Solution-phase parallel synthesis of carbamates using polymer-bound N-hydroxysuccinimide

[formula: see text] A convenient method for the synthesis of carbamates using polymer-supported N-hydroxysuccinimide is described. Various carbamates were synthesized in highly pure form without the need for chromatographic purification. This new "catch and release"-type solid-phase synthesis should be useful for combinatorial synthesis of various carbamates.     

A turbidimetric method for colloid titrations

Positive colloid solutions can be titrated with the polyanion potassium polyvinylsulfate with toluidine blue as indicator, but negative colloid solutions must be treated with an excess of the polycation polydiallyldimethylammonium chloride which is backtitrated with potassium polyvinylsulfate. By turbidimetry however, positive or negative colloid solutions can be directly titrated with, respectively, the polyanionic or polycationic titrant. Two methods, the construction and differential methods, can be used. The latter method is particularly useful when a flocculent precipitate appears during the titration.     

Synthesis and DNA strand breakage activity of some 1,4-diazepines

Reactions of 1,3-propanediamine with alpha-dicarbonyl compounds (1a-e) were examined and various condensed heterocyclic compounds such as 1,4-diazepines (2) and 3-pyrimidine derivatives (3) were obtained. Some of 1,4-diazepines (2) showed DNA strand breakage activity.     

Long branching in poly(vinyl acetate) and poly(vinyl alcohol). II. Polymerization of vinyl acetate in the presence of crosslinked poly(vinyl alcohol)

It is a common view that poly(vinyl acetate) has many branches at the acetyl side group, but that the corresponding poly(vinyl alcohol) has little branching. In order to study the branching in poly(vinyl acetate) and poly(vinyl alcohol) which is formed by chain transfer to polymer, the polymerization of ¹⁴C-labeled vinyl acetate in the presence of crosslinked poly(vinyl acetate), which was able to be decrosslinked to give soluble polymers, was investigated at 60°C and 0°C. This system made it possible to separate as well as to distinguish the graft polymer from the newly polymerized homopolymer. Furthermore, the degree of grafting onto the acetoxymethyl group and onto the main chain were estimated. It became clear that, in the polymerization of vinyl acetate, chain transfer to the polymer main chain takes place about 2.4 times as frequently at 60°C as that to the acetoxy group and about 4.8 times as frequently at 0°C.     

Chemoenzymatic synthesis of n-hexyl and O-beta-D-xylopyranosyl-(1-->6)-beta-D-glucopyranosides

Direct beta-glucosidation between 1,6-octanediol (5) and D-glucose (3) using the immobilized beta-glucosidase (EC 3.2.1.21) from almonds with the synthetic prepolymer ENTP-4000 gave a mono-beta-glucoside (6) in 61.4% yield, which was converted into the n-hexyl beta-D-glucopyranoside (1) by means of a chemoenzymatic method. The coupling of the n-hexyl beta-D-glucopyranoside congener (13) and 2,3,4-tri-O-acetyl-beta-D-xylosyl congener (14), followed by deprotection, afforded the synthetic n-hexyl O-beta-D-xylopyranosyl-(1-->6)-beta-D-glucopyranoside (2), which was identical to the natural 2 with respect to the spectral data and specific rotation.     

New direction in organopalladium chemistry: structure and reactivity of unsaturated hydrocarbon ligands bound to multipalladium units

Examination of the manner of interaction between Pd(0) and allylpalladium(II) complexes, both being involved as key intermediates in Pd-catalyzed allylic coupling, led us to discover a new role for such combinations in affecting the stereochemistry of the transformations. A similar investigation of the system involving Pd(0) and allenyl/propargyl complexes of Pd(II) led to the discovery of dinuclear Pd(I)bond;Pd(I) complexes containing bridging allenyl/propargyl ligands, which exhibited novel structural and reactivity aspects of great synthetic significance. A systematic comparison was made between the structure, stability, and reactivity of allyl and allenyl/propargyl ligands in dinuclear complexes and those in mononuclear counterparts. On the basis of MO calculations, coordination behavior specific to the ligands of the dinuclear complex is attributed to the occurrence of the back-donating interaction from filled Pdbond;Pd bonding orbitals to vacant ligand pi* orbitals. Similar bonding features are the origin of the ready synthesis of novel one-dimensional sandwich complexes composed of conjugated polyene ligands and linear polypalladium chains. A substitutionally labile dipalladium complex reacts with an equimolar amount of trienes or alkynes to give formal [4pi + 2sigma] or [2pi + 2sigma] adducts, respectively, which undergo further unique transformations with additional unsaturated substrates.     

Triple tandem catalyst mixtures for the synthesis of polyethylenes with varying structures

Tandem catalysis in a single medium presents challenges and opportunities for creating novel synthetic protocols. Thus far, only two homogeneous catalysts have been used in tandem. Herein, we report that it is possible to coordinate the action of three well-defined homogeneous catalysts to produce a wide range of branched polyethylenes from a single monomer. Thus, ([(eta(5)-C(5)Me(4))SiMe(2)(eta(1)-NCMe(3))]TiMe)(MeB(C(6)F(5))(3)) (1), [(C(6)H(5))(2)PC(6)H(4)C(OB(C(6)F(5))(3))O-kappa(2)P,O]Ni(eta(3)-CH(2)C(6)H(5)) (2), and ((H(3)C)C[N(C(6)H(5))]C[O-B(C(6)F(5))(3)][N(C(6)H(5))]-kappa(2)N,N)Ni(eta(3)-CH(2)C(6)H(5)) (3) react with ethylene to produce branched polyethylene with structures that cannot be obtained using a single- or a two-component catalyst combination. The properties of the polyethylene depend on the ratio of the three catalysts. High-throughput screening techniques proved essential for optimizing reaction conditions and for probing how the catalyst composition influences the polymer properties.     

Stepwise growth of polypalladium chains in 1,4-diphenyl-1,3-butadiene sandwich complexes

A series of 1,4-diphenyl-1,3-butadiene multinuclear palladium sandwich complexes are synthesized by stepwise growth of palladium chains within a sandwich framework.     

Regio- and stereoselective synthesis of allylsilanes using (methylphenylamino) tributylphosphonium iodine

Regio- and stereoselective synthesis of variously substituted allylsilanes is achieved by organocuprate-mediate γ-coupling of allylic alcohols using the title reagent ($\text{1}$).