[63256-88-2] · C24H54O2Sn2 · Bis(tributyltin) Peroxide · (MW 612.07)
(mild nonalkaline source of dinucleophilic peroxide; reacts with alkyl triflates to deliver dialkyl peroxides, often in higher yields than obtained from the reaction of alkyl mesylates with hydrogen peroxide and a base)
Physical Data: unstable liquid.
Solubility: sol CH2Cl2.
Form Supplied in: must be freshly prepared.
Preparative Method: addition of Tri-n-butyl(methoxy)stannane to an ether-methanol solution of anhydrous Hydrogen Peroxide at 0 °C followed by removal of ether and methanol in vacuo at 0 °C.1
Purification: attempted purification by rapid column chromatography on silica gel or Florisil led to decomposition.
Handling, Storage, and Precautions: thermally unstable, but can be stored for 1 day neat at -20 °C. The reagent is presumed to be a strong oxidizing agent and, as with organic peroxides in general, there is a potential for explosion. The use of a safety shield is mandatory during preparation and use. Reaction with water releases anhydrous H2O2 that is hazardous.
Bu3SnOOSnBu3 reacts with alkyl triflates to generate dialkyl peroxides in good yields. In many cases, as in the reaction with isopropyl triflate (eq 1), dialkyl ethers are formed as byproducts. Other syntheses of secondary dialkyl peroxides give significantly lower yields. For example, base-catalyzed alkylation of hydrogen peroxide with isopropyl mesylate gives diisopropyl peroxide in low yield (eq 2).2 Silver(I) Trifluoroacetate-assisted alkylation of 2-butyl hydroperoxide with 2-butyl bromide gives a low yield of dialkyl peroxide (eq 3).3
Cyclic dialkyl peroxides are obtained from the reaction of alkyl ditriflates with Bu3SnOOSnBu3 (eq 4). For volatile dialkyl peroxides, isolation is simplified and yields improved by using 1,2,4-trichlorobenzene as solvent. The reaction is conducted in vacuo, and the product is efficiently removed from the reaction mixture and collected in a cold trap (-78 °C). This protocol is essential for the preparation of 2,3-dioxabicyclo[2.2.1]heptane, the strained nucleus of prostaglandin endoperoxides, because this peroxide is unusually reactive (eq 5). It is noteworthy that pure 2,3-dioxabicyclo[2.2.1]heptane, mp 63-64 °C, is stable toward bis(tri-n-butyltin) peroxide.
An ether, tetrahydropyran, is the major product of the reaction of Bu3SnOOSnBu3 with pentane 1,5-bistriflate. The relative preference for cyclic ether formation in the reaction of bistriflates is 5, 6 > 7 > 8-membered rings while that for cyclic peroxide formation is 4 &LLt; 5, 6 > 7-membered rings. The product ratios of cyclic peroxide versus cyclic ether indicate an important role for stereoelectronic preferences in the kinetically controlled partitioning of a monoalkylperoxytin precursor between two oxonium ion intermediates (eq 6).4
Robert G. Salomon
Case Western Reserve University, Cleveland, OH, USA