Nuclear bromination in phloroglucinol derivatives

TetrahedronLettera No.19, pp. l-3, 1959. Pergamon Press Ltd. Printed in Great Britain.

NUCLFAR EXMINATION IN PBLOROGLUCINOLDERIVATIVES John A. Donnelly Department of Chemistry,University College, Dublin (Received. 30 October 1959)

SINCE Koataneoki and Tembor' reported nuclear substitutionin the bromination of chalconee derived from phloroglucinol(m,

I), rorlcere2'3'4

have aesumed that it occurs in the 5'-positionto form a tribromidewhich gives the 5-bromoaurone(II) with aqueoue ethanolio potaeeium hydroxide.

(J O,,,Q

“~pLC”(-J

CH,O /

Br

-

A

3

3I

I

.w

cyo / Br I

0”;

0

cd

0

-

\

Dr.

' St. v. Kostanecki and J. Tambor, &

&

2260 (1899).

2 lV..P.Cullinane and D. Philpott, J. Chem. Soo, 1761 (1929). 3 D. R. Nadkrni and T. S. Wheeler, J. Univ. Bomber. 2, 107 (1937). 4 W. A. Hutchine and T. S. Wheeler, J. Chem. Sot, 91 (1939). 1

No.19

Nuclear brominationin phloroglucinolderivatives

It has now been found that the halogen atom enters in fact the jl-position,so that the compounds previously formulatedas in II exe actually of type III. Wheeler (this department)has suggested that the resulting steric effects on the 2'-hydroxylgroup facilitate the hitherto inexplicableformation of aurone rather then of the correspondingflavone from the so-called 5'-(actuallyjt-)bromochalcones.

OH

COXH, CH,O Ip

,p t -

CH,O XII

CH,O mI

Br CH,O/ OH CH,OOCOCH, \ CYO.;

:

Ii

The monobrominatedcompound5 (VII), obtained from 2-hydroxy-4,6?' dimethoqyacetophenone(IV), gave VIII, m.p. 147-149' (ethsnolicferric colour - green), when treated with alkaline potassium persulphate. Compound VIII on further methylationyielded IX which was identical (mixed melting point) with authentic j-brcmo-2-hydroxy-4,5,6-trimethoxyacatophen-one ferriF.icol-ou%?.i green), preps;Fed by (Ix), m.p, 89-90" (-eth&nol‘ic

5 A. R, ,PenfolQ J;,Pro.av6:Roy.: SCN...N,S.W, 2,

184 (l92T).,

No.19

Nuclear bromination in phloroglucinolderivatives

3

brominating 2-hydroxy-4,5,6-trimethoxyacetophenone (VI).6 Bromination of 2,5-dihydroxy-4,6-dimethoxyacetophenone (V),b for comparisonwith VIII, was unsuccessful. 7 m.p, 185-1870 , prepared j~-Bromo-2'-hydroxy-41,6~-dimethoxychalcone, from VII, and benzaldehydewas identicalwith the chalcone obtained by treating the tribrominatedproduct of I with potassium iodide in acetone. Satisfactoryanalyses were obtained for compoundsVIII and IX. The author wishes to thank Professor T. S. Wheeler for his interest and advice.

6

V. D, N. Sastri and T. R. Se&a&i,

Proc. Indian Aoad, Sci, 22, 262 (1946). 7 N. R. Bannerjee and T. R. Seshadri, Proc. Indian Acad. Sci, 29, 134 (1952).