64 J. CHEM. RESEARCH (S), 1997
J. Chem. Research (S),
1997, 64–65†
A Facile Synthesis of Ketones from Organoboranes using
Pyridinium Fluorochromate†
Edward J. Parish,* Stephen A. Kizito and Hang Sun
Department of Chemistry, Auburn University, Auburn, AL 36849-5312, USA
Pyridinium fluorochromate (PFC), in refluxing methylene dichloride, has been found to be an effective and convenient
reagent for the oxidation of organoboranes to the corresponding ketones in good yield.
Table 1 Hydroborationa of olefins and oxidation of the resulting
Oxidation of organoboranes with aqueous chromic acid is
standard methodology for the synthesis of ketones.1–5 The
use of diethyl ether, as the reaction solvent, was found to be
an improvement in procedure and resulted in higher
yields.2,6,7 More recently, pyridinium chlorochromate (PCC)
has been used for the oxidation of organoboranes to the
corresponding ketones8–10 and aldehydes.8 In the present
study, we have developed a useful modification of this reac-
tion, using pyridinium fluorochromate (PFC) in a non-
aqueous reaction medium. Using PFC in refluxing methylene
dichloride, we were able to achieve the conversion of organo-
boranes into the corresponding ketones in good yield.
The direct synthesis of ketones from organoboranes (pro-
duced from the hydroboration of olefins) represents a major
transformation in organic chemistry. Improvements and
modification in these methods can facilitate the chemical
synthesis of these compounds.
organoboranes to ketones by pyridinium fluorochromate (PFC)b
Olefin substrate
Ketone product(s)
% Yieldc
78
77
76
81
In the present study, we have utilized the techniques of
hydroboration to form organoboranes in high yields.12,13
The hydroboration of several olefins was conducted using
74 and 9
.
borane–tetrahydrofuran complex (NH3 THF). As expected,
hydroboration of substrates 3, 5, 9 and 12 proceeded via anti-
Markovnikov cis addition.11,12 In substrate 9, cis addition from
the less hindered side of the double bond gave 10 as the
major product.13 We have found that the C-24 double bond of
86
.
lanosterol acetate (12) selectively reacts with BH3 THF to
aReactions were conducted at 2 °C in THF using BH3·THF. bThe
reactions were carried out in refluxing methylene dichloride.
cYield of isolated ketone product.
yield the C-24 organoborane. Oxidation of these resulting
organoborane intermediates by PFC in refluxing methylene
dichloride gave the ketones shown in Table 1.
Pyridinium fluorochromate (PFC) is a mild and selective
oxidant and has been used in the oxidation of a number of
organic compounds.14,16 Representative ketones have been
ene dichloride (100 ml). PFC (15 g) and molecular sieves (100 mg;
type 4A) were added and the reaction mixture was refluxed for 3 h.
Saturated aqueous NaCl was added and the mixture thoroughly
extracted with methylene dichloride. The solvent was removed at
reduced pressure. Products 2, 4 and 6 were purified by distillation,
while products 8, 10, 11 and 13 were purified by column chroma-
tography (using a solvent gradient of diethyl ether in toluene) to
give the yields presented in Table 1. The procedures used for
column and thin layer chromatography (TLC) have been described
previously.17 The purified products 10, 11 and 13 were recrystal-
lized from acetone–water. All isolated reaction products were
compared with authentic compounds9,10 and were confirmed by
.
prepared from alkenes via hydroboration with BH3 THF in
order to demonstrate the generality of the oxidation of
organoboranes with PFC. The high yields, anhydrous reac-
tion conditions and easy work-up procedure make this a
highly convenient method for the direct conversion of
alkenes into ketones.
In summary, the reactions reported herein expand the
scope and utility of synthetic transformations known to be
accomplished by PFC and offer an alternative method for the
synthesis of ketones from organoboranes.
1
bnp or mp, IR, MS, H and 13C NMR, and TLC.
Experimental
Received, 19th August 1996; Accepted, 5th November 1996
Paper E/6/05752G
Hydroboration–Oxidation: General Procedure.sThe olefins
shown in Table 1 (9.5 mmol) were each dissolved in THF (75 ml)
and cooled to 2 °C in an ice–water bath. While maintaining a
.
BH3 THF solution (10 ml, 10 mmol)
nitrogen atmosphere a 1
M
References
was added over a 10 min period. The reaction mixture was stirred
for 1 h at 2 °C under nitrogen. Ice was then cautiously added to
decompose the excess hydride, water was added, and the reaction
mixture thoroughly extracted with diethyl ether. The extracts were
dried over anhydrous MgSO4 and evaporated at reduced pressure,
toluene was added and the solvent evaporated at reduced pressure
to remove traces of water (azeotrope). The residue was dried in a
vacuum desiccator over P2O5 for 2 h and then dissolved in methyl-
1 H. C. Brown and C. P. Gary, Tetrahedron, 1985, 42, ???.
2 H. C. Brown and C. P. Gary, J. Am. Chem. Soc., 1961, 83,
2951.
3 R. Pappo, J. Am. Chem. Soc., 1959, 81, 1010.
4 R. Pappo, L. F. Fieser and M. Fieser, in Steroids, Reinhold, New
York, 1959, p. 684.
5 H. C. Brown, Rothberg and D. L. Vander Jagt, J. Org. Chem.,
1972, 37, 4098.
*To receive any correspondence.
6 H. C. Brown and C. P. Gary, J. Am. Chem. Soc., 1961, 83,
†This is a Short Paper as defined in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1997, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).
2952.
7 H. C. Brown, C. P. Gary and K.-T. Liu, J. Org. Chem., 1971, 36,
387.
Parish, Edward J.
