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Dissertation
A study of two modified hydride delivery systems
Doctor of Philosophy (Ph.D.), Drexel University
1983
DOI:
https://doi.org/10.17918/00008024
Abstract
Part I. The reductive displacements by hydride transfer reagents of a number of allylic leaving groups (e.g., esters, ethers, tosylates, halides, alcohols, silyl ethers, phenyl sulfones, phenyl sulfides, phenyl selenides) to form alkenes via catalytic activation by tetrakis(triphenylphosphine)palladium (O) was investigated. Substantial control in determining the position of the double bond in product alkenes was found to be possible through proper selection of the hydride reagent. From primary allylic substrates, ammonium formate and formic acid hydride transfer agents afforded predominantly 1-alkenes. In contrast, LiEt(,3)BH and i-Bu(,2)AlH gave 2-alkenes almost exclusively and with a high degree of maintenance in the stereo-chemical integrity of the double bond. Weaker hydride sources (e.g., NaBH(,3)CN, NaBH(,4)) exhibited inferior regio- and stereoselectivity. A mechanistic rationale for the differing selectivities is given. These results establish a useful synthetic method in terms of the conversion of substrates containing allylic functionalities into alkenes. They also present a useful means of protecting -OH, -SO(,2)H, -SH, and -SeH functionalities via formation of allyl derivatives and subsequent deprotection with Pd(O)/hydride reduction. In the absence of a hydride reagent, in dimethylsulfoxide solvent, allylic substrates undergo a palladium catalyzed-elimination reaction affording conjugated dienes in good yield. Part II. The reducing ability of sodium dimethylaminotrihydroborate (1-) (NaDMAB) towards a number of common organic functional groups was investigated. Aldehydes, ketones, and esters were reduced to the corresponding alcohols in high yield. Primary amides were reduced to the corresponding amines. Tertiary amides were reduced to alcohols (e.g., N,N-dimethylamides) or amines (e.g., N,N-diisopropylamides) depending on the bulk of the alkyl substituents on nitrogen. Secondary amides were not reduced by NaDMAB. As a result, primary and tertiary amides can be selectively reduced in the presence of secondary amides. A mechanistic rationale is given. Whereas aryl halides were reduced to arenes, alkyl halides and an epoxide were attacked by the dimethylamine portion of NaDMAB affording the corresponding amines. Nitriles were also reduced to amines. The reductions of a nitro compound and a sulfoxide afforded pre-dominantly axo compounds and cleavage products, respectively.
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Details
- Title
- A study of two modified hydride delivery systems
- Creators
- Keith S. Learn
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xii, 316 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- College of Science (1970-1990); Drexel University
- Other Identifier
- 991021888827704721