A weak Bronsted acid-catalyzed asymmetric guanidine aza-conjugate addition reaction has been developed. C-2-symmetric, dual hydrogen-bond donating bistriflamides are shown to be highly effective in activating alpha,beta-unsaturated esters toward the intramolecular addition of a pendant guanidinyl nucleophile. Preliminary mechanistic investigation, including density functional theory calculations and kinetics studies, support a conjugate addition pathway as more favorable energetically than an alternative electrocyclization pathway. This methodology has been successfully applied to the synthesis of the 3,4-dihydroquinazoline-containing antiviral, Letermovir, and a series of analogues.