Highly Stereoselective Synthesis and Rearrangement of ,&Amino a-Bromo Chalcones J. C. Arnould, A. Feigenbaum, and F. Henin Laboratolre d e Photoch~mie,U.E.R. Sciences B.P. 347, 51062 Reims Cedex, France Stereoselective reactions are increasingly important in organic chemistrv and so require a corresponding emuhasis in teaching. We propose h e r e a n experimint for advanced students which involves a sequence of easy steps illustrating important reactions as wellas concepts of org&ic chemistry All these reactions (see the figure) can be performed during a single day. Addition of bromine to chalcone IE (Reaction A) leads to t h e (*) erythro 2,3-dibromo 1,3-diphenylpropan 1-one, II. Reaction of II with two equivalents of piperidine affords (f) threo 2-bromo 3-piperidino 1,3-diphenylpropan 1-one, I I I . This reaction is suggested to proceed via dehydrobromination t o enone I V E which then undereoes Michael addition of oiperidine to yield threo-III. This uathwav is suouorted hv isolation of enone WE after treatingerythro-11 with a weak base (Reaction C). When this compound is then subjected to the reaction conditions of (B), threo-III is again isolated (Reaction D). T h e observed stereospecificity is suggested to result from protonation on the less hindered face of the Michael addition e n d , VIII, opposite t o t h e phenyl group1 (la):
Reactions C and D. a-Bromo Chalcone WE (I b) A mixture of dibramochalcone2 (0.013 mole, 5 p), sodium acetate 10.018 mole, 1.5 g) and 95%ethyl alcohol (13 ml) is refluxed for 4 hr. The solvent is evaporated, and the residue is dissolved in ether and water. The organic layer is washed with 5%NaHCO:,.
( 5 ) 0% Synth.,coll. Volume I. 2nd Ed., John Wile,, and Sons. New Yurk, 1941, 205
