ALUMINUM BROMIDE 1
Aluminum Bromide gated cyclopentenones under mild conditions.4 The diene must
be unsubstituted at the 4-position but substitution at all other
positions is tolerated. This cyclocarbonylation is stereospecific,
AlBr3
depending only on the configuration of the diene complex (eq 3).
Spirocyclic compounds can be formed using an appropriate pre-
[7727-15-3] AlBr3 (MW 266.72)
cursor (eq 4). The method serves as a valuable alternative to the
InChI = 1/Al.3BrH/h;3*1H/q+3;;;/p-3/fAl.3Br/h;3*1h/
intramolecular Pauson Khand reaction. One apparent limitation is
qm;3*-1
that bicyclic cyclopentenones with an angular alkyl group cannot
InChIKey = PQLAYKMGZDUDLQ-CBXPCZPZCJ
be prepared.
(Lewis acid catalyst similar to AlCl3; useful in oxacycle,1 cyclo-
pentanone,3 and conjugated cyclopentenone4 synthesis; halo-
AlBr3
genations;6 reductive deoxygenation of ketones and secondary
O (3)
CO, CH2Cl2
alcohols;7 selective ether cleaving reagent;8 isomerization
20 °C
H
catalyst;12 Friedel Crafts catalyst16) Fe(CO)3 60%
9:1 diast. mixt. 9:1 diast. mixt.
ć% ć%
Physical Data: mp 97 C; bp 268 C; d 3.01 g cm-3.
Solubility: sol CS2, alcohols, ether, acetone, hydrocarbons,
nitrobenzene, Br(CH2)2Br.
Form Supplied in: commercial grade white to yellowish-brown
AlBr3
(4)
deliquescent solid; colorless is pure. Also available as a 1.0 M Fe(CO)3 CH2Cl2
solution in CH2Br2. Exists as a dimer (Al2Br6) in solid and 20 °C
O
60%
liquid phases.
Handling, Storage, and Precautions: use in a fume hood; fumes
strongly in air; violent reaction with H2O; corrosive to skin.
Keep tightly closed and protected from moisture. Decomposes
Halogenations. A novel photochemical ring contraction of
upon heating in air to Br2 and alumina.
1-naphthols to 3-halomethylindanones is promoted by AlBr3 or
AlCl3 (eq 5).5 The halogen substituent is derived from the halo-
genated solvent. In CH2Cl2, chlorides are the major product; in
Oxacycle Synthesis. Unsaturated alcohols react with alde-
CH2Br2, bromides are produced regardless of whether AlBr3 or
hydes in the presence of AlBr3 to give 4-bromooxacycles in a
AlCl3 is used.
stereoselective manner (eq 1).1 Tetrahydropyrans are formed in
the all-cis configuration. Seven-membered rings are produced as
OH
O
a mixture of isomers at the bromide position. This method has
5 AlBr3, h½
a synthetic advantage over similar allylsilane procedures2 in that
(5)
R1
larger rings can be prepared.
CH2Cl2, rt
R2
R1 R2
Br
Cl
R2 CHO
OH
AlBr3
n
(1)
R Thiophenes can be regioselectively brominated by AlBr3 in
CH2Cl2, 0 °C
n
O
R R2
51 78%
the presence of Benzeneseleninyl Chloride (eq 6).6a Furans are
n = 1, 2
halogenated in low yield and pyrroles are unreactive.
Cyclopentanone Synthesis. Ring expansion of 1-acyl-1- AlBr3, PhSeOCl
(6)
(alkyl or arylthio)cyclobutanes to cyclopentantones occurs
CH2Cl2, rt
Br
S S
98%
readily in the presence of 1 equiv AlBr3 (eq 2).3 This method
has been used to provide good yields (68 86%) of 2-, 2,4-,
and 2,5-substituted cyclopentanones. Aluminum Chloride and
Bridgehead halogen exchange in polycyclic substrates is cat-
Iron(III) Chloride were also effective in this conversion; however,
alyzed by AlBr3 in halogenated solvents and proceeds read-
BF3·Et2O and protic acids do not work.
