238. The chemistry of the pyrrocolines. Part III. Nitration

The Chemistry of the Pyrrocolines and the Octahydropyrrocolines.

“…VV Extension of this synthesis is exemplified by the preparation of -isonitrosophenacyl-a-picolinium chloride, from which 3-nitroso-2-phenylpyrrocoline arose in excellent yield (12). In contrast, the preparation of the corresponding quaternary nitro body from -nitrobromoacetophenone could not be effected (13). A further variant of this method was attempted with the replacement of apicoline by a-pyridyl-2-propanol and -pyridylacetone, using -bromoacetophenone as the halogenoketone (8).…”

“…It was also reported that the "white adduct" (XXIV) could be successfully converted to XIX by treatment with bromine in methanol or acetic acid. There is a report (13), however, that an attempt to repeat the direct preparation of XIX resulted only in the formation of XXIV.…”

“…Here, however, the reactive pyrrole ring is protected by the carboxylic ester groups. The successful oxidation of nitroso to nitro groups in the pyrrocoline nucleus has been effected under critical conditions with perhydrol (12,13). This agent, however, rapidly attacks the nucleus and is thus useful for degradative purposes (Section XIII).…”

“…The acyl groups are readily removed from these compounds by hydrolysis with mineral acids (11,19,20,81,83) and even boiling aqueous acetic acid is effective with 3-acetyl-2-phenylpyrrocoline (11). Diacyl derivatives appear to be somewhat more resistant than monoacyl derivatives (11) and those compounds containing a nitro (13,82) or nitroso (12) group in the nucleus cannot be hydrolyzed in this way. 3-Acetylpyrrocoline has been reported to be stable to boiling alcoholic potash (82) but heating 3-acetyl-2-phenylpyrrocoline in alcoholic solution in the presence of sodium ethoxide at high temperature and pressure removed the acetyl group (14).…”

“…Although Scholtz (82) prepared a nitroacetyl-and a dinitro-pyrrocoline by the action of nitric acid on 1,3-diacetylpyrrocoline, he stated that pyrrocoline itself could not be nitrated because of its sensitivity to oxidizing agents. However, work with 2-methyl-and 2-phenyl-pyrrocolines has recently shown (13) that it is possible to effect the direct nitration of this ring system for, while the action of nitric acid on these compounds at moderate temperatures caused mainly oxidation, rapid reaction at higher temperatures gave the 1,3-dinitro bodies in small yield in both instances. Furthermore, in concentrated sulfuric acid at low temperatures nitration was found to proceed readily with but little decomposition.…”