Antimony(v) cations for the selective catalytic transformation of aldehydes into symmetric ethers, α, β-unsaturated aldehydes, and 1, 3, 5-trioxanes. Issue 27 (21st June 2016) - Arias Ugarte, Renzo
Abstract : 1-Diphenylphosphinonaphthyl-8-triphenylstibonium triflate ([2 ][OTf]) was prepared in excellent yield. This antimony(v ) cation was found to selectively catalyze the transformation of aldehydes into symmetric ethers, α, β-unsaturated aldehydes, and 1, 3, 5-trioxanes. Abstract : 1-Diphenylphosphinonaphthyl-8-triphenylstibonium triflate ([2 ][OTf]) was prepared in excellent yield by treating 1-lithio-8-diphenylphosphinonaphthalene with dibromotriphenylstiborane followed by halide abstraction with AgOTf. This antimony(v ) cation was found to be stable toward oxygen and water, and exhibited exceptional Lewis acidity. The Lewis acidity of [2 ][OTf] was exploited in the catalytic reductive coupling of a variety of aldehydes into symmetric ethers of typeL in good to excellent yields under mild conditions using Et3 SiH as the reductant. Additionally, [2 ][OTf] was found to selectively catalyze the Aldol condensation reaction to afford α-β unsaturated aldehydes (M ) when aldehydes with 2 α-hydrogen atoms were used. Finally, [2 ][OTf] catalyzed the cyclotrimerization of aliphatic and aromatic aldehydes to afford the industrially-useful 1, 3, 5 trioxanes (N ) in good yields, and with great selectivity. This phosphine–stibonium motif represents one of the first catalytic systems of its kind that is able to catalyze these reactions with aldehydes in a controlled, efficient manner. The mechanism of these processes has been explored both experimentally and theoretically. In all cases the Lewis acidic nature of the antimony(v ) cation was found to promote these reactions.