"Chloroiodomethane on treatment with methyllithium-lithium bromide or n-butyllithium at low temperature undergoes lithium iodide exchange to form a lithium chlorocarbenoid species [LiCH2Cl]. This highly reactive "carbanion" intermediate can be intercepted by the carbonyl group of aldehydes or ketones before it undergoes α-elimination to generate carbene and LiC1. Displacement of chloride from the initially formed carbonyl adducts furnishes the corresponding epoxides in high yields."