Decarbonylative ether dissection by iridium pincer complexes

A unique chain-rupturing transformation that converts an ether functionality into two hydrocarbyl units and carbon monoxide is reported, mediated by iridium(i) complexes supported by aminophenylphosphinite (NCOP) pincer ligands. The decarbonylation, which involves the cleavage of one C–C bond, one C–O bond, and two C–H bonds, along with formation of two new C–H bonds, was serendipitously discovered upon dehydrochlorination of an iridium(iii) complex containing an aza-18-crown-6 ether macrocycle. Intramolecular cleavage of macrocyclic and acyclic ethers was also found in analogous complexes featuring aza-15-crown-5 ether or bis(2-methoxyethyl)amino groups. Intermolecular decarbonylation of cyclic and linear ethers was observed when diethylaminophenylphosphinite iridium(i) dinitrogen or norbornene complexes were employed. Mechanistic studies reveal the nature of key intermediates along a pathway involving initial iridium(i)-mediated double C–H bond activation.

A unique chain-rupturing transformation that converts an ether functionality into two hydrocarbyl units and carbon monoxide is reported.     

Control of competing N-H insertion and Wolff rearrangement in dirhodium(II)-catalyzed reactions of 3-indolyl diazoketoesters. synthesis of a potential precursor to the marine 5-(3-indolyl)oxazole martefragin A

Dirhodium(II)-catalyzed reaction of 3-indolyl alpha-diazo-beta-ketoester 25 in the presence of hexanamide results in competing metal carbene N-H insertion and Wolff rearrangement. The corresponding phenyl diazoketoester 32, on the other hand, gives only the product of N-H insertion, suggesting that the indole moiety is more prone to 1,2-rearrangement. The competing processes were investigated in a range of 3-indolyl alpha-diazo-beta-ketoesters (36, 38, 40, 44); these studies established that the Wolff rearrangement could be effectively suppressed by the presence of a strong electron-withdrawing group on the indole nitrogen. Dirhodium(II) catalysts were also more effective than copper or Lewis acid catalysts in favoring the insertion process. The products of N-H insertion, the ketoamides (26, 47, 49, 51, 53), were readily cyclodehydrated to the corresponding 5-(3-indolyl)oxazoles. The N-H insertion/cyclodehydration methodology was used in a formal synthesis of the marine natural product martefragin A. Thus the N-Boc homoisoleucine amide 23, prepared by asymmetric hydrogenation of a dehydro amino acid, underwent N-H insertion with the rhodium carbene derived from the N-nosyl indolyl diazoester 40, followed by cyclodehydration and deprotection to give the 5-(3-indolyl)oxazole martefragin A precursor 75.     

Hydration and dielectric properties of aqueous solutions of protonated diallylmethylammonium polymer: transition from monomer to polymer

Abstract

The high-frequency dielectric relaxation of aqueous solutions of protonated diallylammonium polyelectrolyte, namely poly(diallylmethylammonium trifluoroacetate) has been studied at the maximum water dispersion frequencies, 7.5–25?GHz, and temperatures of 288, 298, and 308?K. Dielectric relaxation parameters have been calculated and compared with similar characteristics of aqueous solutions of monomer, diallylmethylammonium trifluoroacetate, and pyrrolidinium trifluoroacetate salt simulated structure of pyrrolidinium polymer link. It has been concluded that although the monomer features hydrophobic hydration, its polymer exhibits hydrophilic hydration properties. This change is related to conformation of hydrophilic-hydrophobic polycations in aqueous solutions and the change in the structure of polymer links.     

Reactions of Allyl Alcohols of the Pinane Series and of Their Epoxides in the Presence of Montmorillonite Clay

The reactivity of allyl alcohols of the pinane series and of their epoxides in the presence of montmorillonite clay in intra‐ and intermolecular reactions was studied. Mutual transformations of (+)‐trans‐pinocarveol ((+)‐ 2 ) and (?)‐myrtenol ((?)‐ 3a ) were major reactions of these compounds on askanite–bentonite clay (Schemes 1 and 2). However, the two reactions gave different isomerization products, indicating that the reactivity of the starting alcohol (+)‐ 2 or (?)‐ 3a was different from that of the same compound (+)‐ 2 or (?)‐ 3 formed in the course of the reactions. (?)‐cis‐ and (+)‐trans‐Verbenol ((?)‐ 16 and (+)‐ 12 , resp.), as well as (?)‐cis‐verbenol epoxide ((?)‐ 20 ) reacted with both aliphatic and aromatic aldehydes on askanite–bentonite clay giving various heterocyclic compounds (Schemes 4, 5 and 7); the reaction path depended on the structure of both the terpenoid and the aldehyde.     

Visualization and characterization of electroactive defects in the native oxide film on aluminium

Spatial!y localized electrochemical activity at Al/Al2O3 electrodes has been investigated using scanning electrochemical microscopy (SECM) in order to establish the relationship between localized corrosion of Al (and Al alloys) with the defect structure of the native Al2O3 film. Local electron transfer at microscopic defects (2 to 50 microm radius) was visualized in acetonitrile solutions using the nitrobenzene/nitrobenzene radical anion (Eo approximately -1.6 V vs. Ag/Ag+) and tetracyanoquinodimethane/tetracyanoquinodimethane radical anion couples (Eo approximately -0.3 V) as redox mediators for imaging. SECM investigations revealed no significant differences in electrochemical activity at Al/AI203 electrodes in the two mediator solutions, indicating that electrical conduction at the defect sites is weakly dependent on interfacial potential and the electric field across the Al2O3 film. The density of electroactive defects observed by SECM varied by 2 to 3 orders of magnitude between electrodes prepared from the same source of Al (either 99.450% and 99.9995%) suggesting that electrical conduction in the native oxide is very sensitive to surface preparation. Defect densities as low as approximately 3 sites cm(-2) were readily measured by SECM.     

