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Spiro centers

Only three examples of ibogan-type oxindole alkaloids are known, and two of them, crassanine (156) and tabemoxidine (155), were found in Tabernaemon-tana. Crassanine (C23H30N2O5, MP 191°C, [a]D +21°) was isolated in minute amounts by Cava et al. from T. crassa (79). Its IR spectrum indicated the presence of two carbonyl groupings (1739 and 1709 cm - ), while its UV spectrum was almost superimposable on that of known 10,11-dimethoxyoxindoles such as kisantine (200). In addition to the carbomethoxy methyl at 3.47 ppm and two aromatic methoxyls at 3.83 ppm (6H), the H-NMR spectrum of 156 exhibited two singlets (1H) at 6.50 and 7.01 ppm and the low-field oxindole NH at 9.30 ppm. The latter values are similar to those recorded for kisantine, and on this basis Cava et al. proposed the structure 102 for crassanine. To date, no evidence is available on the configuration at the C-7 spiro center. [Pg.97]

Spiro-shaped HTMs have been studied extensively (Scheme 3.16) [88,89], The introduction of a spiro center improves the thermal stability of the amorphous state without significantly changing charge-transport properties. Compared with using NPD, TPD HTMs, using 43 in ITO/HTM/Alq3/LiF/Al devices showed very high luminescent efficiency [90]. [Pg.317]

U.S. 6,361,884 Partially conjugated polymers with spiro centers and their use as electro-luminescent materials... [Pg.650]

An example of N-dealkylation of an amine adjacent to a tertiary carbon can be found in the metabolism of synthetic opiod, alfentanil. The CYP3A4-catalyzed oxidation of the opiod alfentanil follows two major pathways (119) N-dealkylation to form no-ralfentanil and cleavage of the spiro center to generate N-phenylproprionamidc. Moreover,... [Pg.78]

V-phenyIpmprionamidc is found to come directly from alfentanil and not from noralfen-tanil. The mechanism of how the carbon-nitrogen of the spiro center is cleaved has not appeared in the literature. A possible mechanism would entail initial hydroxylation of a ring carbon adjacent to the piperdine nitrogen, followed by elimination of hydroxide to form the imine then rearrangement to the enamine, and finally elimination of the amide as indicated in Figure 4.56. [Pg.79]

In order to obtain asymmetric spiro compounds, there are two different possibilities. First, one can connect two different chromophores via a common spiro center. The thiophene compounds 39a and 39b are one example [84, 85]. Second, one can connect two equal but asymmetric chromophores. Based on this principle are Spiro-PBD (40), spiro-bridged bis(phenanthrolines) (41) [86], and the branched compounds Octol (42a) and Octo2 (42b) [87]. Because of their symmetry, these molecules are chiral. The glass transition temperatures of 40 and 42b are reported to be 163 and 236°C, respectively [88], Unfortunately, reports on the thermal properties of 39 and 41 are lacking. [Pg.115]

Failed even after equilibration, both equatorial and axial sulfoxide isomers had the C-is spiro center in the anomeric configuration... [Pg.3]

The hole conductor has a spiro-center (a tetrahedral carbon linking two aromatic moieties) that is introduced in order to improve glass forming properties and prevent crystallization. Crystallization is undesirable since it impairs the formation of a good electrical contact between the 2 surface and the hole transporting... [Pg.566]

Fig. 12. Five fused four-membered cycles with magnesium atoms as spiro centers and methyl bridges in the dimeric [(MeSi)(NrBu)3(AlMe2)(H)MgMe]2 (75). Fig. 12. Five fused four-membered cycles with magnesium atoms as spiro centers and methyl bridges in the dimeric [(MeSi)(NrBu)3(AlMe2)(H)MgMe]2 (75).
Berberis empetrifolia yielded the unstable base coyhaiquinine (471), C26H25N05. The structure was proposed principally from the completely resolved 200-MHz FT NMR spectrum, and the alkaloid was shown to have syn geometiy at the spiro center by NMR correlations with the related syn compounds 46,107,149,262, and 359 and with the anti alkaloids 108 and 109. Insufficient material was available for exact determination of optical rotation, but the general form of the CD curve resembles that of coyhaiquine (107), indicating the absolute configuration shown (554). [Pg.179]

