Studies of Azetidin-2-one as a Reactive Enolate Synthon of β‑Alanine for Condensations with Aldehydes and Ketones

Studies
describe formation of the lithium enolate of N-(4-methoxybenzyloxy)­azetidin-2-one
(1) and characterization
of representative aldol reactions with aldehydes and ketones. Diastereoselectivity
features the production of anti-aldol adducts from
α,β-unsaturated ketones and α-branched aliphatic
aldehydes. The stereoselectivity is rationalized via closed, six-membered
transition-state arrangements leading to the formation of Felkin–Anh
and anti-Felkin products. Examples illustrate the
direct incorporation of monocyclic β-lactams into a variety
of molecular architectures. The utility of 1 as an enolate
synthon of homoglycine (β-alanine) is illustrated by the efficient
synthesis of novel β-amino acid derivatives, including complex
4-hydroxy-2-pyridinones.