A New Route to Diastereomerically Pure Cyclopropanes Utilizing Stabilized Phosphorus Ylides and γ-Hydroxy Enones Derived from 1,2-Dioxines: Mechanistic Investigations and Scope of Reaction
作者:Thomas D. Avery、Dennis K. Taylor、Edward R. T. Tiekink
DOI:10.1021/jo0002240
日期:2000.9.1
setting up the observed cis stereochemistry between H1 and H3. Cyclization of the resultant enolate (30a or 30b), expulsion of triphenylphosphine oxide, and proton transfer from the reaction manifold affords the observed cyclopropanes in excellent diastereomeric excess. The utilization of Co(SALEN)(2) in a catalytic manner also allows for a dramatic acceleration of reaction rates when entering the reaction
Osmium Catalyzed Dihydroxylation of 1,2-Dioxines: A New Entry for Stereoselective Sugar Synthesis
作者:Tony V. Robinson、Dennis K. Taylor、Edward R. T. Tiekink
DOI:10.1021/jo060949p
日期:2006.9.1
A series of 3,6-substituted 3,6-dihydro-1,2-dioxines were dihydroxylated with osmium tetroxide to furnish 1,2-dioxane-4,5-diols (peroxy diols) in yields ranging from 33% to 98% and with de values not less than 90%. The peroxy diols were then reduced to generate a stereospecific tetraol core with R, R, S, S or "allitol" stereochemistry. The peroxy diols and their acetonide derivatives were also ring-opened with Co(II) salen complexes to give novel hydroxy ketones in 77-100% yield, including the natural sugar psicose. Importantly, preliminary work on the catalytic asymmetric ring-opening of meso-peroxy diols using the Co(II) Jacobsens's catalyst indicates that asymmetric sugar synthesis from 1,2-dioxines is possible.
Chemistry of singlet oxygen. 51. Zwitterionic intermediates from 2,4-hexadienes