Divergent Total Syntheses of Phragmalin and Khayanolide-Type Limonoids: A Torquoselective Interrupted Nazarov Approach.

The asymmetric and divergent total syntheses of two phragmalin (moluccensins G and H) and two khayanolide-type (krishnolide F and khayseneganin F) limonoids were disclosed, which employed a torquoselective interrupted Nazarov cyclization as the key step. Taken together with a Liebeskind-Srogl coupling, a benzoin condensation, and bidirectional acyloin rearrangements, our strategy would simplify the synthetic design of both phragmalin and khayanolide-type limonoids and facilitate their modular syntheses. Moreover, the described approach also provides additional insights into the biosynthetic relationships between these two distinct skeletons.

Total Synthesis of (-)-Retigeranic Acid A: A Reductive Skeletal Rearrangement Strategy.

The asymmetric total synthesis of (-)-retigeranic acid A was described, which relies on a crucial reductive skeletal rearrangement cascade for the controllable assembly of diverse angular triquinane subunits. Taken together with an intramolecular Michael/aldol cyclization, an ODI-[5 + 2] cycloaddition/pinacol rearrangement cascade, a Wolff ring contraction and a stereoselective HAT reduction, our synthetic approach has enabled the access to (-)-retigeranic acid A in a concise and practical manner.

Divergent Synthetic Approach to Grayanane Diterpenoids.

The total syntheses of nine grayanane diterpenoids, namely, GTX-II (), GTX-III (), rhodojaponin III (), GTX-XV (), principinol D (), iso-GTX-II (), 1,5-seco-GTX-Δ-ene (7), and leucothols B () and D (), that belong to five distinct subtypes, were disclosed in a divergent manner. Among them, six members were accomplished for the first time. The concise synthetic approach features three key transformations: (1) an oxidative dearomatization-induced [5 + 2] cycloaddition/pinacol rearrangement cascade to assemble the bicyclo[3.

Low-threshold ultraviolet stimulated emissions from large-sized single crystalline ZnO transferable membranes.

Wide-bandgap inorganic semiconductors based ultraviolet lasers bring versatile applications with significant advantages including low-power consumption, high-power output, robustness and long-term operation stability. However, flexible membrane lasers remain challenging predominantly due to the need for a lattice matched supporting substrate. Here, we develop a simple laser liftoff process to make freestanding single crystalline ZnO membranes that demonstrate low-threshold ultraviolet stimulated emissions together with large sized dimension (> 2 mm), ultralow-weight (m/A<15 g/m) and excellent flexibility.