75630-75-0Relevant articles and documents
Routes to 3-Bromoflavanone from erythro-2'-Hydroxychalcone Dibromide: Spectral and Kinetic Evidence for the Dominating Role of Elimination-Addition Sequences via (E)- and (Z)-α-Bromo-2'-hydroxychalcones
David, Shantha K.,Main, Lyndsay,Old, K. Barry
, p. 1367 - 1373 (2007/10/02)
Rate coefficients for the formation from erythro-2'-hydroxychalcone dibromide of (E)- and (Z)-α-bromo-2'-hydroxychalcone and for their cyclisation to 3-bromoflavanone in 4 : 1 water-ethanol at pH 7.88 are established by a combination of kinetic and spectrophotometric measurements.The E-isomer is formed in a yield (percent) of 35 +/- 2 as opposed to 63 +/- 8 for the Z-isomer.The Z-isomer cyclises over 20 times faster.Direct cyclisation of the dibromide, if any, is only a very minor route to 3-bromoflavanone.The implications for the elimination mechanism of the preference for syn- over anti-elimination, of the independence of rate of buffer (N-ethylmorpholine) concentration, and of the effect of pH change are briefly considered.Mechanisms discounted are E2 with N-ethylmorpholine or solvent molecules as base, and E1.No firm assignment is possible amongst a number of other mechanisms.