67 research outputs found
Regio- and Stereoselective Cyanotriflation of Alkynes Using Aryl(cyano)iodonium Triflates
A novel, mild, and versatile approach
for regioselective <i>syn</i>-addition of both the CN and
OTf groups of arylÂ(cyano)Âiodonium
triflates to alkynes is described. The reaction uses Fe-catalysis
and can be conducted in gram scale. Products of the vicinal cyanotriflation
can be stereospecifically readily further functionalized, rendering
the method highly valuable
2‑Trifluoromethylated Indoles via Radical Trifluoromethylation of Isonitriles
Either
two or three C–C bonds are formed in the synthesis
of 2-trifluoromethylindoles starting with readily prepared isonitriles
and the Togni reagent as CF<sub>3</sub> radical precursor. These transformations
occur in the absence of transition metal, and products are obtained
in moderate to good yields with excellent diastereoselectivity
Sodium-Ketyl Radical Anions by Reverse Pinacol Reaction and Their Coupling with Iodoarenes
Transition-metal-free
C–C bond formation between aryl iodides
and pinacols is presented. Pinacols are readily transformed by deprotonation
with NaH to their Na-pinacolates. C–C-bond homolysis at room
temperature generates in situ the corresponding Na-ketyl radical anions
which react with various aryl iodides in a homolytic aromatic substitution
reaction to form tertiary Na-alcoholates. Protonation eventually provides
tertiary alcohols in an unprecedented route
Perfluoroalkylation of Aryl‑<i>N</i>,<i>N</i>‑dimethyl Hydrazones Using Hypervalent Iodine(III) Reagents or Perfluoroalkyl Iodides
Radical trifluoromethylation of aryl <i>N</i>,<i>N</i>-dimethyl hydrazones using TBAI as an
initiator and Togni’s
reagent as a trifluoromethyl radical source is described. Cascades
proceed via electron-catalysis; this approach is generally more applicable
to hydrazone perfluoroalkylation using perfluoroalkyl iodides as the
radical precursors in combination with a base under visible-light
initiation
1‑Trifluoromethylisoquinolines from α‑Benzylated Tosylmethyl Isocyanide Derivatives in a Modular Approach
The preparation of various 1-trifluoromethylisoquinolines
from
α-benzylated tosylmethyl isocyanide derivatives and the commercial
Togni reagent using a radical cascade is reported. The starting isocyanides
are readily prepared in a modular sequence from commercial tosylmethyl
isocyanide via sequential double α-alkylation, and the radical
reaction proceeds under mild conditions with high efficiency without
any transition-metal catalyst via electron catalysis. This valuable
protocol has been successfully applied to the total synthesis of CF<sub>3</sub>-mansouramycin B
Reaction of Arynes with Vinyl Sulfoxides: Highly Stereospecific Synthesis of <i>ortho</i>-Sulfinylaryl Vinyl Ethers
The
reaction of in situ generated arynes with aryl vinyl sulfoxides
provides <i>ortho</i>-arylsulfinylaryl vinyl ethers via
aryne σ-bond insertion into the S–O-bond and concomitant
stereospecific S–O-vinyl migration. The cascade allows preparing
di- or trisubstituted vinyl ethers with excellent stereospecificity.
The reactions proceed under mild conditions, the substrate scope is
broad, and the products obtained are valuable
Copper-Catalyzed Intermolecular Aminoazidation of Alkenes
Copper-catalyzed
intermolecular aminoazidation of alkenes is described.
This novel methodology provides an efficient approach to vicinal amino
azides which can easily be transformed into other valuable amine derivatives.
The commercially available <i>N</i>-fluorobenzenesulfonimide
(NFSI) is used as a nitrogen-radical precursor and TMSN<sub>3</sub> as the N<sub>3</sub> source. Yields are moderate to excellent, and
for internal alkenes aminoazidation occurs with excellent diastereoselectivity
Stereoselective Radical Azidooxygenation of Alkenes
Radical azidooxygenation of various alkenes is described. A readily prepared N<sub>3</sub>-iodine(III) reagent acts as a clean N<sub>3</sub>-radical precursor. Radical generation is achieved with TEMPONa acting as a mild organic reducing reagent. The C-radical generated after N<sub>3</sub>-radical addition is efficiently trapped by <i>in situ</i> generated TEMPO. Yields are good to excellent, and for cyclic systems azidooxygenation occurs with excellent diastereoselectivity
9‑Silafluorenes via Base-Promoted Homolytic Aromatic Substitution (BHAS) – The Electron as a Catalyst
Transition-metal-free
intramolecular radical silylation of 2-diphenylÂsilylbiaryls
via base-promoted homolytic aromatic substitution (BHAS) to give 9-silafluorenes
is reported. 2-DiphenylÂsilylbiaryls are readily prepared, and
cross dehydrogenative silylation occurs with <i>tert</i>-butylhydroÂperoxide (TBHP) as a cheap stoichiometric oxidant
in the presence of a small amount of tetraÂbutylÂammonium
iodide (TBAI) as an initiator. These cyclizations are catalyzed by
the electron
Short and Protecting-Group-Free Approach to the (−)‑Δ<sup>8</sup>‑THC-Motif: Synthesis of THC-Analogues, (−)-Machaeriol B and (−)-Machaeriol D
Friedel–Crafts
alkylation of resorcinols with (<i>S</i>)-<i>cis</i>-verbenol and subsequent cyclization allows
the construction of the tetrahydroÂdibenzopyran core of (−)-Δ<sup>8</sup>-THC which is also found in other natural products in one
step. Using a benzofuryl substituted resorcinol, followed by diastereoselective
hydroboration and oxidative or reductive workup, directly provides
(−)-machaeriol B and D in 42% and 43% overall yields. Bromoresorcinol
as a coupling partner delivers Br–THC that can be applied for
late-stage diversification by Suzuki–Miyaura cross-coupling
to readily access (−)-Δ<sup>8</sup>-THC analogues
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