A new method for oxidation of sulfides to sulfoxides with molecular bromine on a solid silica gel support has been developed. This procedure cleanly oxidizes sulfides to the corresponding sulfoxides in excellent yields. To our knowledge, this is the first example of oxidation of sulfides by molecular bromine in dichloromethane that does not require the presence of a base or another reagent to scavenge the byproduct hydrogen bromide in order to prevent side reactions. The reported procedure is simple, fast, product isolation is trivial, and it produces excellent yields.The biggest disadvantage of the utilization of bromine in the oxidation of sulfides was undesired side reactions that often predominated over sulfoxide formation. 1 Cleavage of the C-S bond and bromination of the sulfide substrate at various positions are two unwanted reactions observed in this oxidation process. Hydrogen bromide is considered responsible for these unwanted side reactions. Procedures that produced limited success in preventing these side reactions utilized either a complex of bromine and an amine in aqueous acetic acid media, or are carried out in a biphasic medium (CH 2 Cl 2 /H 2 O) using potassium hydrogen carbonate or pyridine as the hydrogen bromide acceptor. 2 Another procedure involved treatment of the reaction mixture with hexabutyldistannoxane in order to suppress the formation of sulfones. 3 Although these reactions have some success in preventing undesired side reactions, they are less attractive because they require additional steps in the preparation of the bromine-amine complexes or utilize a toxic reagent. In addition, reactions in aqueous media produce low product yields. This demonstrates the need for a simple and efficient method for conversion of sulfides to the corresponding sulfoxides with molecular bromine.We have recently demonstrated that sulfides can be oxidized to sulfoxides or sulfones on hydrated silica gel employing magnesium monoperoxyphthalate (MMPP) as the oxidant in dichloromethane solvent. 4 In this paper, we demonstrate that bromine can also be utilized as the oxidant for conversion of sulfides to the corresponding sulfoxides on hydrated silica gel utilizing dichloromethane as the solvent. Use of hydrated silica gel as solid support for this oxidation reaction offers many advantages. These include: (1) dichloromethane can be utilized as the reaction media instead of water which was traditionally employed in the oxidation reactions with bromine; (2) hydrated silica gel activates the oxidation reaction by dispersing the oxidant, which is reflected in the very short reaction time for oxidation of sulfides with bromine supported on silica gel compared to the longer reaction time for non-silica gel supported reactions; 3 and (3) hydrated silica gel support eliminates laborious aqueous workup of the reaction, as the solid support, and the byproduct of the oxidant are all easily removed by filtration. In addition, bromine is an inexpensive and readily available reagent. In this procedure, a dichloromethane...
A synthesis of the sesquiterpene sterpurene is presented. Key steps include a 4+3 cycloaddition reaction and a quasi-Favorskii rearrangement. [reaction--see text]
Generation of Cyclopentadienones from 2-Bromocyclopentenones. -Treatment of 2-bromocyclopentenones with NEt 3 leads to cyclopentadienones which spontaneously undergo dimerization in a regio-and completely diastereoselective manner. The dimers can easily be transformed into indanones.
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