No abstract

In the course of the isolation of reserpine from the tertiary alkaloids of Alstonia constricta root bark, a number of other alkaloids were obtained, and these alkaloids have now been the subject of further study. Alstonidine, a previously known alkaloid for which the provisional structure (6) was suggested, has now been shown to have the stereochemistry depicted in (7a). A new alkaloid, alstonilidine, has been shown to be (8). Vincamajine (9) has been identified, and two new alkaloids, O-3,4,5-trimethoxycinnamoylvincamajine (10) and 0-3,4,5-trimethoxybenzoylquebrachidine (11) have been isolated from the "reserpine concentrate". Another alkaloid, probably C43H50N4O7, appears to be a new member of the "bisindole" group.

The compound 2,2,4,4,6-pentamethyltetrahydropyrimidine hydrate, formed in the reaction between acetone and ammonia at room temperature: is converted by nitrous acid to the 5-oximino derivative in 30 per cent. yield. This oxime is decomposed by acid under mild conditions to give acetone, ammonia, and the salt of 4-amino-4-methyl- 2,3-pentanedione 3-oxime. More vigorous acid treatment of the cyclic oxime, or reaction of the open-chain 3-oxime with boiling dilute acid, causes a migration of the oximino group to the 2 position. Evidence is adduced to show that the 2-oxinze has the α- (anti) configuration, whereas the 3-oxime has the β- (syn) configuration.

Three 2,4-dienals, 2,4-heptadienel, 2,4-nonadienal, and 2,4-hendecadienal, have been prepared synthetically for the first time, their semicarbazones, 2,4-dinitrophenylhydrazones and tetrahydroimidazole derivatives described, and ultraviolet absorption characteristics of the aldehydes and the two first-named derivatives recorded. The infra-red spectrum of 2,4-heptadienal is recorded and evidence presented for an all-trans-configuration.

The preparation of 2,2,4,6-tetramethyldihydropyridine by the reaction of acetone and ammonia at temperatures of 100-180 �C. has been studied; using an alkaline catalyst at 120 �C. for 3 hr, a yield of over 60 per cent. can be obtained. This dihydro-pyridine is identical with the product obtained by Matter (1948) in the pyrolysis of 2,2,4,4,6-pentamethyltetrahydropyrimidine Possible mechanisms for its formation are discussed. Catalytic hydrogenation over Raney nickel leads to tetramethyl-piperidine, while with palladium a partial reduction product, formulated as 2,2,4,6-tetramethyl-2,3,4,5-tetrahydropyridine is obtained ; the chemistry of these reduction products has been examined.