My PhD dissertation - Institut Fresnel
My PhD dissertation - Institut Fresnel
My PhD dissertation - Institut Fresnel
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4.1 Preparation of Enantiomerically Pure 6,6’-<br />
Dibromobiphenyl-2,2’-diol and Derivatives Thereof<br />
Since A. Rajca et al.<br />
[ 172]<br />
40<br />
described the preparation of 2,2',6,6'-<br />
tetrabromobiphenyl (30) in two step with a very low overall yield (31%), synthesis of<br />
biphenyl 30 was first attempted in a one step procedure. The oxidative coupling of 2-<br />
hydroxynaphtalene with iron(III) chloride to form 2,2'-dihydroxy-1,1'-binaphtyl (BINOL)<br />
inspired this investigation and suggested the use of different metallic oxidants. For this<br />
purpose, commercially available 1,3-dibromobenzene was first metalated at -75 °C with<br />
lithium diisopropylamine (LIDA) in tetrahydrofuran to selectively afford 1,3-dibromo-2-<br />
lithio-benzene<br />
[ ] 174 . The transient species produced was then treated with various salts such as<br />
iron(III) chloride or chromium(III) chloride at -75 °C, but the yield of biphenyl 30 was<br />
unfortunately very low (8 to 14%) or even not existent. As the reaction effectively happened<br />
but appeared to be sluggish at low temperature, the transient lithio- species was<br />
transmetalated to its organozinc derivative by addition of anhydrous zinc(II) bromide at<br />
-75 °C. The latter, more stable towards aryne formation, could hence be warm up to 0 °C and<br />
treated with iron(III) chloride to afford 30 in 33% yield. However low, this yield remained<br />
unoptimized and offers the promising advantage to produce the halogenated biphenyl in one<br />
step.<br />
LiC 4H 9, THF<br />
Br Br - 75 °C Br Br<br />
Li<br />
[ ] 173<br />
ZnBr 2, - 75 °C FeCl 3, O °C<br />
Br Br<br />
Br Br<br />
Br Br<br />
ZnBr<br />
30, 33%<br />
2,2',6,6'-Tetrabromobiphenyl (30) was, in parallel, efficiently prepared in two steps<br />
from 1,3-dibromobenzene, following F. Leroux's modification [53] of the procedure described<br />
by A. Rajca et al. [172] . The previously metalated 1,3-dibromobenzene was first treated with<br />
iodine to afford 1,3-dibromo-2-iodobenzene (29) in nearly quantitative yield (96%).<br />
LIDA, THF I 2, THF<br />
Br Br<br />
- 75 °C<br />
Br Br<br />
Br Br<br />
Li<br />
I<br />
29, 96%