Enantiomerically enriched beta-(diphenylphosphatoxy)nitroalkanes undergo radical ionic fragmentation, induced by tributyltin hydride and AIBN in benzene at reflux, to give alkene radical cations in contact radical ion pairs. These contact ion pairs are trapped intramolecularly by amines to give pyrrolldines and piperidines with significant enantloselectivity (similar to60% ee), indicative of cyclization competing effectively with equilibration within the ion pairs. Use of an intramolecular N-propargylamine as a nucleophile provides an enantiomerically enriched pyrrolizidine skeleton via a tandem polar/radical crossover sequence.
Copper(I)-Catalyzed Intramolecular Hydroalkoxylation of Unactivated Alkenes
A Cu(I)-Xantphos system catalyzed the intramolecular hydroalkoxylation of unactivated terminal alkenes, giving five- and six-membered ring ethers. This system is applicable to both primary and secondary alcohols. A reaction pathway involving the addition of the Cu-O bond across the C-C double bond is proposed. A chiral Cu(I) catalyst system based on the (R)-DTBM-SEGPHOS ligand promoted enantioselective reaction with moderate enantioselectivity.