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Dissertation Information for Christopher Sean Straub

NAME:
- Christopher Sean Straub

DEGREE:
- Ph.D.

DISCIPLINE:
- Chemistry

SCHOOL:
- Emory University (USA) (2000)

ADVISORS:
- Albert Padwa

COMMITTEE MEMBERS:
- Frank E. McDonald
- Lanny S. Liebeskind

MPACT Status: Fully Complete

Title: Rhodium-mediated cyclizations of alpha-diazo carbonyl compounds: The use of diazo imides and acetylenic diazo esters for alkaloid synthesis

Abstract: "Rhodium(II) catalyzed decomposition of ¦Á-diazo esters containing alkynyl tethers results in the formation of vinyl carbenoids which can be intercepted by adjacent carbonyl groups to produce 2-heteroatom substituted furans. This tandem cyclization/6¦Ð-electrocyclization sequence is dependent on many factors, including the solvent employed, the ligands attached to the rhodium catalyst, the conformational rigidity of the system, and the substituents on the alkynyl tether. When terminal alkynes are used the cyclization does not occur. However, the presence of a trimethylsilyl group at the terminal position facilitates the reaction and permits access to various 2-alkoxy and 2-amino substituted furans. The intermolecular Diels-Alder cycloaddition of these furans was explored. By varying the conditions and the dienophiles used it was possible to produce an array of heterocyclic compounds. Protodesilylation of the silyl substituted furans prior to the Diels-Alder reaction greatly facilitated the cycloaddition. This protocol was also employed for the synthesis of furans containing tethered ¦Ð-bonds. Protodesilylation of these furan systems followed by thermolysis produced novel polycyclic ring systems. Several model systems were examined with the intention of using the methodology towards a planned synthesis of the alkaloid strychnine.

Rhodium carbenoids were also found to cyclize onto adjacent imide carbonyls to form reactive mesoionic compounds known as isom¨¹nchnones. These reactive dipoles react with various dipolarophiles to form oxabicyclic compounds that can be employed for the synthesis of a wide variety of natural products. When a sulfonyl group is attached to the diazoimide skeleton, 3-hydroxy-2-pyridones were efficiently produced. Substituents on the pyridone ring were introduced by varying both the diazo precursor and the dipolarophile. Conversion of the hydroxyl group on the ring into the corresponding triflate allows for the introduction of various substituents via a palladium-catalyzed cross-coupling reaction. This protocol had been used for the synthesis of two structurally simple alkaloids, coniceine and (¡À)-ipalbidine. The methodology was also applied to the synthesis of (¡À)-septicine and the angiotensin converting enzyme inhibitor A58365A. These syntheses underscore the flexibility of the [3+2]-cycloaddition reaction of phenylsulfonyl substituted isom¨¹nchnones."

MPACT Scores for Christopher Sean Straub

A = 0
C = 0
A+C = 0
T = 0
G = 0
W = 0
TD = 0
TA = 0
calculated 2008-04-13 14:01:43

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