Elaeocarpus alkaloids synthesis

This strategy is successfully applied to the synthesis of the indolizidine framework of an Elaeocarpus alkaloid, (-)-elaeokanine C (Eq. 5) [15,16]. Fur-... 

Nitrone cycloadditions may also lead to pyrrolidine according to another type of cycloaddition. The power of the method is illustrated by the synthesis of the peripentadenine intermediate 133 en route to Elaeocarpus alkaloids (Scheme 37) (185). 

A synthetic route to Elaeocarpus alkaloids has been explored. Acylation of the lithium enolate (197) by the benzoyl cyanide (198) gave the diketone (199), which is the key intermediate in a previously reported synthesis of elaeocarpine (Section 3.08.8.2) (79TL1339). 

The use of nitrones in alkaloid synthesis has now been extended to both aromatic and non-aromatic Elaeocarpus alkaloids.5-7 The reaction sequence shown in Scheme 1 gives ( )-elaeocarpine (10) and ( )-isoelaeocarpine (11), and... 

An alternative and successful approach to the Elaeocarpus alkaloids has been based on use of the vinylogous urethane (20). This method has led to the synthesis of ( )-elaeocarpine, ( )-isoelaeocarpine, and the ( )-elaeokanines A, B, and C.8 The vinylogous urethane method has been extended to the synthesis of ipalbidine, which is the aglycon of the alkaloid ipalbine.9... 

The ester (3) has been shown to be a useful starting point for the synthesis of Elaeocarpus alkaloids. Ester (3) is converted by several steps into the protected keto-aldehyde (4) this, by reaction with n-propylmagnesium bromide followed by a Jones oxidation of the product and then deprotection, gives the diketone (5). As... 

Aldol cyclization. Exposure of the hydroxy ketone 1 to excess potassium t-butoxide and benzophenone in refluxing benzene provides the o,/S-unsaturated ketone 2 directly/ This transformation involves a modified Oppenauer oxidation followed by aldol closure of the resulting keto aldehyde. The product serves as an intermediate in the synthesis of Elaeocarpus alkaloids. 

The theimolysis of 2-substituted 2,5-dihydrothiophene 1,1-dioxides leads to ( ) conjugated dienes via cycloieversion followed by the concerted cheletropic extrusion of sulfur dioxide. The thermolysis of the a, -alkylated sulfone (96) gives the intennediate, which loses SO2 to give 1-dodecadien-l-yl acetate (98), a component of the sex pheromone of the red bollwoim moth. Tliis procediue has been extended to the thermolysis of a,3-dialkylated sulfones in order to obtain ( , )-1,4-disubstituted-1,3-dienes (equation 46). Similar processes have been used for the syntheses of alkaloids. The synthesis of an Elaeocarpus alkaloid, elaeokwine A (100), makes use of the retrodiene extrusion of sulfur dioxide to give the 1,3-diene intermediate (99) that is subsequently consumed by an intramolecular imino DA reaction (equation 47). o-Xylylene (102) has been generated by rDA expulsion of SO2 from benzo-fiised 3,6-dihy(ho-l,2-oxathiin 2-oxide (101). ... 

The synthesis of ipalbidine (125), the aglycon of ipalbine, was based on a related approach. The vi-nylogous carbamate (123) was prepared from the V-alkylated thiobutyrolactam (122) via an analogous sulfide-contraction process as described above (Scheme 26). The bicyclic intermediate (124) was generated by selective hydrolysis of the saturated ester followed by immediate treatment with methyl chloro-formate in the presence of catalytic tetrabutylammonium iodide. The bicyclic compound (124) was further elaborate to racemic ipalbidine (125). Parallel applications of this strategy were employed to prepare a series of Elaeocarpus alkaloids (126), (127) and (128) (Scheme 27) as well a benzomorphan analog (129 Scheme 28). °... 

In an alternative approach to the nitrone method for the synthesis of Elaeocarpus alkaloids (cf. vol.ll, p.61), a 1,3 dipolar cycloaddition of 1-pyrroline 1-oxlde to a substituted enone gives the isoxazolidine (2), which was converted in a number of steps into the compound (3), the C-7 epimer of elaeokanine C. Oxidation of the epimer (3) afforded the diketone (4), an intermediate in a previously published synthesis of ( )-elaeokanlne C. 

The synthesis of indolizidine alkaloids, including tylophorine and 6-coniceine as well as Elaeocarpus alkaloids, by the intramolecular imino Diels-Alder method (cf. vol.12, p.71) has been pub-... 

Enaminones 258, prepared by the Eschemoser method (Section II,B), were converted by different procedures to the indolizidines 259, 260, and 261, Scheme 70 (80JOC1713, 80TL1373). These indolizidines are potential precursors of the Elaeocarpus alkaloids and 259 (R = P-CH3OC6H4) eventually led to the synthesis of Ipalbidine (80JOC1713). 

Simple indolizidine alkaloids from the genus Elaeocarpus were surveyed in Volumes 28 and 44 of this treatise (1,2). The latter survey highlighted a communication on the synthesis of (+ )-elaeokanines A (307) and C (308) by Koizumi and co-workers (289) that has since been published with full experimental details (290). 

Herbert, R. B., The synthesis of indolizidine and quinolizidine alkaloids of Tylophora, Cryptocarya, Ipomoea, Elaeocarpus and related species, in Alkaloids. Chemical and Biological Perspectives, Vol. 3 (S. W. Pelletier, ed.), 241-273, Wiley, New York, 1985. 

Such a transformation was applied to the synthesis of Elaeocarpus-AevvveA indoUzine alkaloids grandisine B and... 

Plants of Elaeocarpus species growing in New Guinea yield a number of alkaloids characterized by the unique chromanoindolizidine skeleton. An efficient two-step synthesis of these alkaloids developed by Onaka is based on the known reaction of enamines with salicylaldehyde. ... 

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