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