Herein, we report ag eneral iminium ion-based catalytic method for the enantioselective conjugate addition of carbon-centered radicals to aliphatic and aromatic enals.T he process uses an organic photoredox catalyst, whicha bsorbs blue light to generate radicals from stable precursors,i n combination with ac hiral amine catalyst, which secures ac onsistently high level of stereoselectivity.T he generality of this catalytic platform is demonstrated by the stereoselective interception of aw ide variety of radicals,i ncluding nonstabilized primary ones whichare generally difficult to engage in asymmetric processes.T he system also served to develop organocatalytic cascade reactions that combine an iminiumion-based radical trap with an enamine-mediated step,affording stereochemically dense chiral products in one-step.
In this work, we exploit our strategy of in situ secondary-sphere modification of organocatalysts to improve the reactivity and selectivity of amino catalysts. Herein, the carboxylic acid moiety of proline...
The
chemical sciences are witnessing an influx of statistics into
the catalysis literature. These developments are propelled by modern
technological advancements that are leading to fast and reliable data
production, mining, and management. In organic chemistry, models encoded
with information-rich parameters have facilitated the formulation
of mechanistic hypotheses across different data-size regimes. Herein,
we aim to demonstrate through selected examples that the integration
of statistical principles into homogeneous catalysis can streamline
not only reaction optimization protocols but also mechanistic investigation
procedures. Namely, we highlight how different aspects of molecular
modeling, data set design, data visualization, and nuanced data restructuring
can contribute to improving chemical reactivity and selectivity, while
furthering our understanding of reaction mechanisms. By mapping out
these techniques at different data set sizes, we hope to encourage
the broad application of data-driven approaches for mechanistic studies
regardless of the accessible amount of data.
A new and facile one-pot synthesis of 1,3-disubstituted allenes, using cheap and readily available terminal alkynes, benzaldehyde derivatives and morpholine, was developed. A small library of 20 allenes demonstrates a broad applicability, with yields up to 86%. Isotopic-labelling and cross-over experiments strongly indicate that our reaction proceeds via a two-step A 3 -coupling followed by a 1,5-hydrogen shift process.
The critical influence of solvent
effects on proline-catalyzed
aldol reactions has been extensively described. Herein, we apply multivariate
regression strategies to probe the influence of different solvents
on an aldol reaction catalyzed by proline modified at its secondary
sphere with boronic acids. In this system, both
in situ
binding of the boronic acid to proline and the outcome of the aldol
reaction are impacted by the solvent-controlled microenvironment.
Thus, with the aim of uncovering mechanistic insight and an ancillary
aim of identifying methodological improvements, we designed a set
of experiments, spanning 15 boronic acids in five different solvents.
Based on hypothesized intermediates or interactions that could be
responsible for the selectivity in these reactions, we proposed several
structural configurations for the library of boronic acids. Subsequently,
we compared the statistical models correlating the outcome of the
reaction in different solvents with molecular descriptors produced
for each of these proposed configurations. The models allude to the
importance of different interactions in controlling selectivity in
each of the studied solvents. As a proof-of-concept for the practicality
of our approach, the models in chloroform ultimately led to lowering
the ketone loading to only two equivalents while retaining excellent
yield and enantio- and diastereo-selectivity.
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