Grubbs-type ruthenium initiators have found extensive use in complex polymer synthesis but are greatly limited to the nonfunctional derivatives that are commercially available. This report describes the design of functional enyne molecules that rapidly and efficiently convert the third-generation Grubbs catalyst (G3) into a variety of custom initiators for use in polymer synthesis. The identification of electron-deficient sulfonamide derivatives enables high conversion efficiency (>98%) to functional initiator structures with a minimal number of enyne equivalents (2.5-3 equiv). The catalyst transformations are complete in minutes at room temperature and can be directly used in polymerization without intermediate purification. Through combination with existing termination methods, this technology gives practical entry into well-defined heterotelechelic polymers using metathesis polymerization.