Site-Selective Allylic and Propargylic C–H Amination

Site-Selective Allylic and Propargylic C–H Amination

Author: ChemistryViews

C–H functionalizations in allylic (or propargylic) positions give useful intermediates for further transformations in organic synthesis. In substrates with two different allylic protons, site selectivity can be a problem in such reactions. The effects of electron-withdrawing substituents can be used to increase the difference between the two C–H bonds and improve the site selectivity. However, the use of electron-donating groups in this context had not been reported so far.

Honggen Wang, Sun Yat-Sen University, Guangzhou, China, and colleagues have developed a boryl-directed intermolecular C–H amination of allyl N-methyliminodiacetyl boronates or propargylic N-methyliminodiacetyl boronates (B(MIDA)s) to give α-amino boronates with high site selectivity (general product structure pictured). In this approach, an electron-donating B(MIDA) group directs a selenium-catalyzed amination.

The team reacted a variety of primary and secondary allyl MIDA boronates with 2,2,2-trichloroethoxysulfonamide (TcesNH2) as an amino source, using 1,3-dimethyl-1,3-dihydro-2H-imidazole-2-selone as the catalyst, PhI(OAc)2 as an oxidant, and dichloromethane (DCM) as the solvent. Under slightly modified conditions, propargyl MIDA boronates were reacted with different sulfonamides, e.g., nitrobenzenesulfonamide (NsNH2), using PhI(OOCBn)2 as an oxidant.

The desired α-amino boronates were obtained in generally good to excellent yields and with high selectivities. The highly functionalized products are useful substrates for further reactions.


 

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