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Enmein

In the course of the total synthesis of enmein, Fujita and co-workers (7) have discovered that the intramolecular cyclization of the enolate 23 of the corresponding tetracyclic keto-aldehyde at room temperature gave only ketol 24. However, when the same reaction is conducted at 60°C, thermodynamically controlled conditions prevail, and the epimeric product 25 is obtained. Inspection of molecular models indicates that the kinetically controlled product 24 is again the result of an anti peri planar arrangement of the enolate and the aldehyde double-bonds. Also, as in the previous examples, the isomer 25 comes from a synclinal arrangement of the reacting functional groups. [Pg.355]

During the chemical interconversion of gibberelin-A 5 and enmein, Somei and Okamoto (181) investigated a nitrone photolysis reaction which gave the veatchine-type compound 381. [Pg.186]

Enmein was converted to 20-hydroxykaur-6-en-15a-pyranylether (382), which was oxidized with chromium trioxide in pyridine to afford the aldehyde 383. The latter was converted with hydroxylamine to the oxime 384. The nitrone 385 was prepared by treatment of 384 with bromine azide. Photolysis of 385 gave the desired compound 381 in 46% yield. This intermediate possesses several useful functionalities (e.g., carbinolamine ether linkage), which may be of interest for synthesis of C20-diterpenoid alkaloids after minor changes in this scheme. [Pg.186]

The partial synthesis from epicandicandiol of some C- and H-labelled kaurene derivatives has been described.These have possible application in the study of the biosynthesis of the Isodon diterpenoids. The syntheses of [17- C]kaur-16-en-20-ol from enmein and of 3-oxygenated derivatives of [17- C]kaur-16-ene from ent-3jS,19-dihydroxy-kaur-16-ene have also been described. The synthesis of radioactive aphidicolin has also been reported. It has been shown ° that ent-kaur-15-ene is formed by the dwarf mutant (ds) of maize in place of ent-kaur-16-ene. [Pg.119]

During a total synthesis of the diterpenoid enmein, the tricyclic alcohols (47) and (48) were converted into a range of c-ring ketones (Scheme 5). The degree of reduction and the ease with which it occurs, relative to (23), make it apparent that intramolecular protonation is involved here also. ... [Pg.496]

Fujita and co-workers have converted the diterpenes trichokaurin (88) and enmein (89) into the keto-carboxylic acid (90), which had earlier been transformed into atisine and veatchine. The 1-mesylate of trichokaurin was oxidised to the... [Pg.362]

Enmein (89) had previously been converted into the unsaturated lactone-ester (94). Acyloin cyclisation of this gave the desired hemiketal (95 R = H) in 50% yield. Photo-oxidation of its monoacetate (95 R = Ac) gave the allylic alcohol... [Pg.362]

Synthesis of a Veatchine-type Intermediate.—A recent synthesis32 of gibberellin-A15 involves an intermediate of interest for the synthesis of diterpene alkaloids. Enmein (58) had previously been converted to the alcohol (59).33 Oxidation of this alcohol afforded an aldehyde which was converted to its oxime. Removal of the blocking group afforded (60). The nitrone (61), prepared by treatment of (60) with bromonium azide, was photolysed to (62). The resemblance of this intermediate to several alkaloids of the veatchine-type is obvious. Minor variations of this scheme may prove to be of synthetic interest. [Pg.258]

R. lophanthoides lothanthoidin A(I303) lothanthoidin C(I402) lothanthoidin E(I403) enmein(1)... [Pg.173]

Details of the conversion of enmein into ( — )-kaurene have been described. The hemi-acetal (67), produced by an acyloin condensation of enmein derivatives,... [Pg.176]

The first investigation of the bitter principles in enmei-so was carried out in 1910 and isolation of a crystalline bitter substance was reported by Yagi (2). In 1954, antibacterial activity was reported for the extract (5). In 1958, isolation of enmein, one of the major diterpenoid constituents, initiated structure determination and investigation of other constituents. Since then, our knowledge of the diterpenoids of Rabdosia species has developed to a remarkable degree. Particular interest has centered on their antitumor activity. For previous reviews of the chemistry of Rabdosia diterpenoids, the reader is referred to Ref. (4—7). [Pg.78]

The chemical investigation of Rabdosia plants began with isolation of the bitter principles of enmei-so (R, japonica and R. trichocarpa). During the first period (1958—1966), the main effort was devoted to the structure elucidation of enmein, one of the major constituents. After this was... [Pg.78]


See other pages where Enmein is mentioned: [Pg.136]    [Pg.189]    [Pg.411]    [Pg.142]    [Pg.143]    [Pg.144]    [Pg.147]    [Pg.119]    [Pg.142]    [Pg.143]    [Pg.1001]    [Pg.111]    [Pg.174]    [Pg.177]    [Pg.101]    [Pg.208]    [Pg.77]    [Pg.77]    [Pg.77]    [Pg.77]    [Pg.77]    [Pg.77]    [Pg.77]    [Pg.77]    [Pg.79]   
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Enmein 3-acetate

Enmein derivatives

Enmein into Gibberellins

Enmein synthesis

Enmein type diterpenoids

Enmein via Birch reduction

Rabdosia japonica [Enmein

Structure Determination of Enmein in Outline

Total Synthesis of Enmein

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