A silver‐catalyzed [5+1] annulation of o‐acylaryl isocyanides with ammonium acetate and hydroxlamine was developed for the efficient and practical synthesis of quinazolines and quinazoline 3‐oxides in good to excellent yields, respectively. The domino process involved an unprecedented isocyanideinsertion into the N−H bond of ammonia or hydroxylamine and followed by condensation reaction at ambient