ily in fair to good yield (50 90%).6b For bromination, CH2Br2
or CHBr3 solvent is used. Iodinations are carried out in MeI
R4S
or CH2I2 and chlorinations in CHCl3 or CCl4. Bromoalkyla-
R3
SR4
AlBr3 tion of 1-bromoadamantane occurs when subjected to ethylene
O
R2 (2)
R3 hexane, rt
or vinyl bromide in the presence of AlBr3 to give 1-bromo- or
R2
1,1-dibromo-2-(1-adamantyl)ethane, respectively.6c Yields are
R1
R1 O
dependent on the quality of the AlBr3. Bromination of the
bridgehead position of adamantanone by AlBr3/t-BuBr (so-called
Conjugated Cyclopentenone Synthesis. Decomplexation of  sludge catalyst ) provides an improved, high yielding synthesis
1,3-butadieneiron tricarbonyl complexes by AlBr3 leads to conju- of 1-bromo-4-adamantanone.6d
Avoid Skin Contact with All Reagents
2 ALUMINUM BROMIDE
AlBr3
C O Bond Cleavages. Reductive deoxygenation of ketones
Br Et
CS2 or CCl4
and secondary alcohols to the corresponding methylene hydrocar-
25 °C
Et Et
(10)
B B
bons in excellent yield can be accomplished by the Diisobutylalu-
95%
Et Br
minum Hydride/AIBr3 reagent system.7 In some cases, the addi-
tion of a catalytic amount of Cp2MCl2 (M = Ti, Zr) or Nickel(II)
Diphenylacetylene undergoes dimerization with AlBr3 to give
Acetylacetonate is required. Diaryl, alkyl aryl, or dialkyl ketones
1,2,3-triphenylazulene.15 The yield is very dependent on the purity
and secondary alkyl or benzylic alcohols undergo this reaction but
of AlBr3 used. Yields are enhanced by the addition of a small
primary alcohols or phenols do not.
amount of V2+ or Ni2+, whereas Ti3+, V4+, Cr2+, Cr3+, Fe3+,
Anhydrous AlBr3 in MeCN or CS2 is useful for the removal
or Zn2+ almost completely suppress azulene formation.
of methyl ethers and in some instances selective cleavage is
possible.8 The 5-MeO group in 3,5,6,7-tetramethoxyflavones
Friedel Crafts Reactions. AlBr3 is a superior reagent for in-
and the 3-MeO group in 3,6,7-trimethoxy-5-tosyloxyflavones are
selectively cleaved in nearly quantitative yield without debenzyla- tramolecular Friedel Crafts cyclization of É-phenylalkanoic acid
chlorides (Ph(CH2)nCOCl; n = 8 15) to the paracyclophanes
tion (eq 7).8a It is superior to AlCl3 in some ether cleavages8b since
(eq 11).16a Under high dilution conditions, the yields are generally
it is a stronger Lewis acid and more soluble in organic solvents.
twice as high as that with AlCl3. Negligible yields of medium-
An excellent reagent for phenol ether cleavage (except diphenyl
sized cyclophanes (n = 8, 5.3%) are obtained. Yields tend to in-
ether) is the pyridinium salt of AlBr3.8c
crease with increasing ring size (n = 15, 70%). Other examples of
its use as a Friedel Crafts catalyst and in the Fries rearrangment
MeO O OH O
of phenol esters appear in the literature.16b f
MeO OMe MeO OMe
AlBr3
(7)
O
MeCN
MeO MeO
O Ar O Ar
0 5 °C
O
AlBr3
(11)
Ph (CH2)n Cl
CS2, reflux
AlBr3 is an efficient reagent for epoxide cleavage giving high
(CH2)n
yields of the bromohydrin. It does not show much regioselectivity
in the case of substituted substrates.9 The hydroxylation of cyclic
acetals with Hydrogen Peroxide can be catalyzed by AlBr3 as
well as with other reagents (especially SeBr4) to give esters of the
1. Coppi, L.; Ricci, A.; Taddei, M., J. Org. Chem. 1988, 53, 911.
type RCO2(CH2)nOH (R = H, aryl, alkyl; n = 2 3).10 Disulfide
2. (a) Coppi, L.; Ricci, A.; Taddei, M., Tetrahedron Lett. 1987, 28, 973. (b)
cleavage with AlBr3 has been reported to give cyclized products
Wei, Z. Y.; Li, J. S.; Wang, D.; Chan, T. H., Tetrahedron Lett. 1987, 28,
in certain systems (eq 8).11
3441.
3. Yamashita, M.; Onozuka, J.; Tsuchihashi, G.; Ogura, K., Tetrahedron
Lett. 1983, 24, 79.
S
4. Franck-Neumann, M.; Michelotti, E. L.; Simler, R.; Vernier, J.-M.,
S
AlBr3
Tetrahedron Lett. 1992, 33, 7361.
(8)
PhH
5. Kakiuchi, K.; Yamaguchi, B.; Tobe, Y., J. Org. Chem. 1991, 56,
2
5745.
6. (a) Kamigata, N.; Suzuki, T.; Yoshida, M., Phosphorus Sulfur Silicon
1990, 53, 29. (b) McKinley, J. W.; Pincock, R. E.; Scott, W. B., J.
Am. Chem. Soc. 1973, 95, 2030. (c) Stetter, H.; Goebel, P., Chem. Ber.
