Organic Syntheses, Coll. Vol. 6, p.215 (1988); Vol. 50, p.13 (1970).
Iridium tetrachloride was originally obtained from Platinum Chemicals, Inc., Box 565, Asbury Park, New Jersey 07712, or from Alfa Products, Thiokol/Ventron Division, P.O. Box 299, 152 Andover St., Danvers, Massachusetts 01923
. More recently, the procedure has been repeated successfully with material obtained from Pfaltz and Bauer, Inc., a subsidiary of Aceto Chemical Co., Inc., 375 Fairfield Ave., Stamford, Connecticut 06902.
The order of mixing the catalyst components is required for good results, and the sequence described should be followed. Particular care should be taken not
to add the trimethyl phosphite
before the water, as the reaction between it and concentrated hydrochloric acid
is extremely violent.
The reaction solution is often dark-colored at the beginning but lightens as reflux continues. The reflux time may be varied with the amount of ketone to be reduced. The completeness of the reaction may be followed by removing small aliquots, working up these samples as described in the text, and analyzing the product mixture by GC (see (Note 6)
catalyst used in this preparation may be regenerated by reducing the volume of the aqueous residue to about 200 ml. at diminished pressure. This solution is then used instead of the iridium tetrachloride
and water called for in the procedure.
The product was analyzed by GC using a 9-ft. 20% Carbowax 20M on 45/60 Chromosorb W column at 150°. The order of increasing retention times is: ketone, cis
Recrystallization is best accomplished by dissolving the crude product in hot ethanol (approx. 35 ml. per 10 g.)
followed by adding water (approx. 25 ml. per 10g.) and allowing the solution to cool slowly to 0°. The fluffy white needles are filtered using a sintered-glass funnel
and dried over P2O5
at atmospheric pressure. Recooling the filtrate affords a second crop of product, for an overall yield of 75–87%
procedure employs a readily available starting material and produces essentially pure cis
isomer in good yield. In view of the fact that the catalyst may be reused several times with little loss in stereoselectivity, the expense of the iridium tetrachloride
is not a serious impediment.
Since this preparation was submitted, a number of reductions of 4-tert-butylcyclohexanone
to the cis
alcohol, with 93–100% selectivity, using various bulky, complex metal hydrides have been described: lithium tri-sec-butylborohydride (L-Selectride)
,12,13 lithium trisiamylborohydride
,13,14,15 lithium tri-trans-2-methylcyclopentylborohydride
,14 lithium dimesitylborohydride
,16 lithium 2,6-di-tert-butylphenoxyneopentoxyaluminumhydride
high (94–99%) selectivity is also attained by catalytic hydrogenation with various rhodium
Hydrogenation over rhodium-on-carbon18
) followed by purification with liquid chromatography appears to be an attractive method, one which avoids the need for special reagents.
Chemical Abstracts Nomenclature (Collective Index Number);
potassium carbonate (584-08-7)
hydrochloric acid (7647-01-0)
acetic acid (64-19-7)
diethyl ether (60-29-7)
magnesium sulfate (7487-88-9)
trimethyl phosphite (121-45-9)
iridium tetrachloride (10025-97-5)
Cyclohexanol, 4-(1,1-dimethylethyl)-, cis- (937-05-3)
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