Further studies of the direct enantioselective α-hydroxymethylation of aldehydes employing the α,α-diarylprolinol trimethylsilyl ether class of organocatalysts are described. This process has proven efficient for access to β-hydroxycarboxylic acids and δ-hydroxy-α,β-unsaturated esters from aldehydes in generally good yields, excellent enantioselectivity, and compatibility with a broad range of functional groups in the aldehyde. The goal of these studies was to identify the critical reaction variables that influence the yield and enantioselectivity of the α-hydroxymethylation process such as catalyst structure, pH of the medium, purity of the reactants and reagents particularly with respect to the presence of acidic impurities, and the nature of the buffer, along with the standard variables including solvent, time, temperature and mixing efficiency. The previously identified intermediate lactol has been further characterized and its reactivity examined. These studies have led to identification of the most critical variables translating directly into improved substrate scope, reproducibility, enantioselectivity, and yields.
Reformed Experimental Activities
(REActivities) is an innovative
approach to the delivery of the traditional material in an undergraduate
organic chemistry laboratory. To better understand the fidelity of
implementing this pedagogy and what effects the framework of REActivities
has on student–instructor interactions, an observational protocol
study was employed. This paper also describes the Evaluation of Lab
Instructor Time and Engagement (ELITE) observational instrument developed
to evaluate instructional behaviors in a lab setting. The instrument
was used in first semester undergraduate organic chemistry laboratories
across seven universities to measure the robustness of the guided-inquiry
materials when implemented and the nature of the instructor’s
interactions. The ELITE data was analyzed for laboratories delivered
using REActivities and compared with expert delivery as well as with
traditional expository methods. The data revealed that instructor
behaviors when using REActivities were consistent and comparable and
could be distinguished from traditional lab deliveries. The nature
of the instructor’s behaviors also showed a remarkably consistent
trend for coded conceptual-based discussion when REActivities was
employed, in contrast to the near absence of similar interactions
when expository methods were employed for comparable laboratories.
(
S
)‐1,1‐Diphenylprolinol trimethylsilyl ether is readily prepared by the silylation of (
S
)‐1,1 diphenylprolinol. Commercial sources of diphenylprolinol can be expensive, and current methods for the synthesis of diphenylprolinol and its derivatives are low yielding, practically challenging on scale, or include hazardous reagents such as phosgene. The method reported provides access to diphenylprolinol in two steps from the Boc‐protected methyl ester of proline, and the trimethylsilylether of diphenylprolinol via a single transformation from diphenyl prolinol.
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