Rearrangements. The AlBr3 sludge catalyst has been
1962, 95, 1039. (d) Klein, H.; Wiartalla, R., Synth. Commun. 1979, 9,
extensively used as an effective isomerization reagent in numer-
825.
ous adamantane, diamantane, and triamantane syntheses (eq 9).12
7. Eisch, J. J.; Liu, Z.-R.; Boleslawski, M. P., J. Org. Chem. 1992, 57, 2143.
A wide variety of polycyclic hydrocarbons can be rearranged to
8. (a) Horie, T.; Kawamura, Y.; Tsukayama, M.; Yoshizuki, S., Chem.
these ring systems. Perhydrogenated phenanthrene rearranges to
Pharm. Bull. 1989, 37, 1216. (b) Adams, R.; Mathieu, J., J. Am. Chem.
give mainly trans,syn,trans-perhydroanthracene by the action of Soc. 1948, 70, 2120. (c) Prey, V., Chem. Ber. 1942, 75, 537.
AlBr3/HBr in dimethylcyclohexane.13 9. Eisch, J. J.; Liu, Z.-R.; Ma, X.; Zheng, G.-X., J. Org. Chem. 1992, 57,
5140.
10. Zlotsky, S. S.; Nazarov, M. N.; Kulak, L. G.; Rakhmankulov, D. L., J.
Prakt. Chem. 1992, 334, 441.
AlBr3, t-BuBr
50 60 °C, 1 h
11. Campaigne, E.; Heaton, B. G., Chem. Ind. (London) 1962, 96.
(9)
65%
12. (a) Hollywood, F.; Karim, A.; McKervey, M. A.; McSweeney, P., J.
Chem. Soc., Chem. Commun. 1978, 306. (b) Kafka, Z.; Vodicka, L.,
Collect. Czech. Chem. Commun. 1990, 55, 2043. (c) Williams, V. Z.,
Jr.; Schleyer, P. v. R.; Gleicher, G. J.; Rodewald, L. B., J. Am. Chem.
A facile rearrangement of Ä…-bromoethyldiethylborane (eq 10)
Soc. 1966, 88, 3862. (d) Nomura, M.; Schleyer, P. v. R.; Arz, A. A., J.
occurs when treated with Lewis acids.14 AlBr3 is very effective for
Am. Chem. Soc. 1967, 89, 3657. (e) Graham, W. D.; Schleyer, P. v. R.;
this conversion. AlCl3 or Silver(I) Tetrafluoroborate also give
Hagaman, E. W.; Wenkert, E., J. Am. Chem. Soc. 1973, 95, 5785.
high yields. The half-life for rearrangement is 0 5 min with these
(f) Gund, T. M.; Osawa, E.; Williams, V. Z., Jr.; Schleyer, P. v. R.,
catalysts. J. Org. Chem. 1974, 39, 2979. (g) Robinson, M. J. T.; Tarratt, H. J.
A list of General Abbreviations appears on the front Endpapers
ALUMINUM BROMIDE 3
F., Tetrahedron Lett. 1968, 5. (h) Gund, T. M.; Williams, V. Z., Jr.; 16. (a) Huisgen, R.; Ugi, I., Chem. Ber. 1960, 93, 2693. (b) Olah, G. A.;
Osawa, E.; Schleyer, P. v. R., Tetrahedron Lett. 1970, 3877. (i) Fort, Kobayashi, S.; Tashiro, M., J. Am. Chem. Soc. 1972, 94, 7448. (c)
R. C., Jr.; Schleyer, P. v. R., Chem. Rev. 1964, 64, 277. (j) Schleyer, P. v. Hausigk, D., Chem. Ber. 1970, 103, 659. (d) Dawson, I. M.; Gibson,
R.; Donaldson, M. M., J. Am. Chem. Soc. 1960, 82, 4645. J. L.; Hart, L. S.; Waddington, C. R., J. Chem. Soc., Perkin Trans. 2
1989, 2133. (e) Dewar, M. J. S.; Hart, L. S., Tetrahedron 1970, 26, 973.
13. Schneider, A.; Warren, R. W.; Janoski, E. J., J. Org. Chem. 1966, 31,
(f) Erre, C. H.; Roussel, C., Bull. Soc. Chem. Fr. Part 2 1984, 449.
1617.
14. Brown, H. C.; Yamamoto, Y., J. Chem. Soc., Chem. Commun. 1972, 71.
Melinda Gugelchuk
15. Meijer, H. J. D.; Pauzenga, U.; Jellinek, F., Recl. Trav. Chim. Pays-Bas
University of Waterloo, Waterloo, Ontario, Canada
1966, 85, 634.
Avoid Skin Contact with All Reagents