[10588-31-5] · C2Br4O · Tribromoacetyl Bromide · (MW 359.64)
Physical Data: bp 86 °C/11 mmHg; d 2.810 g cm-3.
Solubility: sol ether, benzene, toluene.
Form Supplied in: not commercially available.
Purification: can be purified by vacuum distillation.
Handling, Storage, and Precautions: moderately stable at room temperature; should be freshly distilled prior to use. Light-sensitive; should be used and stored with the rigorous exclusion of light.
Tribromoacetamides have been prepared by the reaction of tribromoacetyl bromide with the requisite amine (eq 1).1 The tribromoacetamides so produced are light sensitive and must be used immediately. Photoirradiation of these amides promotes homolytic cleavage and can generate the corresponding dibromo primary radical.3 Alcohols can also be acylated with tribromoacetyl bromide (eq 2).1 However, unless use of the tribromide is absolutely necessary, commercially available Trichloroacetyl Chloride is superior and the corresponding trichloroacetylated products can usually be used in subsequent reactions in the same manner as the tribromoacetylated materials.
Tribromoacetyl bromide can be debrominated with Zinc that has been activated with copper to afford a solution of dibromoketene in ether (eq 3).2 The dibromoketene generated in this manner readily undergoes [2 + 2] cyclization with Cyclopentadiene to give the corresponding cyclobutanone (eq 4).2 Dibromoketene has been used effectively in the synthesis of prostaglandins and other natural products.4,5 Dibromoketene has also been prepared by the elimination of HCl from dibromoacetyl chloride and by reaction of trimethylsilyl tribromoacetate with Triphenylphosphine.6,7 In fact, this latter method is superior for the preparation of dibromoketene as a synthetic precursor, as the subsequent cyclization can be performed in a single reaction vessel (eq 5).7 High yields of the cyclized material are obtained in this manner.
James W. Leahy
University of California, Berkeley, CA, USA