Part I. An investigation into the mechanism of the samarium (II)-promoted Barbier reaction: Sequential radical cyclization/organometallic addition. Part II. Conjugate addition reactions of organosamarium reagents by in situ transmetalation to cuprates. Part III. Approximate absolute rate constants for the reaction of tributyltin radicals with aryl and vinyl halides. Part IV. An investigation into the synthetic utility of tri-n-butylgermanium hydride
An investigation of the mechanism of the samarium diiodide mediated Barbier reaction was conducted. Through a series of alkyl halide-carbonyl coupling and deuterium labelling experiments, evidence supportive of an organometallic addition mechanism was collected. Further probing led to an expansion of the utility of SmI[sub 2] in synthesis. The author has shown that radical cyclization of aryl and alkyl radicals to olefins, followed by reduction to primary and secondary organosamarium species is feasible. Organosamarium (III) reagents, produced by the reduction of alkyl and select aryl halides with 2 equiv of SmI[sub 2] in THF/HMPA, were treated with copper (I) salts and complexes to effect in situ transmetalation to cuprates. This allowed the 1,4-addition to [alpha],[beta]-unsaturated ketones. This new methodology allows for the sequential formation of carbon-carbon bonds through a combination of free radical and cuprate chemistry. Absolute rate constants for the abstraction of bromine atoms (k[sub Br]) by tri-n-butyltin radicals from a series of vinyl and aryl bromides have been determined. Atom abstraction was modestly enhanced by proximity of the halogen to a substituent in the following order: para < meta < ortho. Tri-n-butyl germanium hydride is known to be a poorer hydrogen atom donor than its tin analog. This feature makes it attractive for use in slow radical cyclizations where tin hydride would provide mainly for reduction. A brief study was executed to improve on the utility of the reagent as current conditions do not yield desired products in high amounts. Initial investigations examined the effect of initiator on reduction by germanium hydride, and subsequent experiments probed solvent effects. t-Butyl alcohol was determined to be superior to benzene or acetonitrile, giving consistently higher yields of reduction products.
- Research Organization:
- Pittsburgh Univ., PA (United States)
- OSTI ID:
- 5720032
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
ALKYL RADICALS
BROMIDES
BROMINE COMPOUNDS
BUTYL RADICALS
CHEMICAL REACTION KINETICS
CHEMICAL REACTION YIELD
CHEMICAL REACTIONS
COPPER COMPOUNDS
CUPRATES
CYCLIZATION
DEUTERIUM
GERMANIUM COMPOUNDS
GERMANIUM HYDRIDES
HALIDES
HALOGEN COMPOUNDS
HYDRIDES
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
IODIDES
IODINE COMPOUNDS
ISOTOPES
KETONES
KINETICS
LABELLING
LIGHT NUCLEI
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
RADICALS
RARE EARTH COMPOUNDS
REACTION KINETICS
REAGENTS
SAMARIUM COMPOUNDS
SAMARIUM IODIDES
STABLE ISOTOPES
TIN COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
YIELDS