A novel palladium-catalyzed decarboxylative coupling reaction of vinyl benzoxazinanones with arynes which may feature an intramolecular nucleophilic attack of an amino group at the central carbon of π-allylpalladium intermediate has been developed. The cis-5,5a,6,10b-tetrahydroindeno[2,1-b]indoles were generated in moderate to good yields. One key to the success of the present reaction was to achieve comparable rates for the palladium-catalyzed decarboxylation and aryne formation steps.
A novel and highly efficient synthetic approach to cyclopropanes was realized via 1,3-migration of acyloxy groups triggered by α-imino rhodium carbenes. Excellent chemoselectivity ensured broad compatibility of common functional groups. Merits such as readily available substrates, mild reaction conditions, and time-saving processes qualified this transformation as an attractive alternative strategy to synthesize multifunctionalized cyclopropanes. Primary investigations and discussion on the mechanism are presented.
Two reaction modes of pyridinium 1,4-zwitterionic thiolates with sulfenes generated in situ from alkanesulfonyl chlorides are described with DIPEA as the base. 3H-1,2-Dithiole 2,2-dioxides could be obtained via a formal [3 + 2] pathway from alkylmethanesulfonyl chlorides, while 1,9a-dihydropyrido[2,1-c]-[1,4]thiazines were obtained via a stepwise [(5 + 2) − 1] pathway from phenylmethanesulfonyl chlorides. Moreover, as an application, indolizines could be accessed via a stepwise {[(5 + 2) − 1] − 1} pathway, with 1,9a-dihydropyrido[2,1-c][1,4]thiazines as the transient intermediates.
Annulation of benzoxy‐tethered N‐sulfonyl‐1,2,3‐triazoles and indoles has been developed in this paper, providing an efficient and convenient access to valuable cyclopenta[b]indoles in moderate to good yields. α,β‐Unsaturated imine, which generated in situ from denitrogenation and 1,2‐OBz migration of triazole, provided three carbons for the formal [3+2] cyclization reaction for the first time.
The structurally complex alkaloid gelsemine was previously thought to have no significant biological activities, but a recent study has shown that it has potent and specific antinociception in chronic pain. While this molecule has attracted significant interests from the synthetic community, an efficient synthetic strategy is still the goal of many synthetic chemists. Here we report the asymmetric total synthesis of (+)-gelsemine, including a highly diastereoselective and enantioselective organocatalytic Diels–Alder reaction, an efficient intramolecular trans-annular aldol condensation furnishing the prolidine ring and establishing the configuration of the C20 quaternary carbon stereochemical centre. The entire gelsemine skeleton was constructed through a late-stage intramolecular SN2 substitution. The enantiomeric excess of this total synthesis is over 99%, and the overall yield is around 5%.
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