48 research outputs found
Synthesis of Highly Functionalized Bismacycles via Post-Transmetallation Modification of Arylboronic Acids
Bismacycles featuring a sulfone-bridged scaffold have recently been developed as versatile and convenient electrophilic arylating agents. Here, we report that the exocyclic aryl group, which is ultimately transferred to a nucleophilic coupling partner, can be functionalized through cross-coupling, heteroatom substitutions, oxidations and reductions, and protecting group manipulations. This “postsynthetic modification” approach provides concise and divergent access to complex aryl bismacycles. The utility of the functionalized bismacycles in electrophilic arylation of C–H and O–H bonds is demonstrated
Synthesis of Highly Functionalized Bismacycles via Post-Transmetallation Modification of Aryboronic Acids
Bismacycles featuring a sulfone-bridged scaffold have recently been developed as versatile and convenient electrophilic arylating agents. Here, we report that the exocyclic aryl group, which is ultimately transferred to a nucleophilic coupling partner, can be functionalized through cross-coupling, heteroatom substitutions, oxidations and reductions, and protecting group manipulations. This “postsynthetic modification” approach provides concise and divergent access to complex aryl bismacycles. The utility of the functionalized bismacycles in electrophilic arylation of C−H and O−H bonds is demonstrated
Interpreting ancient food practices:Stable isotope and molecular analyses of visible and absorbed residues from a year-long cooking experiment
Chemical analyses of carbonized and absorbed organic residues from archaeological ceramic cooking vessels can provide a unique window into the culinary cultures of ancient people, resource use, and environmental effects by identifying ingredients used in ancient meals. However, it remains uncertain whether recovered organic residues represent only the final foodstuffs prepared or are the accumulation of various cooking events within the same vessel. To assess this, we cooked seven mixtures of C3 and C4 foodstuffs in unglazed pots once per week for one year, then changed recipes between pots for the final cooking events. We conducted bulk stable-isotope analysis and lipid residue analysis on the charred food macro-remains, carbonized thin layer organic patina residues and absorbed lipids over the course of the experiment. Our results indicate that: (1) the composition of charred macro-remains represent the final foodstuffs cooked within vessels, (2) thin-layer patina residues represent a mixture of previous cooking events with bias towards the final product(s) cooked in the pot, and (3) absorbed lipid residues are developed over a number of cooking events and are replaced slowly over time, with little evidence of the final recipe ingredients
Enantioselective Synthesis of α‑Allyl-α-aryldihydrocoumarins and 3‑Isochromanones via Pd-Catalyzed Decarboxylative Asymmetric Allylic Alkylation
An
enantioselective Pd-catalyzed DAAA of α-aryl-β-oxo
esters has been developed employing the (<i>R,R</i>)-ANDEN-phenyl
Trost ligand to prepare a series of α-aryl-α-allyldihydrocoumarins
and 3-isochromanones. A variety of aryl groups were successfully employed
to afford the dihydrocoumarin and 3-isochromanone products in high
yields up to 95% and ee’s up to 96%. Under these conditions,
substrates containing di- and mono-<i>ortho</i>-substituted
aryl groups gave the highest levels of enantioselectivities. This
work represents the first example of the enantioselective preparation
of all-carbon quaternary α-allyl-α-aryl dihydrocoumarins
and 3-isochromanones
Enantiodivergent Synthesis of Tertiary α‑Aryl 1‑Indanones: Evidence Toward Disparate Mechanisms in the Palladium-Catalyzed Decarboxylative Asymmetric Protonation
Herein,
we describe a study into the scope and origin of an enantiodivergent
effect in the palladium-catalyzed decarboxylative asymmetric protonation.
By switching the achiral proton source, both enantiomers of a series
of tertiary α-aryl-1-indanones are readily accessed from the
corresponding α-aryl-β-keto allyl esters. In this example
of dual stereocontrol, enantioselectivities up to 94% (<i>S</i>) and 92% (<i>R</i>) were achieved using Meldrum’s
acid and formic acid, respectively. In an attempt to rationalize this
switch in absolute configuration an investigation of the ambiguous
mechanism of the decarboxylative asymmetric protonation was conducted.
A novel catalytic cycle for the reaction with formic acid is proposed
and subjected to a variety of experimental studies
Highly Enantioselective Construction of Sterically Hindered α‑Allyl-α-Aryl Lactones via Palladium-Catalyzed Decarboxylative Asymmetric Allylic Alkylation
Pd-catalyzed
decarboxylative asymmetric allylic alkylation has
been developed for sterically hindered α-aryl, β-oxo-allyl
ester lactone substrates. Pb-mediated α-arylation of the β-oxo-allyl
ester was used as the key step to synthesize the substrates for catalysis
in moderate to high yields. Optimization studies for decarboxylative
asymmetric allylic alkylations (DAAA) were conducted using δ-valerolactone-derived
α-aryl β-oxo-allyl ester with 2,4,6-trimethoxyphenyl as
the aryl substituent. Using (<i>R,R</i>)-ANDEN-phenyl Trost
as the chiral ligand, enantioselectivities of up to >99% ee and
98%
ee were achieved with the six-membered and five-membered lactone substrates,
respectively. Bulky aryl groups containing di-<i>ortho</i> substitutions and naphthyl groups gave the highest enantioselectivities.
This synthetic route allows for the simple modification of aryl groups,
giving highly enantioselective access to important structural motifs
Catalytic Asymmetric Synthesis of Sterically Hindered Tertiary α‑Aryl Ketones
The
catalytic asymmetric synthesis of a series of tertiary α-aryl
cyclopentanones and cyclohexanones has been accomplished via a Pd-catalyzed
decarboxylative protonation of the corresponding α-aryl-β-keto
allyl esters. Enantioselectivities of up to 92% <i>ee</i> and 74% <i>ee</i> were achieved for cyclopentanone and
cyclohexanone substrates, respectively. The route described gives
access to these important structural motifs in moderate to high levels
of enantioselectivity. In particular, this is only the second direct
approach for the preparation of tertiary α-aryl cyclopentanones.
The synthetic approach allows for simple modification of the aryl
group. Significantly, substrates containing sterically hindered aryl
groups gave the highest levels of enantioselectivity, and these aryl
groups were readily installed by a Pb-mediated arylation of a β-keto
allyl ester
Diastereofacial π‑Stacking as an Approach To Access an Axially Chiral P,N-Ligand for Asymmetric Catalysis
A phosphino-imidazoline (PHIM) ligand
possessing axial chirality
is prepared in a straightforward five-step synthesis. Configurational
stability around the chiral axis is achieved by the diastereofacial
π-stacking between the pentafluorophenyl and the naphthalene
rings. In particular, access to enantiopure ligand (<i>S,S,R</i><sub><i>a</i></sub>)-<b>2a</b> was realized by fractional
crystallization of the corresponding ∼3:1 atropdiastereomeric
mixture. The preliminary application of ligand (<i>S,S,R</i><sub><i>a</i></sub>)-UCD-PHIM showed excellent activities
in the enantioselective copper-catalyzed A3 coupling (ee’s
up to 98.1% and yields up to 98%)