18 research outputs found
Regioselective Cyclization of (Indol-3-yl)pentyn-3-ols as an Approach to (Tetrahydro)carbazoles
An acid-catalyzed,
highly regioselective cycloisomerization as
well as dehydro-cyclization of (indol-3-yl)pentyn-3-ols has been reported
for the selective synthesis of tetrahydrocarbazoles and carbazoles.
This process is mild and found to be very general in terms of structural
diversity of substrates. Utilizing the strategy, an efficient synthetic
approach for the functionalized frameworks of carbazomycins A–D
has also been developed
An Unprecedented (Semi)Favorskii Rearrangement. Evidence for the 2‑(Acyloxy)cyclopropanones
Discovery
and development of an unprecedented (semi)Favorskii rearrangement
has been reported. The intermediacy of structurally singular (acyloxy)cyclopropanones
has been unraveled by fruitful control experiments including a crossover
experiment. This class of cyclopropanones is found to be inert for
classical Favorskii functionalization and preferably undergoes a decycloisomerization
(ring–chain valence tautomerism) to α-(acyloxy)enones.
A cascade conversion of α,α-diiodo-α′-acetoxyketones
to (acyloxy)cyclopropanones via α-iodo-α′-acetoxyketones
has been achieved by the synchronous dual basicity (Lewis and Brønsted)
of amines. The overall process is found to be very general for diverse
substrates and highly efficient
Enantioselective total synthesis and assignment of the absolute configuration of (+)-laurokamurene B
The first enantioselective total synthesis of the rearranged aromatic sesquiterpene (+)-laurokamurene B, isolated from the Chinese red algae Laurencia okamurai Yamada, has been accomplished starting from (S)-campholenaldehyde, establishing the absolute configuration of laurokamurenes
Enantiospecific synthesis of the tricyclic core structure of lippifolianes
An enantiospecific synthesis of the [6.6.3]-tricyclic carbon framework, 2,6,6,9-tetra-methyltricyclo[5.4.0.02,4]undecane, present in the sesquiterpenes lippifolianes and the diterpenes cyclosclareol, metasequoic acids and parguerols, starting from the readily available monoterpene (R)-carvone, is described
Stereoselective, Cascade Synthesis of <i>trans</i>-Enynones through Coupling-Isomerization Reaction
A mild,
cascade methodology based on the modified Cadiot–Chodkiewicz
reaction was developed for the stereoselective synthesis of <i>trans</i>-enynones. By this methodology, structurally divergent <i>trans</i>-enynones, which are embedded with sensitive functional
groups, were synthesized. Control experiments suggested that the CuCl
alone does not have a role in the isomerization step, whereas the
CuCl–piperidine complex (formed during the cross coupling)
may have a rate enhancing effect. Furthermore, additional sets of
control experiments favor the involvement of unimolecular [1,2]-H
shift rather than a homobimolecular proton abstraction during the
isomerization step
Mild Approach to 2‑Acylfurans via Intercepted Meyer–Schuster Rearrangement of 6‑Hydroxyhex-2-en-4-ynals
We
have developed a mild, intramolecular intercepted Meyer–Schuster
(M-S) rearrangement for the synthesis of 2-acylfurans from corresponding <i>cis</i>-6-hydroxyhex-2-en-4-ynals. This reaction was found to
be very general, and the starting materials are easily accessible.
By this methodology the first synthesis of deoxy-<i>nor</i>-abiesesquine B, a sesquiterpene, was also achieved in three steps.
The concept of adding two nucleophiles during the M-S rearrangement
was introduced
Rates of Hexadehydro-Diels–Alder (HDDA) Cyclizations: Impact of the Linker Structure
The
rates of the hexadehydro-Diels–Alder (HDDA) reaction
of substrates containing, minimally, a 1,3,8-triyne subunit are reported.
Several series of related substrates, differing in the nature of the
three-atom tether that links the 1,3-diyne and diynophile, were examined.
Seemingly small changes in substrate structure result in large differences
in cyclization rate, spanning more than 8 orders of magnitude. The
reactivity trends revealed by these studies should prove useful in
guiding substrate design and choice of reaction conditions in future
applications
Mechanistic Duality in Tertiary Amine Additions to Thermally Generated Hexadehydro-Diels–Alder Benzynes
Reported here are
studies directed at understanding the mechanism
of tertiary amine addition to hexadehydro-Diels–Alder (HDDA)-generated
benzynes. Tertiary amines are presumed to engage benzynes by generation
of a zwitterionic intermediate. Simple trialkylamines undergo <i>inter</i>molecular protonation by a protic nucleophile to give
an aryl ammonium intermediate that is then dealkylated. Amines containing
acidified β-protons undergo an <i>intra</i>molecular
elimination to give the aniline and an alkene. Finally, amino alcohols
react at either of their N- or O atoms, depending upon the extent
of internal hydrogen bonding