Lanthanides in organic synthesis
The use of samarium diiodide in the mild, selective generation of carbon-carbon bonds has been explored. Barbier-type cyclizations of omega-iodoalkyl cycloalkanones were demonstrated to proceed in excellent yield. Unlike alkali or alkaline earth-promoted Barbier cyclizations, samarium diiodide was found to be effective for six-membered ring formation. Reaction conditions were also shown to be mild enough to tolerate remote functionality. Acyclic 2-(omega-iodoalkyl) ..beta..-ketoamides and 2-(3-iodopropyl) ..beta..-ketoesters were found to cyclize with high diastereoselectivity. The sense of selectivity was shown to be consistent with intramolecular chelation-controlled addition. The ..beta..-ketoamide substrates appear to undergo kinetic cyclization. However, ..beta..-ketoester substrates were found to equilibrate after cyclization via a retroaldol-aldol sequence. Acyclic 2-(3-iodopropyl) alkanones were cyclized in order to explore the stereoselectivity of intramolecular carbonyl addition, and relate this process to various transition state models for nucleophilic carbonyl addition. Samarium (II) carbenoids, generated from zero valent metal and geminal diiodides, were demonstrated to cyclopropanate allylic alcohols under exceptionally mild conditions in high yields. Samarium diiodide-promoted intramolecular Reformatsky-type cyclization of ..beta..-oxobromoacetates was shown to result in unprecedented 1,3-asymmetric induction. This methodology was found to be highly general with regard to the type of carbonyl substrate employed.
- Research Organization:
- Colorado Univ., Boulder (USA)
- OSTI ID:
- 7143658
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
ALCOHOLS
CATALYSIS
CATALYTIC EFFECTS
CHEMICAL REACTIONS
DEHYDROCYCLIZATION
HALIDES
HALOGEN COMPOUNDS
HYDROXY COMPOUNDS
IODIDES
IODINE COMPOUNDS
KETONES
ORGANIC COMPOUNDS
RARE EARTH COMPOUNDS
SAMARIUM COMPOUNDS
SAMARIUM IODIDES