Indoloquinolizidine synthesis : Stereochemistry and mechanism of cyclisation

A stereocontrolled cyclisation of suitably substituted indole derivatives can be explained by the revised Pictet-Spengler reaction mechanism.     

Syntheses of (±)-17α- and (±)-17β-hydroxytacamonine; determination of configuration at C-17

Both (±)-17α-hydroxytacamonine (3) and its 17β-isomer (4) were synthesized in two steps (one-pot) from aldehyde mixture 5/6 via the cyanohydrin reaction. NMR spectral characterization of isomer 3 revealed it to be unidentical with natural 17-hydroxytacamonine, whereas spectral data of isomer 4 were in agreement with those published for the natural isomer. The configuration at C-17 was confirmed by NOE difference spectroscopy.     

Massenspektren neuer Phloroglucide,insbesondere solcher mit Valerylseitenketten

Mass spectra of phloroglucinol derivatives recently isolated from African Dryopteris species are presented. Phloroglucides with n-valeryl side chain were found in these ferns for the first time. In the mass spectra they show strong peaks corresponding to loss of propene (C₃H₆) produced by McLafferty rearrangement, as shown in model compounds. Aside of the rottleron change (discussed formerly) this must be considered in order to avoid wrong interpretation, particularly when mass spectra are used to analyse mixtures of homologues, as usually present in the plants. If valeryl side chains are present other methods must be used therefore to measure the amount or show the absence of lower homologues with acetyl side chains.     

Aldehyde Intermediates in the Synthesis of Tacamine-Type Indole Alkaloids: Preparation of (±)-apotacamine

The synthesis of aldehyde intermediates suitable for the preparation of indole alkaloids of the tacamine ( 1 ) type is described. The four possible aldehydes 4–7 were prepared from methyl 5-ethylnicotinate ( 8 ) in a few simple steps using a base-catalyzed epimerization as the final step (Schemes 1 and 2). The key aldehyde 4 , which is an analogue of the important vincamine intermediate 3 (‘Oppolzer's aldehyde’), was finally converted into the indole alkaloid (±)-apotacamine ( 21 ).     

Synthetic studies in the alkaloid field—V: Determination of the stereochemistry of several l,2,3,4,6,7,12,12b-octahydro-3-methoxycarbonylindolo-[2,3-a]quinolizine derivatives by 13C NMR spectral analysis

The C(12b)-C(2)-C(3) stereochemical relationship in several racemic 1,2,3,4,6,7,12,12b-octahydro-3-methoxycarbonylindolo [2,3-a]quinolizine derivatives has been determined by ¹³C NMR spectral analysis. The proper shift assignment was confirmed by recording the spectra of selectively deuterated derivatives. The shifts of specific carbons are found to be conformationally diagnostic. The C(12b)-C(2)-C(3) stereochemical relationship in indolo[2,3-a]quinolizines obtained by selective alkaline decarboalkoxylative cyclization of partially hydrogenated 1-[2-(3-indolyl)ethyl]3,5-dimethoxycarbonylpyridine derivatives is discussed.     

The specific heat of Sm metal between 0.45 and 6 K

The heat capacity of an isotopically enriched (98.3%) ₆₂¹⁵²Sm metal specimen has been measured. Because the nuclear contribution to C_p is absent in an even-even isotope, the electronic specific heat, C_E = 13.5 T mJ/mole·K², could be determined with higher accuracy (± 2%) than before.