sample was worked up in the usual manner and the nmr spectra were recorded in CDC13.Attempted Reactions of 2a-c with Hydrazoic Acid. Sodium azide (0.02 mol) was allowed to react with a slight excess of hydrobromic acid in 50 ml of DMF at room temperature for 10 min. Then 0.02 mol of 2a-c was added and the mixture was stirred for the same time as given in procedure B. The nmr spectra, after work-up, indicated no reaction. The -bromovinyl ketones 2a-c were recovered in 76-86% yield.Dehydrobromination of la-c. Dibromides la-c (0.1 mmol) and 0.2 mol of sodium acetate were stirred in 200 ml of dry DMF at room temperature for the appropriate reaction time (0.5 hr for la, 5 hr for lb, and 1 hr for lc). After work-up the following yields were obtained: 90% 2a in a cis/trans ratio of 80/20, 90-92% cis-Vo, and 89% 2c in a cis/trans ratio of 60/40.Cis-trans Isomerization of Vinyl Bromides 2. cfs-a-Bromoethylideneacetophenone (2a) isomerized spontaneously and quantitatively into trails-2a (mp 66.5-67.0°, petroleum ether) within 1 day upon standing at room temperature. When rá-a-bromochalcone (2b) was heated under nitrogen at ca. 160°for 1 hr, the nmr spectrum showed a large decrease of the 2.87 absorption relative to the aromatic multiplet indicating a cis/trans ratio of about 30/70. This reaction mixture was allowed to crystallize from zz-hexazie at low temperature, and yielded trans-2b as a pale yellow crystalline product, mp 38-39°( lit.10 mp 42°).
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