Chasmanine

Allenes behave as somehow special olefins in such photocycloadditions 476a,b,477) Additions of enones to allene have been used as key step in the synthesis of the alkaloids annotinine 478a) (4.65) and chasmanine (4.66) 478b). 

The full paper has appeared on a synthesis of steviol. The route was based on the stereocontrolled photoaddition of allene to the cyclopentene-1-aldehyde (178), reduction of the aldehyde, and then solvolysis of the methanesulphonate (179). Papers on the synthesis of the aromatic ether (180) and on the construction of the c/d ring system of the alkaloid chasmanine " have been published. 

Treatment of the ketone (705) with methanolic KOH led to hydrolysis of the acetate group, retro-aldol reaction and aldol cyclization, which eventually afforded a mixture of epimeric alcohols (106)33). This strategy was used to construct the basic skeletons of various alkaloids, e.g. talatisamine 34), atisine 35) and chasmanine 36). 

An Improved Synthesis of 13-Desoxydelphonine and Chasmanine.—Wiesner and co-workers40,41 have reported a more efficient synthesis of (102). This intermediate (102) has been used in the synthesis of 13-desoxydelphonine (103)... 

Five new diterpenoid alkaloids have been isolated from Aconitum species (Ranunculaceae) and five from Delphinium species (Ranunculaceae). Four new Anopterus (Escalloniaceae) bases have been identified. The most significant synthetic achievement has been the total synthesis of racemic chasmanine. A detailed review of the alkaloids of Delphinium staphisagria has appeared.1... 

Structure and Absolute Configuration of Chasmanine 14 -Benzoate Hydrochloride.—The full report on the X-ray crystallographic structure determination of this derivative of chasmanine, isolated from the roots of Aconitum chasmanthum Stapf, has appeared9 (cf. Vol. 7, p. 253). The structure was computed to be (1) by direct methods. The absolute configuration as determined by the R-ratio test is IS, 4S, 5R, 6R, 1R, 8S, 9R, 1 OR, 11S, 13R, 14S, 16S, 17R.10 This structure determination confirmed the structures of chasmanine (2) and homochasmanine (3) that had previously been proposed on the basis of chemical and spectral data.11... 

Total Synthesis of Chasmanine.—Wiesner and his co-workers38,39 have accomplished a landmark in diterpenoid alkaloid chemistry in their completion of the total synthesis of racemic chasmanine (49), a hexacyclic base with six oxygen functionalities. The synthesis of the intermediate (50) was reviewed in the previous Report (Vol. 7, pp. 257—259). 

The reactions by which (50) is converted into chasmanine were studied in model systems.38 An earlier scheme40 (cf. Vol. 7, p. 258) was found to be unsatisfactory due to the unfavourable equilibrium between (51) and (52). The next model... 

Unlike the model system, (66) could not be brominated directly. Therefore, it was converted into the ketone (67) by heating in 80% acetic acid, and this ketone was brominated with excess bromine in ether to give (68). Conversion of (68) into the acetal (69) was accomplished with diethylene orthocarbonate and toluene-p-sulphonic acid. Rearrangement of (69) to (70) was effected by heating with excess 1,5-diazabicyclo[3,4,0]nonene in xylene-DMSO. On comparison of i.r., n.m.r., and mass spectral data, this synthetic racemate was identical with the corresponding derivative from natural chasmanine. 

Oxymercuration of (70) gave (71), which was then heated in 80% acetic acid to give 14-dehydro-a-oxochasmanine (72). Reduction of (72) with lithium aluminium hydride gave racemic chasmanine - identical with the natural material by t.l.c., i.r., n.m.r., and mass spectral analyses. 

Alkaloids of Aconitum forestii Stapf.—Wei-Shin Chen and Breitmaier23 have reported the isolation and elucidation of the structure of a new alkaloid from plants of A. forestii Stapf var. albo-villosum collected in the Yun-nan Province of China. Foresaconitine (C35H49N09 m.pt 153—154 °C) was the major alkaloid (0.2%) isolated from the roots. The alkaline hydrolysis of foresaconitine afforded chasmanine (59). From this transformation and from comparisons of H and 13C n.m.r. spectra, structure (60) was assigned to foresaconitine. This alkaloid is identical with villmorrianine C, which is described on page 264. 

Alkaloids of Aconitum yesoense Nakai.—Sakai and co-workers42 have reported the isolation and elucidation of the structure of three new C19 diterpenoid alkaloids from Aconitum yesoense Nakai. These minor bases, ezochasmanine, ezo-chasmaconitine, and anisoezochasmaconitine, were isolated together with pseudo-kobusine (92), chasmanine (59), and jesaconitine (93). Ezochasmanine (94) (C25H41N07 m.pt 115—118 °C) formed a mixture of the monoacetate (95) and the diacetate (96) when treated with acetic anhydride in pyridine. The reaction of... 

Further synthetic studies of diterpene alkaloids with the aziridine rearrangement as a key reaction have been reported and led to the synthesis of diterpene alkaloids chasmanine (234) and 13-deoxydelphonine (235). 

The problem of the incorrect assignment of the structure of chasmanine based on the chasmanine-browniine-lycoctonine correlations (cf. vol. 6) was examined in view of these n.m.r. data. Complete assignments for all of the resonances for lycoctonine (56a) and browniine (56b) and their corresponding acetates were made. These data indicated that lycoctonine and browniine had identical stereochemistry in ring A, as have neoline and chasmanine. The reactions of the attempted browniine-chasmanine correlation would hot be expected to affect the oxygen function at C-1 it was therefore concluded that this work must be in error. 

Syntheses Directed Toward Chasmanine.—Outstanding progress toward the total synthesis of the complex hexacyclic diterpenoid alkaloid chasmanine (46) has been reported. The pentacyclic intermediate (69) has been prepared, and, using a model system, the methodology for the conversion of this compound into chasmanine has been developed. These experiments employed many processes developed in the earlier synthetic work, and in a number of instances, considerable improvements in the methods have been made. 

Diterpenoid Alkaloids.— The alkaloids of Delphinium staphisagria include some bisditerpenoid alkaloids such as staphidine, staphinine, and staphimine. The full paper has appeared on the structure and stereochemistry of delphisine, neoline, chasmanine, and homochasmanine. The application of n.m.r. measurements to these alkaloids has led to the revision of the structure of the alkaloid A from D. bicolor... 

A total synthesis of the C19 alkaloid chasmanine (7) has been described it represents a landmark in diterpene alkaloid chemistry (K. Wiesner and co-workers, Canad. J. Chem., 1975, 2140 1976, 54, 1039 1977, 1091 Heterocycles, 1977,... 

The conversion of (51) into chasmanine (7), again based on a number of reactions applied to model compounds, is summarised in Scheme 2. 

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