New methodology has been developed for the Lewis acid catalyzed synthesis of malonamides. First, the scandium(III)-catalyzed addition of diverse nucleophiles (e.g., indoles, N,N-dimethyl-m-anisidine, 2-ethylpyrrole, and 2-methylallylsilane) to coumarin-3-carboxylates has been developed to afford chromanone-3-carboxylates in high yields as a single diastereomer. Upon investigating a subsequent lanthanum(III)-catalyzed amidation reaction, a new multicomponent reaction was designed by bringing together coumarin-3-carboxylates with indoles and amines to afford indolylmalonamides, which were identified to exhibit fluorescent properties. The photophysical properties for selected compounds have been analyzed, including quantum yield, molar absorptivity, and Stokes shift. Synthetic studies of several reaction byproducts involved in the network of reaction equilibria for the three-component reaction provide mechanistic insight for the development of this methodology.
While
semisynthesis is a common platform for medicinal investigation
of steroidal systems, varying the nature of substitution and stereochemistry
at C9 and C10 remains challenging. It is demonstrated here that de
novo synthesis, enabled by a metallacycle-centered annulation reaction,
provides a uniquely effective means of addressing this problem. In
short, double asymmetric Friedel–Crafts cyclization proved
most effective for establishing anti- relative stereochemistry
(with respect to C13), while an intramolecular Heck reaction reliably
delivered the syn- diastereomers with high selectivity.
In addition, these studies reveal that this oxidative rearrangement
is effective for establishing a C10 quaternary center boasting variable
alkyl or aryl substitution.
The equivalent sand-grain roughness model is an empirical model initiated by Schlichting for predicting skin friction and heat transfer for turbulent flows over rough surfaces. For the equivalent sand-grain roughness model, rough surfaces with various features are compared to data from Nikuradse concerning flow in pipes with varying sizes of sieved sand glued to the wetted surface. Rough surfaces are assigned a value of equivalent sand-grain roughness height based on comparisons with Nikuradse’s fully rough data. Recent literature on the equivalent sand-grain roughness method has involved seeking correlations for equivalent sand-grain roughness height based on roughness metrics such as height, shape, and density. The Sigal-Danberg parameter has demonstrated the most promise for correlating the available equivalent roughness height data to geometric surface information. The Sigal-Danberg parameter was recently modified to include the mean surface elevation as an important parameter. While the modified Sigal-Danberg parameter provides a unified correlation for the equivalent sand-grain roughness height, the new formulation does not improve the scatter of the experimental data around the correlation. An uncertainty analysis is presented to evaluate the uncertainty of equivalent sand-grain roughness height predictions using the unified correlation. The analysis begins by estimating the uncertainties in the experimental measurements of Schlichting, and the uncertainty propagation is evaluated through each step of the equivalent sand-grain method development. The uncertainty associated with using empirical equations and conceptual uncertainties not associated with experimental measurements are also discussed. The result is an improved understanding of and uncertainty quantification for skin friction and heat transfer predictions made using equivalent sand-grain roughness methods.
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