Intramolecular cyclizations of imines bearing the 2-(thiomethyl)-3-trimethylsilyl-1-propenyl terminator. An efficient new procedure for the stereocontrolled synthesis of functionalized pyrrolidine derivatives

Stereoselectivity in N-Iminium Ion Cyclization: Development of an Efficient Synthesis of (±)-Cephalotaxine

A stereoselective N-iminium ion cyclization with allylsilane to construct vicinal quaternary-tertiary carbon centers was developed for the concise synthesis of (±)-cephalotaxine. The current strategy features a TiCl4-promoted cyclization and ring-closure metathesis to furnish the spiro-ring system. The stereochemical outcome in the N-acyliminium ion cyclization was rationalized by the stereoelectronic effect of the Z- or E-allylsilane. Two diastereomers arising from the cyclization were merged into the formal synthesis of (±)-cephalotaxine.

A rapid and general method for the asymmetric synthesis of 2-substituted pyrrolidines using tert-butanesulfinamide

A new method for the asymmetric synthesis of 2-substituted pyrrolidines in three steps from commercially available starting materials is described. Addition of the Grignard reagent prepared from 2-(2-bromoethyl)-1,3-dioxane to N-tert-butanesulfinyl aldimines proceeds in high yields and with good diastereoselectivities. The sulfinamide products are then cleanly converted into pyrrolidines in one step.

A concise synthesis of turneforcidine via a metalloiminium ion cyclization terminated by the 2-(methylthio)-3-(trimethylsilyl)-1-propenyl moiety

A concise synthetic route to racemic turneforcidine (1) is described that relies on the stereocontrolled cyclization of the 2-(methylthio)-3-(trimethylsilyl)-1-propenyl bearing imine 5 in the presence of TiCl(4). Reaction: see text.