Showing papers on "Boron tribromide published in 1999"

Synthesis and electrochemistry of platinum complexes of hydroquinon-2-ylmethyl- and p-benzoquinon-2-ylmethyl-diphenylphosphine

Abstract: Platinum(II) complexes of new (hydroquinon-2-ylmethyl)diphenylphosphine (PPh2thqH2) and diphenyl(quinon-2-ylmethyl)phosphine (PPh2tq) ligands have been studied. Reaction of (2,5-dimethoxybenzyl)diphenylphosphine (PPh2dmb) with [PtCl2(PhCN)2] afforded [PtCl2(PPh2dmb)2] 1a. Metathesis reactions gave the bromo (1b) and iodo (1c) congeners. Deprotection of the hydroquinone groups in 1a using boron tribromide followed by treatment with base produced the O,P-chelated hydroquinonate phosphine complex, cis-[Pt(O,P-PPh2thqH)2] 2. Reaction of 2 with hydrobromic acid afforded cis-[PtBr2(PPh2thqH)2] 3 which can be oxidised to give the quinone phosphine complex cis-[PtBr2(PPh2tq)2] 4. Unlike previously reported quinone phosphine complexes, 4 is robust and stable to hydrolysis; its reduction with excess of zinc and dilute hydrobromic acid produced cis-[Pt(O,P-PPh2thqH)2(ZnBr2)] 5. Crystal structure analyses of 2·2dmf, 4·0.5dcm and 5·2dmf were performed. The electrochemistries of 1b, 3, and 4 have been characterised by cyclic voltammetry and controlled potential electrolyses. Cyclic voltammograms of 4 in the presence of dilute hydrobromic acid exhibit a four-electron cathodic process, attributed to reduction to 3; those of 3 show an anodic process attributed to oxidation to 4. The electrochemistry of 4 under aprotic conditions is extraordinary. Although there are two well separated, pendant quinone substituents only a single one-electron reduction process is observed. The reduction affords a radical species (6˙–) which has been characterised by cyclic voltammetry, and by EPR and UV/Vis/NIR spectroscopy. It is argued from the available data that 6˙– is a novel platinum(IV) complex with bound hydroquinonate and semiquinonate (sq) groups, namely [PtBr2(O,P-PPh2thq)(O,P-PPh2tsq˙)]–, and a possible mechanism for its remarkable formation is discussed.

Reactivity of Sodium Hexaethyl-2,4-dicarba- nido -hexaborate(1 - )

Abstract: Sodium hexaethyl-2,4-dicarba- nido -hexaborate(1 - ) ( 6 ), available from hexaethyl-2,4-dicarba- nido -hexaborane(8) ( 4 ) by deprotonation, reacts with deuterated methanol, CD 3 OD, to give back 4 without H/D exchange of the B-H-B hydrogen atom. The reaction of 6 with diethylboron chloride, Et 2 BCl, affords hexaethyl-2,4-dicarba- closo -hexaborane(6) ( 7 ), the first example of a peralkylated carborane of this type. In contrast, the reaction of 6 with boron tribromide, BBr 3 , leads mainly to 2,3,4,5,6,7-hexaethyl-2,4-dicarba- closo -heptaborane(7) ( 8 ), together with the corresponding 1-bromo derivative ( 9 ) and the closo -carborane 7 as side products. The reaction of two equivalents of 6 with FeCl 2 gives the air-stable sandwich complex bis[hexaethyl-2,4-dicarba- nido -hexaborate(1 - )]iron 10 which was characterised by X-ray structural analysis. All products were characterised by 1 H, 11 B and 13 C NMR spectroscopy, and 57 Fe Mossbauer spectroscopy was used to study 10 .

Synthesis and Investigations on Nitrido(phthalocyaninato)rhenium Complexes

Abstract: The reactions of nitrido(tetra-tert-butylphthalocyaninato)rhenium (1) with boron tribromide leading to (tBu4Pc)ReNBBr3 (4) and with acetone to give the imido complex (tBu4Pc)Re[NC(CH3)2CH2C(O)CH3]OH (2b) and its μ-oxo dimer 3 are reported. Starting from the corresponding 4,5-di-n-alkylphthalonitriles and ammonium perrhenate four soluble nitrido(octa-n-alkylphthalocyaninato)rhenium complexes 5–8 were synthesized. Nitrido(octa-n-pentylphthalocyaninato)rhenium (6) was treated with boron tribromide to afford [(C5H11)8Pc]ReNBBr3 (9).

