human embryonic stem cells (BG02) and a pancreatic cancer cell line (BxPC-3). Briareolate ester L (1) was found to contain a "spring-loaded" (E,Z)-dieneone Michael acceptor group that can form a reversible covalent bond to model sulfur-based nucleophiles.     

Regioselective Alkylative Carboxylation of Allenamides with Carbon Dioxide and Dialkylzinc Reagents Catalyzed by an N‐Heterocyclic Carbene–Copper Complex

The alkylative carboxylation of allenamide catalyzed by an N‐heterocyclic carbene (NHC)–copper(I) complex [(IPr)CuCl] with CO₂ and dialkylzinc reagents was investigated. The reaction of allenamides with dialkylzinc reagents (1.5 equiv) and CO₂ (1 atm.) proceeded smoothly in the presence of a catalytic quantity of [(IPr)CuCl] to afford (Z)‐α,β‐dehydro‐β‐amino acid esters in good yields. The reaction is regioselective, with the alkyl group introduced onto the less hindered γ‐carbon, and the carboxyl group introduced onto the β‐carbon atom of the allenamides. The first step of the reaction was alkylative zincation of the allenamides to give an alkenylzinc intermediate followed by nucleophilic addition to CO₂. A variety of cyclic and acyclic allenamides were found to be applicable to this transformation. Dialkylzinc reagents bearing β‐hydrogen atoms, such as Et₂Zn or Bu₂Zn, also gave the corresponding alkylative carboxylation products without β‐hydride elimination. The present methodology provides an easy route to alkyl‐substituted α,β‐dehydro‐β‐amino acid ester derivatives under mild reaction conditions with high regio‐ and stereoselectivtiy.     

A Morita theorem for dual operator algebras

We prove that two dual operator algebras are weak^∗ Morita equivalent in the sense of [D.P. Blecher, U. Kashyap, Morita equivalence of dual operator algebras, J. Pure Appl. Algebra 212 (2008) 2401-2412] if and only if they have equivalent categories of dual operator modules via completely contractive functors which are also weak^∗-continuous on appropriate morphism spaces. Moreover, in a fashion similar to the operator algebra case, we characterize such functors as the module normal Haagerup tensor product with an appropriate weak^∗ Morita equivalence bimodule. We also develop the theory of the W^∗-dilation, which connects the non-selfadjoint dual operator algebra with the W^∗-algebraic framework. In the case of weak^∗ Morita equivalence, this W^∗-dilation is a W^∗-module over a von Neumann algebra generated by the non-selfadjoint dual operator algebra. The theory of the W^∗-dilation is a key part of the proof of our main theorem.     

Variation of focus action with electrode length for an innerelectrode of negative polarity

A 2.3 kJ plasma focus (PF) device was used to investigate the variation of focus action with electrode length using argon, air, and nitrogen as filling gases. It was observed that for an inner electrode (IE) of negative polarity, the focus action improved tremendously as the electrode lengths were reduced from 80 to 40 mm. The high voltage (HV) pulse width also decreased with the decrease in electrode lengths. Third, the best focus peak of the HV pulse was shifted toward higher focus pressures, and the range for good focus action was broader. There is a tendency toward improvement of focus action toward significantly shorter IE lengths (about 40 mm) for negative polarity as compared to positive polarity, where the optimum IE length is 150 mm. This suggests that plasma contamination due to ablated IE material is minimized with shorter electrode length for negative IE. This could provide part of the solution to the polarity riddle of PF devices in relation to neutron production     

An efficient RuCl3·H2O/I2 catalytic system: A facile access to 3-aroylimidazo[1,2-a]pyridines from 2-aminopyridines and chalcones

A simple and efficient protocol has been demonstrated for the preparation of densely functionalized 3-aroylimidazo[1,2-a]pyridines from 2-aminopyridines and chalcones using RuCl₃·H₂O/I₂ catalytic system. The advantages, such as low catalyst loading, broad substrate scope with respect to substitutions on aminopyridines as well as chalcones, stability of heterocycles such as thiophene under the reaction conditions, operationally simple procedure and higher yields makes this approach remarkable for synthetic applications.     

A computational approach to understanding the mechanism of aromatic bromination using quaternary ammonium tribromides

Quaternary ammonium tribromides (QATBs) have garnered interest for nearly a century now. Various types of tribromides have been synthesized over the years and their diverse applications have been extensively reported. However, despite the fact that these reagents are touted as safer alternatives to the very poisonous bromine, there is insufficient information on the structure of Br₃^? in QATB systems and there is still no clear explanation for how the tribromide ion (Br₃^?) participates in bromination reactions. This paper reports a through structural assessment of Br₃^?, followed by an attempt was made to fully understand the mechanistic behaviour of tribromide during bromination of aromatic compounds.