Palladium(II)-Catalyzed Reactions of Allenes with Lithium Bromide and Cyclization of ?-Amino Allenes to Pyrrolines

Abstract: This thesis is based on three novel palladium(II)-catalyzed reactions of allenes with lithium bromide and a bromonium ion induced cyclization of allenyl amides to pyrrolines. In Paper I a 1,2-functionalization of allenes is presented where bromide adds as a first nucleophile followed by intramolecular attack by an oxygen or nitrogen nucleophile. Chapter 2 deals with the extension of this reaction to different nitrogen nucleophiles such as urea, carbamate, and N-tosyl carbamate providing access to substituted pyrrolidines and oxazolidines in good yields under mild reaction conditions.Paper II deals with a stereoconvergent, palladium(II)-catalyzed SN2’ reaction of ?-acetoxy allenes with bromide as nucleophile. In this reaction substituted (Z,E)-2-bromo-1,3-dienes are produced in good yields with excellent diastereo-selectivity.Paper III describes a mild racemization reaction of chiral allenes. The effect of the functional group present in the molecule on the reaction rate is examined. All these reactions published in Papers I-III proceed through a common intermediate: a 2-bromo-(?-allyl)palladium complex.The fourth paper describes a simple, efficient, and enantiocontrolled cyclization of N-protected ?-allenyl amines with N-bromosuccinimide (NBS) to afford 3-bromo-pyrrolines. The synthesis of optically active 2,5-dehydroprolinol derivative is also described. The mechanism, scope, and limitations of all four reactions are discussed in this thesis.