Ynamides, as versatile synthetic precursors, have attracted much attention from synthetic chemists and sparked the development of a number of methodologies for the construction of various structures. 1H-Pyrrolo[2,3-d]carbazole is a core scaffold of a series of monoterpene indole alkaloids found in Kopsia, Strychnos, and Aspidosperma, for example. In this study, 1H-pyrrolo[2,3-d]carbazole derivatives were synthesized by a Brønsted acid-catalyzed tandem cyclization starting from tryptamine-based ynamides. This strategy prevented Wagner-Meerwein rearrangement by instantaneous intramolecular nucleophilic trapping of the indoleninium to afford a tetracyclic indoline via an in situ-formed enol species induced by the formation of a more stable conjugate diene moiety. The functional group tolerances were investigated by using a series of readily available substrates. A plausible mechanism has been proposed based on the evidence of the capture of the hemiaminal intermediate. Lastly, a Büchi ketone, which is the pivotal intermediate in the synthesis of the indole alkaloid vindorosine, was synthesized by utilizing our newly developed methodology.
N-Fluorobenzenesulfonimide was identified for the first time as a unique Ag(i)-catalyst attenuator in the annulation of a tryptamine-derived ynesulfonamide to an azepino[4,5-b]indole.
A microwave-irradiated solvent-free pinacol rearrangement of hydrobenzoin substrates catalyzed by a combination of N-fluorobenzenesulfonimide and FeCl·6HO was developed. Its selectivity was first investigated by density functional theory (DFT) calculations. Then the functional group tolerance was examined by synthesizing a series of substrates designed based on the insight provided by the DFT calculations. The application of the methodology was demonstrated by the efficient one-pot synthesis of (±)-latifine and (±)-cherylline, both are 4-aryltetrahydroisoquinoline alkaloids isolated from Amaryllidacecae plants.
What is already known on this topic?The health risk caused by high-temperatures depends on the interaction between high temperature exposure and the sensitivity and adaptability of the affected populations.
What is added by this report?A comprehensive assessment model was established by principal component analysis using the data of 19 cities, 15 provincial-level administrative divisions and used to identify regional characteristics and major influencing factors of health vulnerability to extreme heat in China.
What are the implications for public health practice?The results of the health vulnerability assessment could effectively identify the regions highly vulnerable to extreme heat in China and provide scientific evidence for the development of adaptive measures and resource allocation plans.
The spiro[indoline‐3,3′‐pyrrolidin]‐2‐ones were synthesized via a silica gel and alumina‐mediated sequential transformation based on tryptamine‐derived ynesulfonamide substrates under neat conditions. The inherent tendency of C−C bond migration through Wagner‐Meerwein rearrangement in the synthesis of spirooxindole was prevented by water trapping to the spiroindoleninium intermediate. The functional group tolerances of the methodology were investigated using a variety of substrates. The detailed mechanism of the sequential transformation was probed by the isotope‐labeled experiments. This strategy was further applied in the formal syntheses of indole alkaloids coerulescine and horsfiline.magnified image
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