Asymmetric oxygen-functionalization

Satoh T, Miura M (2007) Catalytic Arylation and Vinylation Reactions Directed by Anionic Oxygen Functions via Cleavage of C - H and C - C Bonds. 24 61-84 Savoia D (2005) Progress in the Asymmetric Synthesis of 1,2-Diamines from Azomethine Compounds. 15 1-58... 

Figure 26. XPS data in the carbon 1 s region for a UHV cleaved graphite reference (HOPG) and a carbon black sample used in the titration experiments of Fig. 25. The arrow marks the position of the graphite surface plasmon. The top section of the modified spectrum in the high-binding energy side reveals several weak peaks for oxygen functional groups after removal of the asymmetric line profile from the main peak.

Furthermore, it is known that the presence of an oxygenated function on a stereogenic center exerts a strong influence on the 1,2-asymmetric induction, affording high selectivity (95%). For example, in iodohydrin formation from acyclic allylic alcohols 19, a, 2-syn selectivity of 90 - 99% is observed26. 

The 1,2-asymmetric induction exerted by an oxygenated function in the allylic position mainly produces the 2,3-m-isomer while other stereogenic centers present in the substrate have little overall effect on the diastereomeric ratio, such that the 2,3-cis disposition predominates over the 2,5-Irons disposition34-36. 

On the other hand, higher 1,2-asymmetric induction is observed for the cyclization of 5-aIkenols which bear an oxygenated function at C-4. Thus, treatment of 5-hexen-1,4-dioI (3) with phenyl-selenyl triflate in dichloromcthanc at —78 °C gives the corresponding tetrahydro-2/f-pyran 4 in 52% yield as a 91 9 (cis/trans) mixture. The preferential 2,3-cis relationship can be explained by analogy with the halocyclization of 4-pentene-l,3-diols (see Section 4.6.2.1.1.3.)19. 

Ohta, T. Miyake, T. Seido, N. Kumobayashi, H. Takaya, H., Asymmetric Hydrogenation of Olefins with Aprotic Oxygen Functionalities Catalyzed by BINAP-Ru(II) Complexes. J. Org. 

Kagan studied the base-catalyzed cycloaddition reaction of anthrone and N-methylmaleimide (15) [16]. In contrast to the above reactions,2 and 3 gave (S,R)-16, while 1 and 4 gave (P,S)-16. The oxygen functionality at C(6) of the catalysts might be participating in the asymmetric induction. Besides the alkaloids, (S)-prolinol also gave R,S)-16 in 47% ee. 

Allylation. Long-range asymmetric induction by an oxygen functionality is observed in the reaction of allylstannanes with aldehydes using tin(IV) bromide as catalyst. Irrespective of the original configuration of the allylic double bond, the... 

If the oxidized carbon nanofibers are calcined at 573 K, the shoulder at 1740 cm and the band at 1720 cm becomes less pronounced (Fig. 4). The phenolic and asymmetric and S5nnmetric NO2 stretching vibration peaks have disappeared completely. Thus ketone, carboxylic, phenolic and nitro groups decompose if the carbon nanofibers are calcined at 573 K. The peak that remains at 1720 cm" is most likely due to lactones because these groups decompose between 600 and 950 K [31]. If the temperature is increased further to 873 K, the shoulder and peak at 1740 cm" and 1720 cm" have disappeared completely. It follows that the majority of the surface oxygen functional groups decompose at 573 K. 

Marine macrolides have numerous asymmetric centers, oxygenated function-ahties including alcohols, carbonyl groups, the tetrahydropyran moiety, di-and trisubstituted alkenes, and macrocycUc lactones. For completion of their total synthesis, efficient and stereoselective introduction of these characteristic units should be crucial. Recently, an excellent review on asymmetric synthesis of 1,3-diol, macrolactonization, and glycosidation in the syntheses of macrolides has been pubUshed by Nakata [5]. The multisubstituted tetrahydropyran moieties are often found in the marine macrohdes, and the efficient preparation of these moieties is recognized as the key reaction in their total synthesis. In this decade, efficient methods for their stereoselective construction have been developed and used in the total synthesis of marine macrolides, wherein the relative configuration of 2- and 6-substituents is pivotal. In this section, recent progress in the preparation of tetrahydropyrans is described (for a previous review on the preparation of tetrahydropyrans, see [9]). 

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