Rapid two-directional synthesis of the F-J fragment of the gambieric acids by iterative double ring-closing metathesis.
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Animals↗
Biomedical subjects
Marc C Kimber
Publications and source records attributed to Marc C Kimber.
Construction of building-blocks for polyether synthesis using sequential catalytic ring-closing enyne and cross metathesis.
Highly functionalised six- and seven-membered cyclic ethers bearing a variety of side chains have been synthesised using ring-closing enyne metathesis and subsequent cross metathesis of the intermediate diene; one-pot enyne and cross metathesis has also been accomplished, allowing ring construction and side chain introduction to be performed in a single operation.
Alkynes↗
A novel synthesis of functionalized tetrahydrofurans by an Oxa-Michael/Michael cyclization of gamma-hydroxyenones.
An approach to highly functionalized tetrahydrofuran derivatives based upon a novel Oxa-Michael/Michael dimerization of cis-gamma-hydroxyenones is presented. The reaction begins with either 1,2-dioxines or trans-gamma-hydroxyenones and proceeds by addition of one molecule of trans-gamma-hydroxyenone to another molecule of cis- or trans-gamma-hydroxyenone catalyzed by an alkoxide or hydroxide base. Subsequent intramolecular Michael addition of the keto-enolate gives the observed tetrahydrofurans. Substitution at both the 2- and 4-positions of the gamma-hydroxyenone is tolerated; however, for 4-substituted gamma-hydroxyenones, selectivity issues arise due to the possibility of heterochiral or homochiral dimerizations. The major products were those with all contiguous groups trans.
Journal Article↗
1,2-dioxines as masked cis gamma-hydroxy enones and their versatility in the synthesis of highly substituted gamma-lactones.
Addition of highly stabilized ester nucleophiles to 1,2-dioxines affords good to high yields of gamma-lactones with high diastereoselectivity. Heterolytic or homolytic cleavage of the 1,2-dioxines under appropriate conditions generates the key reactive cis gamma-hydroxy enones, which ultimately afford the observed gamma-lactones. Diastereoselectivity is installed as a result of anti 1,4-addition by the ester enolate to the cis enones followed by intramolecular cyclization. The reaction is tolerant of a range of substitution patterns on the 1,2-dioxine while a broad range of esters are also accommodated. In addition to the synthesis of racemic gamma-lactones, highly enantioenriched gamma-lactones can also be synthesized when chiral cobalt(II) catalysts are employed for the initial homolytic ring-opening of the 1,2-dioxine.
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An improved synthesis of cyclopropanes from stabilized phosphonates and 1,2-dioxines.
Addition of stabilized Horner-Wadsworth-Emmons (HWE) phosphonates to substituted 1,2-dioxines leads to diastereomerically pure di- and trisubstituted cyclopropanes in high yields and represents a viable alternative to ylides in the cyclopropanation reaction involving 1,2-dioxines. While yields are comparable, reaction times with these stabilized phosphonates were accelerated and the diastereoselectivity for this cyclopropanation reaction was significantly greater than for the previously reported examples employing ylides.
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First examples of the catalytic asymmetric ring-opening of meso 1,2-dioxines utilising cobalt(II) complexes with optically active tetradentate Schiff base ligands: formation of enantio-enriched cyclopropanes.
The combination of chiral cobalt beta-ketoiminato or cobalt salen complexes and meso 1,2-dioxines leads to catalytic asymmetric ring-opening affording enantio-enriched cis gamma-hydroxy enones; subsequent capture by an ylide affords enantio-enriched cyclopropanes.
Journal Article↗