[3,3]-Sigmatropic Rearrangement/Allylboration/Cyclization Sequence: Enantioenriched Seven-Membered-Ring Carbamates and Ring Contraction to Pyrrolidines
Abstract
The combination of in situ generated α-isocyanato allylboronic esters and aldehydes afforded seven-membered-ring enecarbamates with high levels of diastereo- and enantiocontrol. They were easily converted into diversely substituted 1,3-oxazepan-2-ones. An unprecedented rearrangement of 5-acetoxy-7-aryl or styryl derivatives led to tetrasubstituted pyrrolidines. A computational study provides evidence on the feasibility of the proposed mechanism of this unusual ring contraction