Diasteroselective Addition of Monoand Bis-Silylphosphines to Chiral Aldehydes

Abstract

The addition of silylphosphines to chiral aldehydes proceeds with high diastereoselectivity to give optically pure tertiary α -trimethylsiloxyalkylphosphines. The diastereomeric excesses of the addition products were achieved to 90–100%. The reaction of bis(trimethylsilyl)phenylphosphine with the acetonide of (R)-glyceraldehyde provides diastereomerically enriched tertiary bis(glyceryl)phosphines.     

SYNTHESIS AND CONFORMATIONAL STUDIES OF A NUMBER OF SATURATED BICYCLIC SIX-MEMBERED RING PHOSPHITES

Abstract

An ¹H NMR study of the conformation of the dioxaphosphorinane ring of a number of diastereoisomeric bicyclic saturated six-membered ring phosphites (3ab-10ab) has been performed. The dioxaphosphorinane ring of these phosphites is transannelated with a tetrahydrofuran, cyclopen-tane, tetrahydropyran or cyclohexane ring. The substituent on the phosphorus atom is a methoxy or phenoxy group. It is shown that the cis isomers 3a-10a prefer a chair conformation of the dioxaphosphorinane ring, independent of the substituent on the phosphorus atom and of the nature of the transannelated ring. In contrast, for the trans isomers 3b-10b a twist rather than a chair conformation of the dioxaphosphorinane ring is preferred. The fraction of the twist conformer in the trans isomers is mainly determined by the substituent on phosphorus. The size and composition of the transannelated ring are relatively unimportant in this respect. For both cis and trans isomers the preferred geometry is solvent-independent. The measured ^3JPOCH couplings of the cis isomers 3a-10a are used to formulate an expression for the dependence of such couplings upon dihedral angles in bicyclic phosphites.     

Oxidative Stabilization of Poly(norbornene) Polymers Prepared by Ring Opening Metathesis Polymerization

Polymers prepared by ring opening methathesis polymerization contain double bonds along the backbone and are susceptible to oxidation during high temperature processing or device operation. To overcome this, we report a simple method to improve the oxidative stability of ROMP based polymers by inclusion of a small percentage of monomer functionalized with a radical scavenger in the feedstock. The oxidation induction temperature was improved from 111°C up to 262°C when 8 mol% of the functionalized comonomer was included in the feedstock. Modest improvements in the thermal decomposition temperature were also observed.     

Ionic Copolymerizations

It is shown that for the reported instances of “random” copolymerization in cationic systems, N values related to relative reactivity may be derived for monomers. The N values approximate reasonably well the values of the function, exp (-e) - 1.23, where e is the polarity e of the Q-e scheme for free-radical copolymerizations.

In a recent paper [1] it was shown that for the reported instances [2-4] of “random” copolymerization (r₁,r₂ = 1) in cationic systems, N values, related to relative reactivity, might be derived for monomers, employing styrene as a base monomer (N = 1). Thus d[M₁]/d[M₂] =N₁[M₁]/N₂[M₂] (1)

where d[M₁]/d[M₂] is the instantaneous copolymer composition, [M₁]/[M₂] is the ratio of unreacted monomers, and N₁ and N₂ are parameters related to general monomer reactivity of monomers 1 and 2, respectively, in cationic copolymerization.     

Synthesis and Reaction of Some Indenopyridine and Thieno[2,3-b]Indeno[2,1-e]Pyridine Derivatives

Synthesis of indenopyridine-2-thione derivatives 6a-e via reaction of compound 1 with thioamides 2a-e in good yields. Several thieno[2,3-b]indeno[2,1-e]pyridine 9a-e have been synthesized. Some of them was used as a key intermediate in synthesis of 10-12. On the other hand, compound 1 reacted with various reagents to yield 16, 19, 21-24.     

Synthesis and Properties of Surfactants derived from N‐Acetyl‐D‐Glucosamine

The synthesis of 2‐acetamido‐2‐deoxy‐6‐O‐octanoyl‐D‐glucono‐1,5‐lactone 9 and 2‐acetamido‐2‐deoxy‐6‐O‐octanoyl‐α‐D‐glucopyranose 7 from 2‐acetamido‐2‐deoxy‐α‐D‐glucopyranose is reported. For both targets, the key intermediate was allyl 2‐acetamido‐3,4‐di‐O‐benzyl‐2‐deoxy‐6‐O‐octanoyl‐α‐D‐glucopyranoside 5. Surface tension measurements (critical micellar concentration of 22.3 mM and 5 mM for 9 and 7, respectively) showed up the surface activity of both compounds, while enzyme inhibition assays indicated that 9 could inhibit bovine β‐N‐acetylglucosaminidase (K_i=6.5 µM) but not Serratia marcescens chitobiase nor hen egg‐white lysozyme. Moreover, 7 was shown to induce chitinase production of S. marcescens and to be readily metabolized by these bacteria.      

