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Your search keyword '"Rudolph K"' showing total 18 results
Start Over Author "Rudolph K" Journal journal of the american chemical society
18 results on '"Rudolph K"'

1. Use to effect regiospecific control

Author

Johnson, William S., Buchanan, Robert A., Bartlett, William R., Tham, Fook S., and Kullnig, Rudolph K.

Subjects
Fluorine -- Usage, Cations -- Research, Ring formation (Chemistry) -- Research, Chemistry
Abstract

The use of fluorine atom for achieving regiospecific control over the ring closures of tertiary bicyclic cations is demonstrated. The rearrangement of fluorine-synthesized cyclopentenols are studied to establish the stereochemistry of their tetrasubstituted fluoro alkene bonds. Results show that the fluorine atom is capable of controlling the regiochemistry to produce a stable product with a 6-membered ring.

Published
1993

2. Asymmetric synthesis of a steroid

Author

Johnson, William S., Fletcher, Vernon R., Chenera, Balan, Bartlett, William R., Tham, Fook S., and Kullnig, Rudolph K.

Subjects
Fluorine -- Usage, Ring formation (Chemistry) -- Research, Cations -- Research, Steroids (Drugs) -- Research, Chemistry
Abstract

The use of the fluorine atom as a cation-stabilizing agent for enhancing polyene cyclizations is demonstrated. A cyclization substrate is synthesized both in the racemic and optically active acetal forms. The quarternary fluorine atom is then deposited at pro-C-8 by hydrogen stereoselectivity with retention of configuration. Results show that the cyclization of the acetal gives a substantial yield of fluorotetracycle which can be converted into a known steroid type.

Published
1993

3. Background and exploratory experiments

Author

Johnson, William S., Chenera, Balan, Tham, Fook S., and Kullnig, Rudolph K.

Subjects
Fluorine -- Usage, Ring formation (Chemistry) -- Research, Cations -- Research, Chemistry
Abstract

A new method for the stereoselective synthesis of polyenic cyclization substrates is presented. The method replaces the vinyl hydrogen of an E-trisubstotuted olefinic bond with a fluorine atom. This approach enhances the formation of polycyclic products as the vinyl fluoride function has been proven to be a good terminator of polyene cyclizations. It also allows the performance of reactions under very mild conditions resulting in high-yield crystallizations.

Published
1993

4. Solid-state photochemistry. Remarkable effects of the packing of molecules in crystals on the diastereoselectivity of the intramolecular 2+2 photocycloaddition of a 4-(3'-butenyl)-2,5-cyclohexadien-1-one

Author

Schultz, Arthur G., Taveras, Arthur G., Taylor, Richard E., Tham, Fook S., and Kullnig, Rudolph K.

Subjects
Crystals -- Research, Ring formation (Chemistry) -- Research, Stereochemistry -- Research, Chemistry
Abstract

A study was done on an asymmetric control involving photochemistry of a 4-(3'-butenyl)-2,5-cyclohexadien-1-one in the solid state. It was shown that that competing and nearly isoenergetic unimolecular photocycloadditions can be selectively partitioned in the solid state as a result of the availability of effective reaction volumes. Installation of a chiral auxiliary provides an opportunity for desymmetrization of the 2,5-cyclohexadien-1-one ring.

Published
1992

5. Cation-stabilizing auxiliaries in polyene cyclizations. 4. The fluorine atom as a cation-stabilizing auxiliary in biomimetic polyene cyclizations. 1. Background and exploratory experiments

Author

Fook S. Tham, William S. Johnson, Balan Chenera, and Rudolph K. Kullnig

Subjects
Chemistry, Acetal, chemistry.chemical_element, General Chemistry, Polyene, Biochemistry, Catalysis, Claisen rearrangement, chemistry.chemical_compound, Colloid and Surface Chemistry, Polymer chemistry, Fluorine, Molecule, Stereoselectivity, Aliphatic compound
Abstract

With the aim of testing the fluorine atom as a potential cation-stabilizing (C-S) auxiliary for enhancing polyene cyclizations, new methodology has been developed for the stereoselective synthesis of polyenic cyclization substrates in which the vinyl H of an E-trisubstituted olefinic bond is replaced by F

Published
1993

6. Cation-stabilizing auxiliaries in polyene cyclizations. 5. The fluorine atom as a cation-stabilizing auxiliary in biomimetic polyene cyclizations. 2. Asymmetric synthesis of a steroid

Author

Balan Chenera, Rudolph K. Kullnig, Vernon R. Fletcher, William S. Johnson, William R. Bartlett, and Fook S. Tham

Subjects
chemistry.chemical_classification, Ketone, Chemistry, medicine.medical_treatment, Acetal, Enantioselective synthesis, chemistry.chemical_element, General Chemistry, Polyene, Biochemistry, Combinatorial chemistry, Catalysis, Steroid, chemistry.chemical_compound, Colloid and Surface Chemistry, medicine, Fluorine, Molecule, Aliphatic compound
Abstract

