RESUMEN
Organocatalytic asymmetric desymmetrization of prochiral cyclohexane-1,3-diones has been demonstrated through the merging of iminium and enamine activation. The tandem annulation reaction proceeds through a sequential oxa-Michael addition/intramolecular aldol reaction/[1,3]-amino oxetane rearrangement pathway. Mechanistic study using an 18O-water experiment suggests oxetane rearrangement instead of direct dehydration. The formation of other competing Rauhut-Currier products via alkoxy-elimination was not observed.
RESUMEN
In this work, we have developed an unconventional and highly enantioselective solvent-promoted Rauhut-Currier cyclization of enal-tethered cyclohexadienone by exploiting the reactivity of a simple Jørgensen-Hayashi catalyst through the merging of iminium and enamine activation. This asymmetric desymmetrization reaction has broad substrate scope in good yields with high to excellent enantioselectivity. DFT calculations suggest that the elimination of the alkoxy group is the rate-limiting step and that it proceeds through proton abstraction by solvent instead of a direct 1,3-proton shift.
RESUMEN
The expeditious construction of complex molecules having multiple stereocentres is highly desirable in organic chemistry. In the present communication, we report the development of an organocatalytic asymmetric desymmetrization of prochiral enal-tethered cyclohexadienones via the C3-selective Friedel-Crafts alkylation of indoles triggered by LUMO-lowering iminium activation/HOMO-raising enamine activation. The reaction provides access to bicyclic enones, which further undergo acid-mediated intramolecular annulation from C2-position to afford highly strained cyclohepta[b]indoles with five contiguous stereocentres and three new C-C bonds in excellent enantioselectivity and diastereoselectivity.
RESUMEN
The enantioselective desymmetrization via remote C(sp2)-H amidation of the prochiral 2,2-disubstituted cyclopentene-1,3-dione with N-methoxybenzamide has been developed. The overall process was catalyzed by a chiral bifunctional thiourea catalyst through a sequential conjugate-addition-elimination-tautomerization. This strategy provides rapid access to highly functionalized five-membered carbocycles, bearing an all-carbon quaternary stereogenic center through remote stereocontrol in high yields with moderate to excellent enantioselectivities.