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Results for “Vinyl Compounds”

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At least 343 records · Page 19Linked to original sources
PubMed2006

Palladium-catalyzed asymmetric allylic alkylation of meso- and dl-1,2-divinylethylene carbonate.

The palladium-catalyzed asymmetric allylic alkylation of a 1:1 mixture of dl- and meso-1,2-divinylethylene carbonate is reported. For the first time, both the ionization and nucleophilic addition steps of the catalytic cycle act as enantiodiscriminating steps to give a single product in high enantiomeric excess. The reactions proceed in >98% ee to efficiently generate useful chiral building blocks from acrolein. The absolute and relative configurations of iso-cladospolide B and 11-epi-iso-cladospolide B were verified by total synthesis, solving an apparent discrepancy in the literature.

Alcohols↗
PubMed2005

New highly nucleophilic and practically accessible chlorocarbenoids for carbonyl olefination.

[reaction: see text] Direct oxidative addition of CHCl3 to the Mg-TiCl4 bimetallic species resulted in the generation of a highly nucleophilic and practically convenient chloromethylenetitanium complex, which efficiently effected condensation even with enolizable or inert carbonyl compounds, such as sterically congested ketones, to provide vinyl chloride compounds.

Journal Article↗
PubMed2005

Highly regio- and stereoselective hydrostannylation of alkynols with a new Lewis acidic hydrostannane.

[reaction: see text] Bu2Sn(OTf)H (1a), easily prepared from Bu2SnH2 and TfOH, was found to be very valuable for highly regio- and stereoselective hydrostannylation of various propargyl alcohols leading to (Z)-gamma-stannylated allyl alcohols. The stannylation with 1a is applicable to the synthesis of hydroxy-substituted (Z)-vinylstannanes from terminal alkynes bearing a hydroxy group at the homoallylic or bishomoallylic position. The coordination of the hydroxy group to the Lewis acidic tin center plays an important role for the observed regio- and stereochemistry.

Allyl Compounds↗
PubMed2005

Synthesis of 3,4-dihydro-2H-pyrans by hetero-Diels-Alder reactions of functionalized alpha,beta-unsaturated carbonyl compounds with N-vinyl-2-oxazolidinone.

Cycloadditions of 3-aryl-2-benzoyl-2-propenenitriles and 3-phenylsulfonyl-3-buten-2-one to N-vinyl-2-oxazolidinone proceed regio- and diastereoselectively yielding cis and trans diastereoisomers of 4-aryl-3,4-dihydro-2-(2-oxo-3-oxazolidinyl)-2H-pyrans in 37-65% yield. Cycloadducts cis- were the major products. Reaction of 5-arylidene-1,3-dimethylbarbituric acids with dienophile afforded mixtures of 2H-pyrano[2,3-d]pyrimidine-2,4(3H)-diones trans and products resulted from an elimination of 2-oxazolidinone, in 50-52% yield. To confirm the experimental results, semiempirical AM1 and PM3 calculations of frontier orbital energies have been performed.

Cyclization↗
PubMed2000

Synthesis and radical reaction of 1'-phenylselenonucleosides.

The 1'alpha-phenylselenouridine derivative (4) was successfully synthesized via enolization at the 1'-position of the 3',5'-O-TIPDS-2'-ketouridine (1). After the introduction of a vinylsilyl tether as an intramolecular radical acceptor at the 2'-hydroxy group of 4, its atom-transfer radical cyclization reaction, followed by the treatment with TBAF gave 1'alpha-vinyluridine derivative (10). Using this procedure, 1'alpha-vinyluridine (11) and -cytidine (14) were successfully synthesized.

Cytidine↗
PubMed1994

Method for reducing scatter radiation dose to the contralateral breast during tangential breast irradiation therapy.

PURPOSE: To reduce scatter dose to the contralateral breast during tangential breast irradiation therapy. MATERIALS AND METHODS: The authors used a 4-mm-thick commercially available vinyl-coated flexible lead shield that contains a compound of vinyl resin and lead powder of 1-mm-equivalent lead density. Contralateral scatter dose was measured at 5 cm outside the geometric field edge and along the field axis, with and without use of block trays and different wedges. RESULTS: On the skin, contralateral scatter dose from the medial tangential beam was reduced from about 15% to about 5% of the therapeutic dose delivered to the treated breast. The bulk of scatter dose was absorbed within the first 2 cm of breast tissue. CONCLUSION: Reduction in unwanted scatter dose to the contralateral breast is in accord with the philosophy of keeping radiation exposure as low as reasonably achievable and might be of most benefit for young patients.

Breast↗
PubMed2003

[Studies of poly(vinyl alcohol)/hydroxylapatite hydrogels compounds for cartilage implantation].

The structures and properties of polyvinyl alcohol (PVA)/hydroxylapatite(HA) composites were investigated. The components and processing conditions were studied for preparation of optimum compound hydrogels with good lubricating feature and high bioactivity. The properties, such as stretch strength, compress strength, friction, compress stress relaxation of various compound hydrogels were compared. The micro-morphology of PVA hydrogels and PVA/HA hydrogels were investigated by use of SEM. It was found that the addition of HA could improve the lubricating feature and mechanical strength of hydrogels, and its compress stress relaxation properties were closer to those of natural cartilages.

Biocompatible Materials↗
PubMed2002

Preparation of polymer-supported benzyllithium reagents.

Cross-linked polystyrenes (2, 8, and 11) possessing pendant double bonds conjugated with benzene ring were prepared by both polymerization method and chemical modification of pre-formed polymers. These double bonds were readily lithiated with n-butyllithium to give the benzyllithium species on the polymer. The polymer supported benzylic anions (3 and 12) are a versatile polymeric organometallic reagent that reacted with various kinds of electrophiles.

Anions↗
PubMed2003

A catalytic asymmetric method for the synthesis of gamma-unsaturated beta-amino acid derivatives.

Catalytic enantioselective synthesis of beta-amino acid derivatives is an area of intense interest, due to the importance of these compounds as components in pharmaceutical agents and peptidomimetics. In this report, we present the first catalytic enantioselective method for the synthesis of gamma-unsaturated beta-amino acids and their corresponding 1,3-amino alcohol derivatives. This methodology takes advantage of a highly enantioselective vinylzinc addition to an aldehyde to set chirality. The resulting allylic alcohols are then transformed into the corresponding allylic amines via Overman's [3,3]-sigmatropic imidate rearrangement, and subsequent one-pot deprotection-oxidation of a pendant oxygen leads to the gamma-unsaturated beta-amino acid derivatives of high enantiopurity.

Aldehydes↗