Synthetic Studies toward Tubiferal A: Asymmetric Synthesis of a Model ABC-ring Compound

Synthetic studies on an ABC-ring model of Tubiferal A, a triterpenoid isolated from the fruit bodies of the Tubifera dimorphotheca myxomycete, are described. The stereogenic centers at the angular positions were constructed through the stereoselective addition of a C-ring allylborane followed by an Eschenmoser–Claisen rearrangement reaction prior to the formation of the AB-ring system by a double intramolecular alkylation reaction of a dichloro nitrile intermediate.

Synthesis of Tricyclic Marine Alkaloids, Cylindricines, Lepadiformines, Fasicularin, and Polycitorols: A Recent Update

Cylindricines, lepadiformines, and fasicularin are tricyclic marine alkaloids bearing perhydropyrrolo- and pyrido[2,1-j] frameworks having divergent chemical functionalities. They have been isolated from marine tunicates over the last two decades and found to have a range of cytotoxicity such as DNA-alkylating ability. Recently, polycitorols have emerged as a new member of this alkaloid family. Their unique structural features and biological activities have intrigued many researchers and challenged them in their synthesis. This review describes recent syntheses of the tricyclic alkaloids based on key synthetic approaches.1 Introduction2 Total and Formal Syntheses2.1 Overview of Synthetic Strategies2.2 Azaspirocycle (BC Ring) Approaches2.3 Indolizidine (AC Ring) Approaches2.4 Azadecalin (AB Ring) Approaches2.5 Tandem Cyclization Approaches3 Summary and Future Perspective

Synthesis of alkynyl-substituted camphor derivatives and their use in the preparation of paclitaxel-related compounds

Compounds containing two alkyne groups in close vicinity at the rigid skeleton of camphorsulfonamide show unique reactivities when treated with electrophiles or catalytic amounts of platinum(II). The formed product structures depend not only on the reagents used but also on the substituents attached to the triple bonds. Cycloisomerisations with perfect atom economy lead to polycyclic heterocycles that resemble to some extent the AB ring system of paclitaxel. Herein, we present practical synthetic methods for the selective synthesis of precursor dialkynes bearing different substituents (alkyl, aryl) at the triple bonds, based on ketals or an imine as protecting groups. We show for isomeric dialkynes that the reaction cascade induced by Pt(II) includes ring annulation, sulphur reduction, and ring enlargement. One isomeric dialkyne additionally allows for the isolation of a pentacyclic compound lacking the ring enlargement step, which we have proposed as a potential intermediate in the catalytic cycle.

A Derivation of Aharonov–Casher Phase and Another Adiabatic Approximation for Pure Gauge Under General Rashba Effects

Spin filters using spin–orbit interaction (SOI) are very important in the field of spintronics. Therefore, a theory of devices using SOI is necessary for designing the spin filters. The spin-filtering devices can be used to generate and detect spin polarized currents. Many researchers have reported on the spin-filters using linear Rashba SOI. However, the spin-filters using square and cubic Rashba SOIs are not yet reported. This is surely because the Aharonov–Casher (AC) phases acquired under square and cubic Rashba SOIs are ambiguous. In this paper, we try to derive the AC phases acquired under [Formula: see text]th order Rashba SOIs, which we call general Rashba SOIs, using non-Abelian SU (2) gauge theory. As a result, we have successfully derived these AC phases without completing the square methods which is useless except for linear Rashba SOI. In the process of derivation of AC phases, we have also found another expression of adiabatic approximation for a pure gauge. This finding will lead to the starting point for deeply understanding the adiabatic approximation. Using the above AC phases under general Rashba SOIs, we investigate the spin filter effect in Aharonov–Bohm (AB) ring with double quantum dots (QDs) under general Rashba SOIs. The spin transport is investigated from left nanowire to right nanowire in this structure within tight binding approximation. Especially, we focus on the difference of spin filter effects among general Rashba SOIs. We have obtained the penetrating magnetic flux dependence of spin polarization for the AB ring subject to general Rashba SOIs. It is found that the perfect spin filtering is achieved for all the Rashba SOIs. This result indicates that this AB ring under general Rashba SOIs can be a promising device for spin current generation without ferromagnetic metals. Moreover, this device under different order Rashba SOI behaves in totally different ways in response to penetrating magnetic flux, which is attributed to [Formula: see text] times rotation of directions of the effective magnetic field in the in-plane momentum. This fact means that we can determine the order of Rashba SOIs according to the peak position. We consider that this is very useful for many researchers.

Synthesis of the AB ring system of clifednamide utilizing Claisen rearrangement and Diels–Alder reaction as key steps

A synthesis to the functionalized AB ring system of clifednamide, member of macrocyclic tetramic acid lactams, was developed involving an Ireland–Claisen rearrangement and an intramolecular Diels–Alder reaction.