Palladium‐Catalyzed Cascade for Rapid Access to Tetrahydro‐4H‐pyrazolo[3,4‐d]pyrrolo[1,2‐a]pyrimidin‐4‐one Tetracyclic Fused Heterocycles

The cascade reaction is an attractive strategy for building fused heterocycles. We report the first synthetic methodology to construct (6R)‐6‐hydroxy‐1,3a,6,11a‐tetrahydro‐4H‐pyrazolo[3',4':4,5]pyrimido[2,1‐a]isoindol‐4‐one fused heterocycles based on a cascade sequence of Suzuki coupling to form a C–C bond and base‐mediated intramolecular cyclization to form a C–N bond. This protocol exhibits high stereospecificity, as intramolecular cyclization generates a chiral center with exclusive R‐configuration in the product. A mechanism for the cascade reaction is proposed based on density functional theory calculations.