The Total Synthesis of Salvianolic Acid F.

Abstract: An expeditious synthesis of salvianolic acid F 2 is described in 10% overall yield. Tetramethyl salvianolic acid F 3 was obtained in six steps in 39% overall yield and was converted into the target molecule using boron tribromide in 26% yield.

Chlorine-based polymer

Abstract: PROBLEM TO BE SOLVED: To obtain a chlorine-based polymer capable of suppressing the production of chlorides such as dioxin even when subjected to an incinerating treatment, excellent in environmental pollution resistance and useful for a container, a decorative sheet, a wrapping film, etc., by adding a reducing agent to a chlorine-based substrate resin. SOLUTION: This polymer is obtained by adding preferably 0.01-60 wt.% of a reducing agent such as phosphorous acids, hypophosphorous acids, metal hydrides (e.g. an alkylaluminum hydride), metal hydrogen complex compounds (e.g. sodium trimethoxyborohydride), boranes (e.g. boron tribromide) or hydrazines to a chlorine-based substrate resin such as polyvinyl chloride or polyvinylidene chloride.

Reaction of Arylethanals with Boron Tribromide.

Abstract: Treatment of arylethanals 1 with boron tribromide give 2-phenylnaphthalenes 2 or 1,2,9,10-tetrahydro-1,9-epoxydibenzo[a,e]cyclooctenes 3 by a tandem aldol condensation-intramolecular Friedel-Crafts cyclization or a condensation at the O-position followed by a double Friedel-Crafts alkylation respectively. In all cases, a total demethylation of the methoxy groups occurs.

The Reaction of Arylacetones with Boron Tribromide.

Abstract: Treatment of arylacetones 1 with boron tribromide gives 1,3-dimethyl-2-arylnaphthalenes 3 in fair to good yields by a tandem aldol condensation-intramolecular cyclization. This reaction is limited to the electron-rich arylacetones. In the case of methoxyphenylacetones, a demethylation occurs leading to 1,3-dimethyl-2-hydroxyphenylnaphthols. Other cyclization may occur for orthomethoxyphenylacetones leading to intramolecular acetal 4b or 5-, 6or 7-hydroxy-2-methylbenzo[b]furans 6n–p. In the case of the 1-naphthylacetone, a bromination reaction of the phenanthrene 3i occurs leading to bromophenanthrene 5i.

Novel Applications of Alkyl Fluorides in Organic Synthesis: Versatile Nitrogen Protecting Groups.

Abstract: The potential of the 2-fluoroethyl group as a nitrogen protecting group was demonstrated. The stability of alkyl fluorides, such as 2-fluoroethyl, to a variety of reaction conditions, makes them attractive nitrogen protecting groups. The 2-fluoroethyl group was easily introduced, in good yields, by the treatment of the NH group with potassium carbonate and 2-bromo-1-fluoroethane. Reaction of the 2-fluoroethyl group with boron tribromide resulted in the replacement of fluorine by bromine, to give the corresponding 2-bromoethyl group which was easily removed by known methods.

Synthesis of 4,6-Difluoro-5-hydroxy-(α-methyl)tryptamine and 4,6-Difluoro-5-hydroxy-(β-methyl)tryptamine as Potential Selective Monoamine Oxidase B Inhibitors.

Abstract: Condensation of 4-nitro-1-pentanal and 4-nitropentanal 3-methylbutanal with 3,5-difluoro-4-methoxyphenylhydrazine afforded 4,6-difluoro-5-methoxy-3-(2′-nitro)propylindole 4a and 4,6-difluoro-5-methoxy-3-(1′-methyl-2′-nitro)ethylindole 4b , respectively, in one step. Reduction of the nitro group with lithium aluminum hydride followed by removal of the methyl ether with boron tribromide produced the title compounds. They were inactive as MAO B inhibitors.