Fluorophore-quencher distance correlation functions from single-molecule photon arrival trajectories

We generalize and simplify the method of Yang and Xie (J. Chem. Phys. 2002, 117, 10965) to obtain distance correlation functions from photon arrival trajectories of single fluorophores whose lifetime, [k(r)](-1), depends on the distance to a quencher. It is assumed that this distance does not change during the fluorescence lifetime. The experimental trajectory is first transformed by replacing the delay time (i.e., the interval between the photon arrival and the nearest laser pulse) by a certain function of this delay time. This function is the inverse Laplace transform of r(k), which is the solution of k(r) = 1. The correlation function of the transformed data then directly gives the distance correlation function. Illustrative examples include F?rster energy transfer and quenching due to electron transfer.     

Synthesis of monodisperse polymers from proteins

Proteins are functional biopolymers; viewed as molecules, they are also monodisperse polyamides with chemically reactive side chains. This paper describes the use of proteins as starting materials for the synthesis of monodisperse polymers with nonbiological functionalities attached to the side chains. It demonstrates the complete derivatization of amine groups (lysine side chains and N-termini) on three different proteins by addition of activated carboxylate reagents in aqueous solutions containing sodium dedecyl sulfate (SDS), under denaturing conditions. Several different acylating reagents were used to generate derivatized proteins; the resulting compounds constitute a new class of monodisperse, semisynthetic polymers, having the potential for wide variation in the structure of the backbone and of the side chains. Modification of lysozyme on a gram scale demonstrated that the method can generate useful quantities of material.     

Ate complexes of Ge(II) and Sn(II) with bidentate ligands [LiE(OCH2CH2NMe2)3]2 (E=Ge, Sn): synthesis and structure

The reaction of equimolar quantities of LiOCH₂CH₂NMe₂ and E¹⁴(OCH₂CH₂NMe₂)₂ (E¹⁴=Ge, Sn) in ether yielded new ate complexes [LiE¹⁴(OCH₂CH₂NMe₂)₃]₂ (E¹⁴=Ge (1), Sn (2)) with bidentate ligands. The compounds 1 and 2 are white crystalline substances which are highly soluble in THF and pyridine and very sensitive to the traces of oxygen and moisture. The structures of these compounds are studied by X-ray diffraction analysis. The ate complexes 1 and 2 are powerful nucleophiles and may be employed as ligands (neutral) in the coordination chemistry of the transition metals. The electronegative O-substituents at the divalent E¹⁴ atoms render them less oxidizable than alkyl- or aryl-substituted derivatives, and the bidentate ligands, owing to intramolecular donor-acceptor interactions, make them more thermodynamically stable compared to monodentate ligands.     

Evidence for specific solvation of two halocarbene amides

Laser flash photolysis (LFP, 308 nm) of endo-10-halo-10'-N,N-dimethylcarboxamidetricyclo[4.3.1.0]-deca-2,4-diene (1Cl and 1F) releases indan and halocarbene amide (2Cl and 2F). Although the carbenes are not UV-vis active, they react rapidly with pyridine to form ylides (4Cl, 4F), which are readily detected in LFP experiments (lambda(max) = 450 nm). Dioxane decreases the observed rate of carbene reaction with pyridine in CF(2)ClCFCl(2). Small amounts of THF decrease the observed rate of reaction of carbene 2F with pyridine but increase the rate of reaction of carbene 2Cl with pyridine. LFP (266 nm) of dienes 1Cl and 1F in CF(2)ClCFCl(2) with IR detection produces carbenes 2Cl and 2F with carbonyl vibrations at 1635 and 1650 cm(-1), respectively. In dioxane or THF solvent, LFP produces the corresponding ether ylides (5Cl, 5F) by capture of carbenes 2Cl and 2F. The ylides have broad carbonyl vibrations between 1560 and 1610 cm(-1). The addition of a small amount of dioxane in CFCl(2)CF(2)Cl extends the lifetime of the carbene. This observation, together with the ether-induced retardation of the rates of carbene capture by tetramethylethylene and pyridine, is evidence for solvation of the carbene by dioxane.     

Diterpenoid Alkaloids of Delphinium buschianum Grossh.

From the aerial parts of Delphinium buschianum Grossh ., collected in Turkey, a new diterpenoid alkaloid 1 , named budelphine, was isolated along with the known diterpenoid alkaloids karakoline ( 2 ), 18‐hydroxy‐14‐O‐methylgadesine ( 3 ), delsoline ( 4 ), lapaconidine ( 5 ), columbianine ( 6 ), 14‐benzoylneoline ( 7 ), and hetisine ( 9 ). The structure of 1 was established on the basis of ¹H‐, ¹³C‐, DEPT, ¹H,¹H‐COSY, NOESY, HSQC, and HMBC NMR studies.