An Expeditious Route to 1α,25-Dihydroxyvitamin D<sub>3</sub>and Its Analogues by an Aqueous Tandem Palladium-Catalyzed A-Ring Closure and Suzuki Coupling to the C/D Unit
mild, general, and highly stereoselectivePd0‐catalyzed cascade to the triene system of the hormone 1α,25‐dihydroxyvitamin D3 and six representative analogues is reported. The intramolecular cyclization of an enol–triflate (lower fragment) followed in situ by Suzuki–Miyaura coupling with an alkenyl boronic ester (upper fragment, also efficiently prepared by Pd0‐catalyzed coupling) in equimolar amounts