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-(α-methylbenzyl)amide to a range of α,β-unsaturated 4-methoxyphenyl esters proceeds with excellent levels of diastereoselectivity to give the corresponding β-amino esters in good yield and as single diastereoisomers (>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.