Conjugate Addition of Lithium N-Phenyl-N-(α-methylbenzyl)amide: Application to the Asymmetric Synthesis of (R)-(-)-Angustureine

The conjugate addition of lithium (R)-N-phenyl-N-(alpha-methylbenzyl)amide to a range of alpha,beta-unsaturated 4-methoxyphenyl esters proceeds with excellent levels of diastereoselectivity to give the corresponding beta-amino esters in good yield and as single diastereolsomers (> 99:1 dr). The synthetic utility of this methodology has been demonstrated via the short and concise asymmetric synthesis of the tetrahydroquinoline alkaloid (R)-(-)-angustureine in six steps and 32% overall yield from commercially available oct-2-enoic acid.