Izidine alkaloid

Since Huisgen s definition of the general concepts of 1,3-dipolar cycloaddition, this class of reaction has been used extensively in organic synthesis. Nitro compounds can participate in 1,3-dipolar cycloaddition as sources of 1,3-dipoles such as nitronates or nitroxides. Because the reaction of nitrones can be compared with that of nitronates, recent development of nitrones in organic synthesis is briefly summarized. 1,3-Dipolar cycloadditions to a double bond or a triple bond lead to five-membered heterocyclic compounds (Scheme 8.12). There are many excellent reviews on 1,3-dipolar cycloaddition, in particular, the monograph by Torssell covers this topic comprehensively. This chapter describes only recent progress in this field. Many papers have appeared after the comprehensive monograph by Torssell. Here, the natural product synthesis and asymmetric 1,3-dipolar cycloaddition are emphasized.630 Synthesis of pyrrolidine and -izidine alkaloids based on cycloaddition reactions are also discussed in this chapter. 

Isoquinolizidine alkaloids 64 Isorauhimbic acid 16 Isosandwichine 17 Isostephaboline 45 Isostrychnopentamine 20, 38, 160 Isosungucine 20, 38 Isotetrandrine 45 Isovoacangine 16 Isowilfordate alkaloids 86 Izidine alkaloids 69, 70, 96, 97, 103... 

Another application of the [2+2+2] cycloaddition used alkenyl isocyanates 441 and terminal alkynes 390 for the formation of izidine alkaloid skeletons 442 and 443 with a lactam and a vinylogous amide moieties, respectively (Scheme 2-48). ... 

The medicinal uses of pyrrolizidine alkaloids and pyrrol-izidine-alkaloid-containing plants have been questioned, be-... 

Reductive Carbocyclization of Dienes. Carbocyclization-silylation of 1,5- and 1,6-dienes such as 39 (52-58) as well as enynes (59) catalyzed by Cp 2YMe THF or Cp 2LuMe THF is a highly regio- and diastereoselective process, which tolerates various functional groups such as ethers, thioacetals, and tertiary amines in spite of the strong Lewis acidity of the catalysts (Scheme 22). This reaction has been applied to the synthesis of izidine alkaloids such as epilupinine 43 (Scheme 23) (54). 

The most s pificant development of the past decade has been the discovery of oribatid mites as an important new source of what were once regarded as typical frog skin metabohtes. The first unequivocal report of the presence of izidine alkaloids in mites from Japan came from a study of two species... 

It now appears indisputable that all of the izidine alkaloids found in amphibian skins have a dietary source. The history and current status of the dietary hypothesis has been the subject of an important review. ... 

---