Tunable Dimerization and Trimerization of β‐Alkynyl Ketones via Silver Catalysis for Accessing Spiro and Dispiro Compounds Containing 1 H ‐Isochromene

New silver‐catalyzed tunable dimerization and trimerization reactions of β‐alkynyl ketones have been established, enabling multiple C−C bond‐forming events to selectively access skeletally diverse spiroisochromenes with generally good yields. The silver‐enabled bicycloaddition of β‐alkynyl ketones with water offered hydroxylated spiroisochromenes. Without water, spiroisochromenes with a methylene moiety were obtained through catalytic 6‐ endo‐dig oxo ‐cyclization/[4+2] cycloaddition cascades by using pyridine as additive whereas employment of 1,1′‐binaphthyl‐2,2′‐diyl hydrogen phosphate (BiNPO 4 H) as a Brønsted acid catalyst rendered the unprecedented dispiro trimerization products through double C( sp 3 )–H functionalization.