Hiroya Kou

Copyright © 2020 American Chemical Society. Herein we report a one-step, catalytic, Markovnikov-selective, and scalable method for the synthesis of saturated sulfur heterocycles, which are found in the structures of pharmaceuticals and natural products, from an alkenyl thioester. Unlike a potentially labile alkenyl thiol, an alkenyl thioester is stable and easy to prepare. Powerful catalysis via a cobalt hydride hydrogen atom transfer and radical-polar crossover mechanism enabled simultaneous cyclization and deprotection. The substrate scope was expanded by extensive optimization of the reaction conditions and tuning of the thioester unit. This is a rare instance of thioesters showing nucleophilic behavior. This method was also applicable to alkenyl selenoesters.

Two different kind of sequential cyclization-functionalization are developed. Namely, cyclization-chlorination of 2-ethynylaniline derivatives using CuCl2 gave 3-chloro- and 3,5-dichloroindole derivatives. The plausible mechanism for this reaction is also discussed. On the other hand, the reaction between 2-ethynylaniline derivatives and Cu(NO3)(2)center dot 3H(2)O in THF provided C4-nitro compound. After being changed the solvent from THF to DMF, followed by heating, 5-nitroindole derivatives was afforded.

A mild, general, scalable, and functional group tolerant intramolecular hydroarylation of unactivated olefins using a Co(salen) complex, a N-fluoropyridinium salt, and a disiloxane reagent was reported. This method, which was carried out at room temperature, afforded six-membered benzocyclic compounds from mono-, 1,1- or trans-1,2-di, and trisubstituted olefins.

A mild, general, and functional group tolerant intramolecular hydroalkoxylation and hydroacyloxylation of unactivated olefins using a Co(salen) complex, an N-fluoropyridinium salt, and a disiloxane reagent is described. This reaction was carried out at room temperature and afforded five- and six-membered oxygen heterocyclic compounds, such as cyclic ethers and lactones. The Co complex was optimized for previously rare medium ring formation by hydrofunctionalization of unactivated olefins. The powerful Co catalyst system also enables the deprotective hydroalkoxylation of O-protected alkenyl alcohol and hydroacyloxylation of alkenyl ester to afford cyclic ethers and lactones directly. The substrate scope and mechanistic proof of deprotection were investigated. The experimental evidence supports the concerted transition state of the bond-forming step involving a cationic Co complex.

We developed an addition reaction of fluorous solvents to olefins using salen cobalt (Co) complex, N-fluoro-2,4,6-trimethylpyridinium tetrafluoroborate, and 1,1,3,3-tetramethyldisiloxane. This reaction condition was found to activate olefins, which enabled them to be attacked by 2,2,2-trifluoroethanol (TFE) and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), both of which are electronically weak nucleophiles.