Substituent Effects on Oxidation‐Induced Formation of Quinone Methides from Arylboronic Ester Precursors

A series of arylboronic esters containing different aromatic substituents and various benzylic leaving groups (Br or N⁺Me₃Br^?) have been synthesized. The substituent effects on their reactivity with H₂O₂ and formation of quinone methide (QM) have been investigated. NMR spectroscopy and ethyl vinyl ether (EVE) trapping experiments were used to determine the reaction mechanism and QM formation, respectively. QMs were not generated during oxidative cleavage of the boronic esters but by subsequent transformation of the phenol products under physiological conditions. The oxidative deboronation is facilitated by electron‐withdrawing substituents, such as aromatic F, NO₂, or benzylic N⁺Me₃Br^?, whereas electron‐donating substituents or a better leaving group favor QM generation. Compounds containing an aromatic CH₃ or OMe group, or a good leaving group (Br), efficiently generate QMs under physiological conditions. Finally, a quantitative relationship between the structure and activity has been established for the arylboronic esters by using a Hammett plot. The reactivity of the arylboronic acids/esters and the inhibition or facilitation of QM formation can now be predictably adjusted. This adjustment is important as some applications may benefit and others may be limited by QM generation.     

Kinetic Behavior of Quaternary Ammonium Hydroxides in Mixed Methane and Carbon Dioxide Hydrates

This study evaluates the kinetic hydrate inhibition (KHI) performance of four quaternary ammonium hydroxides (QAH) on mixed CH₄ + CO₂ hydrate systems. The studied QAHs are; tetraethylammonium hydroxide (TEAOH), tetrabutylammonium hydroxide (TBAOH), tetramethylammonium hydroxide (TMAOH), and tetrapropylammonium hydroxide (TPrAOH). The test was performed in a high-pressure hydrate reactor at temperatures of 274.0 K and 277.0 K, and a concentration of 1 wt.% using the isochoric cooling method. The kinetics results suggest that all the QAHs potentially delayed mixed CH₄ + CO₂ hydrates formation due to their steric hindrance abilities. The presence of QAHs reduced hydrate formation risk than the conventional hydrate inhibitor, PVP, at higher subcooling conditions. The findings indicate that increasing QAHs alkyl chain lengths increase their kinetic hydrate inhibition efficacies due to better surface adsorption abilities. QAHs with longer chain lengths have lesser amounts of solute particles to prevent hydrate formation. The outcomes of this study contribute significantly to current efforts to control gas hydrate formation in offshore petroleum pipelines.     

Laser ion source activities at Brookhaven National Laboratory

In Brookhaven National Laboratory (BNL), we have been developing laser ion sources for diverse accelerators. Tabletop Nd:YAG lasers with up to several Joules of energy are mainly used to create ablation plasmas for stable operations. The obtained charge states depend on laser power density and target species. Two types of ion extraction schemes, direct plasma injection scheme (DPIS) and conventional static extraction, are used depending on the application. We optimized and selected a suitable laser irradiation condition and a beam extraction scheme to meet the requirement of the following accelerator system. We have demonstrated to accelerate more than 5?×?10¹⁰ of C⁶⁺ ions using the DPIS. We successfully commissioned a low-charge ion beam provider to the user facilities in BNL. To achieve higher current, higher charge state and lower emittance, further studies will continue.     

Reception pattern influence on magnetoacoustic tomography with magnetic induction

Based on the acoustic radiation theory of a dipole source,the influence of the transducer reception pattern is studied for magnetoacoustic tomography with magnetic induction(MAT-MI).Numerical studies are conducted to simulate acoustic pressures,waveforms,and reconstructed images with unidirectional,omnidirectional,and strong directional transducers.With the analyses of equivalent and projection sources,the influences of the model dimension and the layer effect are qualitatively analyzed to evaluate the performance of MAT-MI.Three-dimensional simulation studies show that the strong directional transducer with a large radius can reduce the influences of equivalent sources,projection sources,and the layer effect effectively,resulting in enhanced pressure and improved image contrast,which is beneficial for boundary pressure extraction in conductivity reconstruction.The reconstructed conductivity contrast images present the conductivity boundaries as stripes with different contrasts and polarities,representing the values and directions of the conductivity changes of the scanned layer.The favorable results provide solid evidence for transducer selection and suggest potential practical applications of MAT-MI in biomedical imaging.