Catalytic cycloalumination in steroid chemistry II: Selective functionalization of 2′-methylidene-2′,3′-ethano-(5α)-cholestane

The catalytic cycloalumination of 2′-methylidene-2′,3′-ethano-(5α)-cholestane with Et₃Al catalyzed by Cp₂ZrCl₂ was performed for the first time to give spiro2′,3′-ethano-(5α)-cholestane-2′,3″-aluminacyclopentane] in a ～75% yield and with high stereoselectivity (>98%). The obtained cyclic organoaluminum compound was transformed in situ into heterocyclic spiran derivatives of 2′,3′-ethano-(5α)-cholestane.