Stemona alkaloids Stemoamide

Allenols may be carbonylated under quite different conditions. Using Rus (CO)i 2 as the catalyst, unsaturated lactones can be synthesized efficiently." The reaction may also be extended to lactams." This cyclization, combined with an intramolecular propargylic Barbier reaction has been used in syntheses of mintlactone 4.111 from allenol 4.110 (Scheme 4.43)" " and its diastereoisomer, isomintlactone," as well as the stemona alkaloid, stemoamide 4.115 from allenol 4.113 (Scheme 4.44)," and in the skeleton of stenine." A different synthesis of stemoamide can be found in Chapter 8, Scheme 8.112. 

Jacobi and co-workers ° described the total synthesis of racemic stemoamide, a member of the stemona alkaloids isolated in 1992 from Stemona tuberosa, and an enantioselective route to (-)-stemoamide. The starting alkyne oxazoles 200 and 203 were prepared from y-chlorobutyryl chloride 199 in five steps (Fig. 3.60). 

Stemoamide type Stemona alkaloids Occurrence and Properties. 

The tricyclic alkaloid stemoamide (15) is a typical representative of this group of Stemona alkaloids and it has been synthesized several times over the last few years, including some very efficient approaches. 

S. tuberosa provided most of the isolated Stemona alkaloids, followed by S. japonica, and S. sessilifolia. The phytochemical study of Croomia is restricted to C. heterosepala and C. japonica, from which only two Stemona alkaloids were isolated [croomine (29) and didehydrocroomine (34)], both from the tuberostemospironine group (III). Alkaloids from the stemoamide group (II) were found in eight of the twelve investigated Stemona species, while the alkaloids from the other groups were isolated from only two to four Stemona species (Table XXV). 

Ring-Closing Metathesis of Enyne Precursor The first example of target-directed synthesis using enyne metathesis is the total synthesis of (—)-stemoamide 179, an alkaloid isolated from the roots of Stemona... 

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