5 research outputs found
Organocatalytic Stereoselective Synthesis of Acyclic γ‑Nitrothioesters with All-Carbon Quaternary Stereogenic Centers
A method
for the stereoselective synthesis of acyclic thioesters
bearing adjacent quaternary and tertiary stereogenic centers under
mild organocatalytic conditions was developed. α-Substituted
monothiomalonates (MTMs) were used as thioester enolate equivalents.
They reacted cleanly with nitroolefins in the presence of 1–6
mol % of cinchona alkaloid urea derivatives, and provided access to
γ-nitrothioesters with quaternary stereocenters in high yields
and diastereo- and enantioselectivities. Mechanistic investigations
provided insight into the parameters that determine the stereoselectivity
and showed that the diastereoselectivity can be controlled by the
nature of the MTM substrate. The different reactivities of the three
functional groups (oxoester, thioester, nitro moieties) within the
conjugate addition products allowed for straightforward access to
other compounds with quaternary stereogenic centers, such as γ-nitroaldehydes
and γ-butyrolactams
Organocatalytic Route to Dihydrocoumarins and Dihydroquinolinones in All Stereochemical Configurations
A straightforward
stereodivergent route to dihydrocoumarins and
dihydroquinolinones based on cinchona alkaloid catalyzed addition
reactions of monothiomalonates (MTMs) to functionalized nitroolefins
followed by deprotection and chemoselective cyclization has been developed.
The synthesis proceeds under mild conditions and yields heterocycles
with adjacent quaternary and tertiary stereogenic centers in very
high yields and stereoselectivities. Moreover, full control over the
relative and absolute configuration is achieved by the use of (pseudo)Âenantiomeric
catalysts and the difference in reactivity of thioester versus oxoester
moieties
Organocatalytic Route to Dihydrocoumarins and Dihydroquinolinones in All Stereochemical Configurations
A straightforward
stereodivergent route to dihydrocoumarins and
dihydroquinolinones based on cinchona alkaloid catalyzed addition
reactions of monothiomalonates (MTMs) to functionalized nitroolefins
followed by deprotection and chemoselective cyclization has been developed.
The synthesis proceeds under mild conditions and yields heterocycles
with adjacent quaternary and tertiary stereogenic centers in very
high yields and stereoselectivities. Moreover, full control over the
relative and absolute configuration is achieved by the use of (pseudo)Âenantiomeric
catalysts and the difference in reactivity of thioester versus oxoester
moieties
Diastereoselective Synthesis of CF<sub>3</sub>‑Substituted, Epoxide-Fused Heterocycles with β‑(Trifluoromethyl)vinylsulfonium Salts
CF<sub>3</sub>-substituted vinyl diphenylsulfonium triflate is an effective annulation reagent for the formation of α-CF<sub>3</sub> substituted, epoxide-fused heterocycles (pyrrolidines, piperidines, and tetrahydrofurans). This simple method affords a variety of valuable heterocyclic building blocks in a highly diastereoselective manner (dr >20:1)
Synthesis of α‑Substituted Vinylsulfonium Salts and Their Application as Annulation Reagents in the Formation of Epoxide- and Cyclopropane-Fused Heterocycles
The
discovery of new methods for the synthesis of classes of potentially
bioactive molecules remains an important goal for synthetic chemists.
Vinylsulfonium salts have been used for the synthesis of a wide variety
of small heterocyclic motifs; however, further developments to this
important class of reagents has been focused on reaction with new
substrates rather than development of new vinylsulfonium salts. We
herein report the synthesis of a range of α-substituted vinylsulfonium
tetraphenylborates (10 examples) in a 3 step procedure from commercially
available styrenes. The important role of the tetraphenylborate counterion
on the stability and accessibility of the vinylsulfonium salts is
also detailed. The α-substituted vinylsulfonium tetraphenylborates
gave good to excellent yields in the epoxyannulation of β-amino
ketones (15 examples) and the cyclopropanation of allylic amines (4
examples). Hydrogenation of an epoxyannulation product proceeded with
good diastereoselectivity