Lithium Enolates Derived from Pyroglutaminol: Mechanism and Stereoselectivity of an Azaaldol Addition.

ABSTRACT: A lithium enolate derived from an acetonide-protected pyroglutaminol undergoes a highly selective azaaldol addition with (E)-N-phenyl-1-[2-(trifluoromethyl)phenyl]methanimine. The selectivity is sensitive to tetrahydrofuran (THF) concentration, temperature, and the presence of excess lithium diisopropylamide base. Rate studies show that the observable tetrasolvated dimeric enolate undergoes reversible deaggregation, with the reaction proceeding via a disolvated-monomer-based transition structure. Limited stereochemical erosion stems from the intervention of a trisolvated-monomer-based pathway, which is suppressed at low THF concentrations and elevated temperature. Endofacial selectivity observed with excess lithium diisopropylamide (LDA) is traced to an intermediate dianion formed by subse

SUBMITTER: Houghton MJ 

PROVIDER: S-EPMC5240537 | biostudies-literature | 2016 Aug

REPOSITORIES: biostudies-literature