Issue in Honor of Prof. Keith Smith ARKIVOC 2012 (vii) 274-281
photobromination of naphthalene leads to trans,trans,trans-tetrabromide 4,9a photobromination
10
of 1,4-dibromonaphthalene 2 affords compound 3. On the other hand, bromination of
9b
naphthalene 1 at -30 ºC produces compound 2.
We have developed a new strategy for the preparation of 1,4-dihydroxytetralins (and similarly their anthracene counterparts) by silver–induced hydrolysis of 1,2,3,4-tetrabromotetralins, which are good precursors for the synthesis of naphthalene (or anthracene) epoxides.9c-f These studies showed that such 1,4-dihydroxy compounds are useful intermediates for polyfunctionalisation of aromatic compounds (Scheme 1). Thus, base-induced dehydrobromination of 6 produces the epoxide 7. By contrast, similar treatment of 8, obtained from the hexabromide 5, gives the aromatized product 9. Recently, in the case of a 1,4-dihydoxy-3,4dibromoanthracene, we showed that dehydrobromination led to a product that was neither aromatized nor contained an epoxide unit.9g
In this paper we describe the application of silver-induced hydrolysis to compound 3, which led to a synthesis of 2,5,8-tribromonaphthoquinone (12) in four steps starting from naphthalene.
Br Br OCH3 Br
Br2/hv CCl4, 25 oC
Br
Br
Br 41 Br 9
Br2
CH3ONa
CH2Cl2, -30 oC
THF, -25 oC
dark Br Br Br Br OCH3 Br
Br
Br2/hv Br CCl4, 25 oC
Br
Br OCH3
Br Br Br
32
Br2 8
CH2Cl2
Ag2SO4
-15 oC, dark
MeOH, 25 oC Br
Br OH
Br Br
O
1
Br
Br
AgClO4/H2O THF, 25 oC
CH3ONa 2 THF, 25 oC
3 Br
Br
4
O
Br OH
Br Br Br
65
7
Scheme 1. Transformations of bromonaphthalenes.
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