Nisentil ,Roche ,US ,1949
In a round-bottom flask provided with stirrer, dropping funnel, condenser and
a gas outlet for keeping the system under nitrogen, 200 cc of dry ether is
placed and 4.6 grams of lithium cut into thin strips is added. 52 grams of
bromobenzene in 50 cc of dry ether are added dropwise and after addition,
the mixture is refluxed for 2 hours. This procedure results in the formation of
phenyl-lithium. Other aryl-lithium compounds can be prepared in a similar
manner by reacting lithium metal or a lithium compound capable of
transferring lithium and a compound having an exchangeable halogen group
as, for example, bromonaphthalene.
The solution of phenyl-lithium is cooled to -20°C and to this a solution of 12.7
grams of 1,3-dimethyl-4-piperidone, prepared according to the method of
Howton, J. Org. Chem. 10, 277 (1945), in ether is added dropwise with
stirring. After the addition, the stirring is continued for a further 2 hours at -
20°C. The lithium complex, 1,3-dimethyl-4-phenyl-4-oxylithium piperidine,
which forms is soluble in the ether and can be recovered there from. To
prepare the piperidinol, the lithium complex, while in the reaction mixture is
decomposed by the addition of an ice and hydrochloric acid mixture. The
acidified layer is separated, basified and extracted with ether. After drying the
ether solution and removing the solvent, the residue on distillation in vacuum
distills chiefly at 155°C/10 mm, yielding the product, 1,3-dimethyl-4-phenyl-
4-hydroxypiperidine, which, on crystallization from n-hexane melts at 102°C.
On treatment with propionic anhydride catalyzed with a trace of sulfuric acid,1,3-dimethyl-4-propionoxy-4-phenylpiperidine is attained. The latter
compound can be converted into the hydrochloride salt by reaction with
hydrogen chloride. This salt after crystallization from acetone has a melting
point of 209°C.
