Both nonracemic 3-pyrrolines and 2,3-cis-2-vinylaziridines have been synthesized selectively from common (Z)-allylic alcohols by simply changing the leaving group and the reaction conditions. Whereas treatment of (Z)-allylic mesylates with NaH yields exclusively 3-pyrrolines in high yields, exposure of allylic methyl carbonates to a catalytic amount of Pd(PPh3)(4) affords 2,3-cis-2-vinylaziridines diastereoselectively in high yields. A simple synthesis of (S)-3,4-dehydroproline starting from (R)-serine is also described.