Weygand/Hilgetag Preparative Organic Chemistry

Formation of the carbon-deuterium bond by addition 89
metal catalysts are therefore reduced with deuterium or are saturated therewith
by being stirred for a considerable time (30-60 min) in an aprotic solvent
under an atmosphere of deuterium; Khan 20 ' 21 gives a detailed prescription for
the preparation of suitable Raney nickel catalysts, wherein, after decomposition
of the alloy, dioxan is used as wash fluid in place of ethanol, a considerable
part of the hydrogen dissolved in the nickel is removed by repeated partial
distillation of pure dioxan, and the residual hydrogen is exchanged for deuterium
by suspension of the catalyst in D2O under a deuterium atmosphere.
Since a rapid exchange sets in on the catalyst between gaseous deuterium and
the hydrogen of solvents that yield protons, dioxan, cyclohexane, and ethyl
acetate are favored as solvents for deuteration. If it is essential to use alcohol
or acetic acid, the hydrogen of the hydroxyl group must be previously exchanged
for deuterium. Similarly it is advisable to replace labile hydrogen atoms
by a protecting group before deuteration of the compound.
Catalytic hydrogenation of carbon-carbon multiple bonds would be an
excellent method of preparing compounds labeled by deuterium at pre-determined
positions were it not that unfortunately migration of the double bond
and uncontrollable H -» D exchange on the catalyst surface limits its applicability.
Even under mild conditions a part of the deuterium introduced appears
at other positions. 22 * 23 Relatively good results are obtained with the nickel
catalysts mentioned above.
Catalytic deuteration of carbon-carbon multiple bonds is thus preferably
restricted to small uncomplicated molecules or, as in the formation of [D2]dihydrouracil
from uracil, 24 to such as contain a limited number of C-H bonds.
Good results can also always be obtained when the substance to be reduced
does not contain hydrogen in the allyl position, e.g., withZl 1 -3-keto steroids, 25
and in partial reduction of carbon-carbon triple bonds. Khan 20 gives the
following description of the last-mentioned reaction:
[9,10-D2l-9-Octadecene: A solution of 9-octadecyne (5 g) in purified dioxan (125 ml) is
deuterated in the presence of pretreated Raney nickel. The very selective reaction ceases after
absorption of one equivalent of deuterium. The catalyst is then filtered off, the solution is
evaporated, and the crude residue is dissolved in sufficient ether to give an approximately
10% solution. After cooling to ca. —45° for 2 h, the resulting crystals are removed; further
cooling to ca. —50° gives a second fraction. On distillation of the two fractions at 2-3 mm
the product of m.p. 140-142° is obtained.
Chemical methods are less often used for saturation of C=C bonds. Recently,
however, dideuteriodiimine seems to have established a firm position
for this reaction, 26 whereby ds-saturation of the carbon-carbon double bond
results. Another, interesting reaction of the carbon-carbon double bond is that
with B2D6, whose end result is an