Samarium occurrence

The occurrence of the indole subunit is well established within the class of natural products and pharmaceutically active compounds. Recently, the Reissig group developed an impressive procedure for the assembly of highly functionalized in-dolizidine derivatives, highlighting again the versatility of domino reactions [8]. The approach is based on a samarium(II) iodide-mediated radical cydization terminated by a subsequent alkylation which can be carried out in an intermolecular - as well as in an intramolecular - fashion. Reaction of ketone 3-11 with samarium(ll) iodide induced a 6-exo-trig cydization, furnishing a samarium enolate intermediate... 

ISOTOPES There are 41 known isotopes of samarium. Seven of these are considered stable. Sm-144 makes up just 3.07% of the natural occurring samarium, Sm-150 makes up 7.38% of natural samarium found on Earth, Sm-152 constitutes 26.75%, and Sm-154 accounts for 22.75%. All the remaining isotopes are radioactive and have very long half-lives therefore, they are considered "stable." All three contribute to the natural occurrence of samarium Sm-147 = 14.99%, Sm-148 = 11.24%, and Sm-149 = 13.82%. 

The samarium enolate radicals were also trapped intermolecularly, with formation of new carbon-carbon bonds, by quenching the reactions with suitable electrophiles The occurrence of these tandem rearrangements was possible because the samarium(II) iodide acted as a clean one-electron reductant and also generated the metal enolates. 

The known structures of the lanthanide and actinide metals are indicated in table 5.01, from which it will be seen that the structures characteristic of the true metals, and particularly the hexagonal close-packed arrangement, are common. Polymorphism, however, is of frequent occurrence among these elements, and plutonium, for example, crystallizes in no fewer than six modifications—the A1 and A2 structures indicated and four others of greater complexity. Praseodymium, neodymium and samarium are of interest in that they possess close-packed structures in which the sequence of layers is... 

Francois et al. (1990) investigated the occurrence of CeNiSi2 type for samarium-manganese-germanium combinations for alloys annealed at 1173K (SmMno.4oGe2 a= 0.4194, i = 1.633, c = 0.4062). 

---