Organolanthanide-catalyzed intramolecular hydroamination/cyclization/bicyclization of sterically encumbered substrates. Scope, selectivity, and catalyst thermal stability for amine-tethered unactivated 1,2-disubstituted alkenes

This paper reports the organolanthanide-catalyzed intramolecular hydroamination/cyclization of amine-tethered unactivated 1,2-disubstituted alkenes to afford the corresponding mono- and disubstituted pyrrolidines and piperidines using coordinatively unsaturated complexes of the type (eta(5)-Me5C5)(2)LnCH(TMS)(2) (Ln = La, Sm), [Me2Si(eta(5)-Me4C5)(2)]SmCH(TMS)(2), and [Me2Si(eta(5)-Me4C5)((BuN)-Bu-t)]LnE(TMS)(2) (Ln = Sm, Y, Yb, Lu; E = N, CH) as precatalysts. [Me2Si(eta(5)-Me4C5)((BuN)-Bu-t)]LnE(TMS)(2) mediates intramolecular hydroamination/cyclization of sterically demanding amino-olefins to afford disubstituted pyrrolidines in high diastereoselectivity (trans/cis = 16/1) and good to excellent yield. In addition, chiral C-1-symmetric organolanthanide catalysts of the type [Me2Si(OHF)(CPR*)]LnN(TMS)(2) (OHF = eta(5)-octahydrofluorenyl; Cp = eta(5)-C5H3; R* = (-)-menthyl; Ln = Sm, Y), and [Me2Si(eta(5)-Me4C5)(CpR*)]SmN(TMS)(2) (CP = eta(5)-H3C5; R* = (-)-menthyl) mediate asymmetric intramolecular hydroamination/cyclization of amines bearing internal olefins and afford chiral 2-substituted piperidine and pyrrolidine in enantioselectivities as high as 84:16 er at 60degreesC. The substrate of the structure NH2CH2CMe2CH2CH = CH(CH2)(2)CH = CH2 is regiospecifically bicyclized by [Me2Si(eta(5)-Me4C5)((BuN)-Bu-t)]LnE(TMS)(2) to the corresponding indolizidine skeleton in good yield and high diastereoselectivity. Thermolysis of (eta(5)-Me5C5)(2)LaCH(TMS)(2) in cyclohexane-d(12) at 120degreesC rapidly releases CH2(SiMe3)(2) and leads to possible formation of fulvene (eta(6)-Me4C5CH2-) species. The thermolysis product readily reverts to active catalysts upon protonolysis by substrate and exhibits the same catalytic activity as the (eta(5),eta(1)-Me5C5)(2)LaCH(TMS)(2) precatalyst at 120degreesC in the cyclization of cis- 2,2-dimethylhept-5-enylamine. Catalytically-active lanthanide-amido complexes (eta(5)-Me5C5)(2)La(NHR)(NH2R)(n) and [Me2Si(eta(5)-Me4C5)((BuN)-Bu-t)]Sm(NHR)(NH2R)(n) are shown to be thermally robust species.