2
460
M. P. Pollastri et al. / Tetrahedron Letters 42 (2001) 2459–2460
Table 3. Substrate versatility. Yields shown are isolated, with the exception of the entries denoted with *, which were
determined using GC/MS
provide the lowest solubility of the oxidized byproduct
while still promoting the desired conversion. We under-
took a relative solubility study by integrating LC/MS
chromatograms, and several solvents which resulted in
hexachloroethane (3.68 mmol, 1 equiv.) was dissolved
in 11 mL THF and 0.73 g diphos (1.84 mmol, 0.5
equiv.) was added. The reaction was allowed to stir at
room temperature for 3 hours, at which time the sus-
pension was filtered through Celite, the filtrate evapo-
rated, and the resulting residue was purified by hexane
elution through a short pad of silica gel. Evaporation
provided 3-chloro-1-phenylbutane in 64% yield. As
low solubility of diphos–O were identified (Table 1).
2
The utility of these solvents for the alcohol–halide
conversion was then evaluated.
The results shown in Table 2 indicate that diphos can
readily facilitate the desired conversion. Using methyl-
ene chloride as the solvent, >95% conversion was
achieved. However, the desired precipitation of the
shown in entry 5 (Table 2) 75% of the diphos–O was
removed by filtration, and the remaining oxide was
retained on the silica gel.
2
diphos–O was not observed (entry 1). Using the signifi-
We have described an alternative method for conver-
sion of alcohols to halides using diphos, which is con-
verted to a readily-filtered dioxide byproduct. The
reaction provides a good alternative to the standard
triphenylphosphine–carbontetrahalide conversion, as
well as to the polymer supported phosphine reagents.
2
cantly less polar CCl resulted in precipitation of the
4
byproduct but conversion was poor (entry 2). Near
quantitative removal of diphos–O2 by filtration was
achieved when using toluene as the solvent (entry 3).
However, alcohol–halide conversion was incomplete
despite addition of excess hexachloroethane. Higher
conversion can be achieved using a higher concentra-
tion of diphos. Unfortunately, the resulting residue was
not readily removed by filtration (entry 4). The balance
of high conversion and readily filterable byproduct was
achieved when using THF as the solvent (entry 5).
References
1. Larock, R. C. Comprehensive Organic Transformations;
VCH: New York, 1989; pp. 353–360.
2. Appel, R. Angew Chem., Int. Ed. Engl. 1975, 14, 801.
Table 3 lists the various alcohol substrates which were
examined for transformation to the corresponding chlo-
rides and bromides. In a representative reaction, 0.5 g
3. Harrison, C. R.; Hodge, P.; Hunt, B. J.; Khoshdel, E.;
Richardson, G. J. Org. Chem. 1983, 48, 3721.
4. O’Neil, I. A.; Thompson, S.; Murray, C. L.; Kalindjian, S.
B. Tetrahedron Lett. 1998, 39, 7787.
4-phenyl-2-butanol (3.68 mmol, 1 equiv.) and 0.87 g
.
.