Selective Ring-Opening of Nonactivated Amino Aziridines by Thiols and Unusual Nucleophilic Substitution of a Dibenzylamino Group

The reaction of chiral 2-(1-aminoalkyl)aziridines 1 with different thiols, in the presence of BF3·Et2O, is reported. The obtained products were dependent on the structure of the starting amino
aziridines 1. Thus, enantiopure (2S,3S)-2-(alkylthio)alkane-1,3-diamines 2 were obtained from
aziridines with C-2 substituents with lower steric congestion and partially racemized (2S,3S)-2,3-bis(alkylthio)alkan-1-amines 3 (ee = 56−66%) from aziridines with larger C-2 subtituents. In both
cases, the opening of the nonactivated aziridine ring at C-2 took place with retention of configuration
and proceeded with regio- and stereoselectivity at C-2. In the synthesis of 3, 2 equiv of thiol reacts
with 1 and the opening of aziridine ring at C-2 was followed by an unusual displacement of the
dibenzylamino group by a second equivalent of thiol. The regiochemistry and relative configuration
of compounds 3 was established by single-crystal X-ray analysis. A mechanism is proposed to explain
the results obtained.