Spiro tetramers

FIGURE 6.29 Cyclic spiro tetramer 34 and its reduction product, macrocycle 35. 

FIGURE 6.32 Configurationally different spiro tetramers 44a and 44b formed by spiro tetramerization of l,3-bis(5-tocopheryl)propane (43) in a 15 1 ratio in agreement with theory. Reduction of each of the tetramers provides c s-l,2-c s-4,5-tetrakis(5-tocopheryl)cyclohexane (45). The dashed lines separate the two former units of 43, indicating where bond formation during the spiro oligomerization process occurred. 

Rhodium (I)-phosphine systems lead to catalytic tetramerization. For example, the system [RhCl H with 1 to 2 moles of PPh3 is effective in the selective formation of an interesting spiro compound (XV) (152) free from other isomers. Although the detailed reaction path is unknown due to the inaccessibility of the intermediate complexes, the formation of (XV) may be visualized from a tetramer complex as follows ... 

Ackers GK, Holt JM. Asymmetric cooperativity in a symmetric tetramer human hemoglobin. J. Biol. Chem. 2006 281 11441-11443. Jayaraman V, Spiro TG. Structure of a third cooperativity state of hemoglobin ultraviolet resonance Raman spectroscopy of cyanome-themoglobin ligation microstates. Biochemistry 1995 34 4511 515. 

Tetramers containing deoxy-sugars to have been synthesised are O-a-D-Galp-(l->3)-0-a-D-Glg7-(l- 3)-0-a-L-Rh -(l- 4)-D-ribitol, an 5. Pneumoniae polysaccharide unit, and a tetrasaccharide component of the orthosomycins (Chapter 19) containing a spiro-ortholactone feature. 

N-phenylmaleimide was developed for the construction of the spiro-cyclopentaneoxindole scaffold. Duris described a new method for the synthesis of tetramic acids based on an intramolecular Wittig annulation procedure (Scheme 17). ... 

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