Journal article
Mn-mediated coupling of alkyl iodides and chiral N-acylhydrazones: optimization, scope, and evidence for a radical mechanism
Journal of organic chemistry, Vol.71(18), pp.7016-7027
09/01/2006
DOI: 10.1021/jo061158q
PMID: 16930057
Abstract
Stereoselective radical additions have excellent potential as mild, nonbasic carbon-carbon bond constructions for direct asymmetric amine synthesis. Efficient intermolecular radical addition to C=N bonds with acyclic stereocontrol has previously been limited mainly to secondary and tertiary radicals, a serious limitation from the perspective of synthetic applications. Here, we provide full details of the use of photolysis with manganese carbonyl to mediate stereoselective intermolecular radical addition to N-acylhydrazones. Photolysis (300 nm) of alkyl halides and hydrazones in the presence of Mn2(CO)10 and InCl(3) as a Lewis acid led to reductive radical addition; diastereomer ratios ranged from 93:7 to 98:2 at ca. 35 degrees C. The reaction tolerates additional functionality in either reactant, enabling subsequent transformations as shown in an efficient asymmetric synthesis of coniine. A series of hydrazones bearing different substituents on the oxazolidinone auxiliary were compared; consistently high diastereocontrol revealed that the identity of the substituent had little practical effect on the diastereoselectivity. Further mechanistic control experiments confirmed the intermediacy of radicals and showed that independently prepared alkyl- or acylmanganese pentacarbonyl compounds do not undergo efficient addition to the N-acylhydrazones under thermal or photolytic (300 nm) conditions. These Mn-mediated conditions avoid toxic tin reagents and enable stereoselective intermolecular radical additions to C=N bonds with the broadest range of alkyl halides yet reported, including previously ineffective primary alkyl halides.
Details
- Title: Subtitle
- Mn-mediated coupling of alkyl iodides and chiral N-acylhydrazones: optimization, scope, and evidence for a radical mechanism
- Creators
- Gregory K Friestad - Department of Chemistry, University of Iowa, Iowa City, IA 52242, USA. gregory-friestad@uiowa.eduJean-Charles MariéYoungSung SuhJun Qin
- Resource Type
- Journal article
- Publication Details
- Journal of organic chemistry, Vol.71(18), pp.7016-7027
- DOI
- 10.1021/jo061158q
- PMID
- 16930057
- NLM abbreviation
- J Org Chem
- ISSN
- 0022-3263
- eISSN
- 1520-6904
- Publisher
- United States
- Language
- English
- Date published
- 09/01/2006
- Academic Unit
- Chemistry
- Record Identifier
- 9983985718402771
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