Ketones and aldehydes are employed as enol O-nucleophiles in an iridium-catalyzed asymmetric allylic substitution reaction. The reaction proceeds well in the presence of a well-defined chiral iridium complex under mild conditions. A series of chiral 2H-1,4-oxazine skeletons can be obtained in up to 94% yield with 99% ee. The utility of this novel method has been demonstrated by its implementation in the first enantioselective synthesis of (+)-chelonin A.