Oxa-Michael-initiated cascade reactions of levoglucosenone

The reactions of aromatic aldehydes and levoglucosenone promoted by methoxide gives bridged α,β-unsaturated ketones, formed by a series of oxa-Michael-initiated cascade reactions in yields of up to 91% (14 examples). A complex series of equilibria operate during the reaction, and the formation of the bridged species is thermodynamically favored, except in the case of 5-methylfurfural and pyrrole-2-carboxaldehyde. This is the first report detailing this type of aldol/Michael cascade involving oxa-Michael initiation

Validation practices for satellite based earth observation data across communities

Assessing the inherent uncertainties in satellite data products is a challenging task. Different technical approaches have been developed in the Earth Observation (EO) communities to address the validation problem which results in a large variety of methods as well as terminology. This paper reviews state-of-the-art methods of satellite validation and documents their similarities and differences. First the overall validation objectives and terminologies are specified, followed by a generic mathematical formulation of the validation problem. Metrics currently used as well as more advanced EO validation approaches are introduced thereafter. An outlook on the applicability and requirements of current EO validation approaches and targets is given

Synthesis of a Chiral Auxiliary Family from Levoglucosenone and Evaluation in the Diels–Alder Reaction

A new family of chiral auxiliaries has been developed based on the lignocellulosic biomass pyrolysis product levoglucosenone. A promising single stereoisomer with an alcohol and π-stacking phenyl substituents was prepared in excellent yield in two steps from di­hydrolevoglucosenone without chromatography on >50 g scale. Acrylate esters prepared from the auxiliaries underwent diastereoselective Lewis acid promoted Diels–Alder reactions with cyclopentadiene (­endo/exo 98:2, endo d.r. up to 98:2), dimethylbutadiene (d.r. 93:7), and isoprene (d.r. > 98:2

Diastereoselective sulfa-Michael reactions controlled by a biomass-derived chiral auxiliary

A family of chiral auxiliaries derived from the lignocellulosic biomass pyrolysis product levoglucosenone (LGO) has been screened in the sulfa-Michael reaction. When promoted by inorganic bases with potassium counterions, the auxiliary with geminal benzyl substituents showed diastereoselectivity up to 90:10 for a broad range of α,β-unsaturated esters

The Iridoid Myodesert-1-ene and Elemol/Eudesmol are found in Distinct Chemotypes of the Australian Aboriginal Medicinal Plant 'Eremophila dalyana' (Scrophulariaceae)

The strongly aromatic Australian desert species 'Eremophila dalyana' is an Aboriginal medicinal plant that continues to be used today in Central Australia in the treatment of respiratory complaints and 'Sarcoptes scabiei' infestation. Using hydrodistillation of aerial parts of the plant, the new natural product myodesert-1- ene was isolated in two disjunct populations at up to 98% of the volatiles present in the hydrodistilled oils. Weak antimicrobial activities were observed for whole oils and myodesert-1-ene. Activities in the hydrodistilled oil were attributed to the antimicrobial sesquiterpenes elemol and eudesmol which showed good activity when isolated and were relatively abundant in the chemotype used medicinally. The biogenesis of myodesert-1-ene from iridodial is proposed

Biomimetic Synthesis of Mitchellenes B-H from the Abundant Biological Precursor 14-Hydroxy-6,12-muuroloadien-15-oic Acid

A step-economic biomimetic synthesis of mitchellenes B-H found in Eremophila sturtii has been achieved. Starting from the putative muurolane biological precursor, redox isomerization of the allylic alcohol gave an epimeric mixture of aldehydes, which could be used as a handle for cyclization onto the C6 position, using Bu3SnH-mediated radical cyclization or NHC-catalyzed Stetter reaction. The NHC-mediated approach was superior as the epimeric mixture underwent a dynamic kinetic resolution during the reaction, and reduction of the mixture with NaBH4 selectively formed the mitchellene ring system in 56% yield for the three steps. In the campaign to obtain the acid-starting material, two new natural products, mitchellene H and a muurolane aldehyde, were isolated. Synthetic procedures to access this family of natural products will enable further studies on their biological properties

Revision of the Phytochemistry of <i>Eremophila sturtii</i> and <i>E. mitchellii</i>

<i>Eremophila sturtii</i> and <i>E. mitchellii</i> are found in the arid and temperate regions of Australia and, because of their similar appearances, are often confused. Previous phytochemical investigations have described mitchellene sesquiterpenes (<b>1</b>–<b>5</b>) reported from <i>E. mitchellii</i> but are here demonstrated to be from <i>E. sturtii</i>. A previous study that described serrulatic acids (<b>16</b> and <b>17</b>) from a species reported as <i>E. sturtii</i> actually used <i>E. mitchellii</i>. In addition, two new C-15 modified analogues, mitchellenes F (<b>14</b>) and G (<b>15</b>), were isolated from <i>E. sturtii</i>. The absolute configuration of <b>14</b> was determined with the first X-ray structure of a compound with the mitchellene skeleton

Revision of the Phytochemistry of <i>Eremophila sturtii</i> and <i>E. mitchellii</i>

<i>Eremophila sturtii</i> and <i>E. mitchellii</i> are found in the arid and temperate regions of Australia and, because of their similar appearances, are often confused. Previous phytochemical investigations have described mitchellene sesquiterpenes (<b>1</b>–<b>5</b>) reported from <i>E. mitchellii</i> but are here demonstrated to be from <i>E. sturtii</i>. A previous study that described serrulatic acids (<b>16</b> and <b>17</b>) from a species reported as <i>E. sturtii</i> actually used <i>E. mitchellii</i>. In addition, two new C-15 modified analogues, mitchellenes F (<b>14</b>) and G (<b>15</b>), were isolated from <i>E. sturtii</i>. The absolute configuration of <b>14</b> was determined with the first X-ray structure of a compound with the mitchellene skeleton