Synthetic And Mechanistic Features Of Base-catalyzed Homoenolization And Homoketonization

The behavior of a variety of homoenolate anions generated either by hydrolysis of polycyclic ethers (homoketonization) or by base-catalyzed hydrogen abstraction from polycyclic ketones (homoenolization) has been investigated.;A series of polycyclic derivatives of cyclopropanol were prepared and the base-catalyzed ketonization of the corresponding cyclopropoxides was examined to establish the regio- and stereochemistry of the ring cleavage. The examples derived from 2.2.1 and 2.2.2 ketones, by Simmons-Smith cyclopropanation of their silyl enol ethers, were found to undergo ring expansion preferentially while less-strained analogs gave the (alpha)-methyl derivatives of the initial ketone. In all cases of ring expansion, the cleavage proceeds with high stereoselectivity favoring inversion of configuration upon protonation (deuteration).;A novel means of generating the 2-trimethylsilyl ethers of substituted homoquadricyclenes was discovered. Base-catalyzed ketonization of these derivatives was found to yield either the tricyclo 3.2.1.0(\u272,7) or 3.3.0.0(\u272,8) octanone skeletons depending upon the substitution at the 8-position of the starting material.;The Simmons-Smith reaction with t-butyldimethylsilyl enol ether of some polycyclic ketones under concentrated conditions led to cyclopropanation and isomerization to furnish the ring expanded allylic silyl ethers.;The behavior of the 7,7-dimethyltricyclo 3.3.1.0(\u272,7) nonan-6-ones under strongly basic conditions was examined to determine the effect of the three-membered ring for comparison with earlier findings for the 3.2.1.0(\u272,4) analogs. While the endo isomer was found to be stable, the exo isomer readily rearranged to 8,8-dimethyltricyclo 4.3.0.0(\u272,4) nonan-7-one. Experiments in t-BuOD were carried out to establish the several sites of deuterium incorporation in the initial ketones. These results clearly revealed that the three membered ring influences both the regio- and stereochemistry of (beta)-enolate formation. The observed differences for the exo and endo isomers of the 3.3.1.0(\u272,4) nonanones can be attributed to conformational differences.;Some support for this proposal was provided by the reactivities of endo-9,9-dimethyltricyclo 5.3.1.0(\u272,6) undecan-8-one, endo-3-t-butyl-3-methylbicyclo 3.2.1 octan-2-one and endo-9-t-butyl-9-methyltricyclo 5.3.1.0(\u272,6) undecan-8-one under strongly basic conditions.;Homoenolization of the 3,3-dimethyl-7-spirocyclopropyl and -7-isopropylidene derivatives of norcamphor provide efficient syntheses of the corresponding 3,3-dimethyl-5-substituted norcamphors. Hydrogenolysis of the 5-spirocyclopropyl derivative furnished the hitherto unknown 3,3,5,5-tetramethylcamphor

Defining the opportunities, challenges, and research needs for nanobiomaterials derived from lignocellulosics

Issued as final reportNational Science Foundation (U.S

Cell wall response of field grown Populus to Septoria infection

Due to its ability to spread quickly and result in tree mortality, Sphaerulina musiva (Septoria) is one of the most severe diseases impacting Populus. Previous studies have identified that Septoria infection induces differential expression of phenylpropanoid biosynthesis genes. However, more extensive characterization of changes to lignin in response to Septoria infection is lacking. To study the changes of lignin due to Septoria infection, four field grown, naturally variant Populus trichocarpa exhibiting visible signs of Septoria infection were sampled at health, infected, and reaction zone regions for cell wall characterization. Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and acid hydrolysis were applied to identify changes to the cell wall, and especially lignin. FTIR and subsequent principal component analysis revealed that infected and reaction zone regions were similar and could be distinguished from the non-infected (healthy) region. NMR results indicated the general trend that infected region had a higher syringyl:guaiacyl ratio and lower p-hydroxybenzoate content than the healthy regions from the same genotype. Finally, Klason lignin content in the infected and/or reaction zone regions was shown to be higher than healthy region, which is consistent with previous observations of periderm development and metabolite profiling. These results provide insights on the response of Populus wood characteristics to Septoria infection, especially between healthy and infected region within the same genotype