Abstract
A new efficient synthetic route to trans- 2,5-dihydro-1H-pyrroles and 1,2-dihydroquinolines that relies on copper(II) triflate-catalyzed intramo- lecular hydroamination of homoallylic amino alco- hols under mild and operationally straightforward conditions is described. For reactions leading to the trans-2,5-dihydro-1H-pyrrole product, yields of 52- 83% along with trans selectivities up to > 99:1 dr and ee values up to 97% were accomplished from enantioenriched 1-(tosylamino)pent-4-en-2-ols rang- ing from 91-99% ee. Without the need for inert and moisture-free conditions, reactions involving 1-(2- (tosylamino)phenyl)but-3-en-1-ols afforded the cor- responding 1,2-dihydroquinoline products in excel- lent yields up to 99% and with complete chemoselec- tivity. The mechanism is suggested to involve cop- per(II)-mediated dehydration of the homoallylic amino alcohol. Protonation of the resultant cop- per(II)-activated aminodiene is then thought to trig- ger subsequent intramolecular hydroamination to give the partially hydrogenated nitrogen heterocycle.
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