The use of the fluorine atom an a cation-stabilizing (C-S) auxiliary for enhancing polyene cyclization has been improved in synthetic effectiveness by the demonstration that an acetal 5 can be converted to a racemic fluorocycle, bearing the natural backbone configuration of the steroids

Published
1993

7. Cation-stabilizing auxiliaries in polyene cyclizations. 6. The fluorine atom as a cation-stabilizing auxiliary in biomimetic polyene cyclizations. 3. Use to effect regiospecific control

Author

William R. Bartlett, Rudolph K. Kullnig, Robert A. Buchanan, Fook S. Tham, and William S. Johnson

Subjects
Chemistry, medicine.medical_treatment, chemistry.chemical_element, General Chemistry, Halocarbon, Polyene, Biochemistry, Medicinal chemistry, Catalysis, Steroid, chemistry.chemical_compound, Colloid and Surface Chemistry, Fragmentation (mass spectrometry), Fluorine, medicine, Molecule, Aliphatic compound
Abstract

The fluorine atom substituted at the pro-C-13 position (steroid numbering) has been shown to be an effective cation-stabilizing (C-S) auxiliary in the acid-catalyzed cyclization of polyene substrates. The preparation of these polyenes employed the known fragmentation of cyclic epoxy hydrazones to construct the methylacetylenic and gem-dimethyl groups. The fluoroolefinic ketal Claisen and cyclopropylcarbinol rearrangements established the 3(E) and 11 (E) trisubstituted alkenes

Published
1993

8. Solid-state photochemistry. Remarkable effects of the packing of molecules in crystals on the diastereoselectivity of the intramolecular 2 + 2 photocycloaddition of a 4-(3'-butenyl)-2,5-cyclohexadien-1-one

Author

Rudolph K. Kullnig, Arthur G. Schultz, Fook S. Tham, Arthur G. Taveras, and Richard E. Taylor

Subjects
Colloid and Surface Chemistry, Intramolecular reaction, Chemistry, Intramolecular force, Solid-state, Molecule, Stereoselectivity, General Chemistry, Photochemistry, Biochemistry, Catalysis, Cycloaddition
Published
1992

13. Intramolecular 2 + 2 photocycloadditions of 4-(3'-alkenyl)- and 4-(3'-pentynyl)-2,5-cyclohexadien-1-ones

Author

Mark S. Plummer, Rudolph K. Kullnig, Arthur G. Taveras, and Arthur G. Schultz

Subjects
chemistry.chemical_classification, Intramolecular reaction, Chemistry, Carboxylic acid, Regioselectivity, General Chemistry, Photochemistry, Biochemistry, Catalysis, Cycloaddition, Colloid and Surface Chemistry, Intramolecular force, Photosensitizer, Triplet state, Solvent effects
Published
1988

14. The Structure of Cassaic Acid

Author

Rudolph K. Kullnig, Philip E. Shaw, Sol J. Daum, and Robert L. Clarke

Subjects
Crystallography, Colloid and Surface Chemistry, Chemistry, Structure (category theory), General Chemistry, Biochemistry, Catalysis
Published
1966

15. Incorporating CO into poly(alkoxymethylene)acyl ligands. Converting (Ph2PCH2CH2PPh2)(CO)2CoCOCH3 into threo-(DPPE)(CO)2CoCOCH(OEt)CH(OEt)CH3

Author

Chung C. Tso, Alan R. Cutler, and Rudolph K. Kullnig

Subjects
chemistry.chemical_classification, Chemistry, Ligand, Stereochemistry, Hydride, General Chemistry, Biochemistry, Catalysis, chemistry.chemical_compound, Colloid and Surface Chemistry, Electrophile, Selectivity, Carbonylation, Alkyl, Carbon monoxide, Group 2 organometallic chemistry
Abstract

Small organic molecules (C/sub 1/-C/sub 4/) can be prepared from carbon monoxide with transition organometallic complexes as templates. As a result of these studies, converting CO into poly(alkoxymethylene)acyl ligands that retain an oxygen functionality on each carbon center can be addressed. These acyl complexes could derive from repeating a three-step sequence of ligand reactions: (a) electrophilic activation of an acyl ligand, (b) hydride transfer to its oxycarbenoid derivative, and (c) carbonylation of the resulting alkoxyalkyl group. The first two steps, net reduction of the acyl ligand, are well established for alkyoxycarbene complexes (E = CH/sub 3/, CH/sub 2/CH/sub 3/). Carbonylating alkyl ligands bearing ..cap alpha..-alkoxy substituents (step c), however, is relatively difficult and only occurs in more labile organometallic systems. The authors now report coupling the acyl reduction (a and b) and carbonylation (c) steps by using the (dppe) (CO)/sub 2/Co system (dppe = Ph/sub 2/PCH/sub 2/CH/sub 2/PPh/sub 2/). These reactions moreover are stereoselective: complete diastereofacial selectivity at each emerging chiral center (step b) is observed in forming the cobalt diethoxybutanoyl.

Published
1987

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