Stereoselective catalytic synthesis of 3‐trifluoromethyl indolines through the [4+1] cycloaddition of benzoxazinones and sulfur ylides in a transition‐metal‐free manner was developed. In the presence of a catalytic amount of sodium hydride, aza‐ortho‐quinone methide intermediates were formed from trifluoromethyl benzoxazinones through decarboxylation after the first nucleophilic attack of sulfur ylides