Abstract
Phosphorylated α-hydroxyallenes 1 and 2 were smoothly converted into the corresponding 2,5-dihydrofurans 3 and 4 in an 5-endo-trig cycloisomerization reaction by using 5 mol % of coinage metal salts as catalyst. Experimental conditions such as the type of the solvent, the reaction temperature, the mol % and the type of the catalyst were optimized. This mild and efficient cyclization method can be applied to dimethyl 1-hydroxyalkyl-alka-1,2-dienephosphonates 1 and 2-diphenylphosphinoyl-2,3-dien-1-ols 2a–c and 3-diphenylphosphinoyl-3,4-dien-2-ols 2d,e, furnishing 3-phosphorylated 2,5-dihydrofurans 3 and 4 in very good yields.
Highlights
Phosphorylated α-hydroxyallenes 1 and 2 were smoothly converted into the corresponding 2,5-dihydrofurans 3 and 4 in an 5-endo-trig cycloisomerization reaction by using 5 mol % of coinage metal salts as catalyst
Molecules 2015, 20 and represent pivotal structural elements in a wide variety of different biologically active molecules. They can be found in mycotoxins such as verrucosidine [4] and the structurally related citreoviridine [5], as well as vitamin A metabolites [6], polyether antibiotics [7,8], spiroketals [9] and even amino acids [10]. 2,5-Dihydrofurans are important intermediates in organic synthesis due to the presence of the C=C bond as well as the five-membered ring
We present recent results of ongoing studies dedicated towards the optimization of the experimental conditions and the catalyst efficiency in the coinage metal salts-catalyzed cycloisomerization of α-hydroxyalkyl-allenephosphonates and phosphine oxides to 3-phosphorylated 2,5-dihydrofurans, which strongly improve the scope of this method
Summary
Phosphorylated α-hydroxyallenes 1 and 2 were smoothly converted into the corresponding 2,5-dihydrofurans 3 and 4 in an 5-endo-trig cycloisomerization reaction by using 5 mol % of coinage metal salts as catalyst. Experimental conditions such as the type of the solvent, the reaction temperature, the mol % and the type of the catalyst were optimized. 2,5-Dihydrofurans and their derivatives are structural subunits frequently found in a wide variety of natural products which find application as flavor and fragrance compounds and pharmaceuticals [1,2,3]. Several diethylphosphono-substituted α-allenic alcohols [45] and glycols [46] were prepared by Brel [47,48]
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