The spiro carbon is a stereogenic center in spiropyrans, but because of the achiral structure of the open merocyanine form, the photochromic process will always lead to racemization unless additional chiral moieties are present. When a chiral substituent was introduced, remote from the spiro center, it was possible to isolate diastereo-isomers of the spiropyrans, but rapid epimerization at the spiro center occurred.1441 Diastereoselective switching was successful with 28, in which a stereogenic center was present close to the spiro carbon (Scheme 15).[45] Distinct changes in CD absorption at 250 nm were monitored upon irradiation with UV (250 nm) and with visible light (>530 nm) and a diastereomeric ratio of 1.6 1.0 was calculated for the closed form 28. Furthermore, a temperature-dependent CD effect was observed with this system it was attributed to an inversion of the diastereomeric composition at low temperatures. It might be possible to exploit such effects in dual-mode chiral response systems. A diastereoselective ring-closure was also recently observed in a photochromic N6-spirobenzopyran tricarbonyl chromium complex. 451 ... [Pg.142]

Controlling the coordination of palladium intermediates with silver salts was the key to developing highly diastereo- and enantioselective Heck reactions.58 For example, the presence of silver phosphate in the key cyclization step during the synthesis of various alkaloids reversed the stereochemistry at the newly created spiro center (Scheme 10.33).59... [Pg.300]

More complex tin-rich rings containing S, Se, and Te are known, as are systems in which heterocycles are linked by a spiro center. In the latter case, three compounds of the same composition, RgSnJXi (X = S, R = Pr and Bu X = Se, R = (Pr), have been synthesized by the routes shown in Eqs. (45) and (46). The compounds are conformationally distinct in the solid state (Fig. 7), but these forms equilibrate in solution (183). [Pg.202]

Cyclopropylidenespiropentane (6) contains a central three-membered ring with an exocyclic double bond which is able to conjugate through the spiro center. In 7-cyclopropylidenedispiro[2.0.2.1]heptane (7) and 1-cyclopropylidenedispi-ro[2.0.2.1]-heptane (8) the additional spiro-connected three-membered ring introduces more strain and changes of hybridization. [Pg.217]

The total synthesis of (+)-deethylibophyiiidine was achieved by J. Bonjoch et ai. using a tandem Pummerer rearrangement/thionium ion cyclization to generate the quaternary spiro center.The suifoxide was exposed to an equimoiar mixture of TFA/TFAA and heated for 2h to form the quaternary stereocenter at C7 with the desired stereochemistry, but at C6 a mixture of epimers were formed. Reductive desuifurization with Raney-Ni followed by photochemical rearrangement afforded the natural product. [Pg.369]

The efficiency of this hyperconjugation must depend essentially on the geometric configuration of the LEPs of the N(l ) and 0 atoms and the Cspi[O-0 and Cspin,-N(l ) bonds, on the one hand, and on the electronic state ofthe N and 0 atoms, on the other hand. In all of the SPs studied, the spiro center has a sterically strained structure. Because of the rigidity of the tetrahedral structure of the spiro center and the similar conformation of the indoline ring, the Cspiro—O bond makes an angle (t) of 165-171° with the LEP of the N(l) atom (Table 1). [Pg.301]

Effect of the Nature of Heteroatoms in the Spiro Center on the Structure and Photochemical Properties of Spiropyrans... [Pg.315]

The considerable influence of specific rt-a orbital interactions of heteroatoms in the spiro center of indoline SPs on the structure and photochemical properties of these compounds suggests that new classes of photochromic SPs can be obtained by changing heteroatoms and their relative orientation in the spiro center. In this section, we will examine the structure of SPs containing different heteroatoms in the spiro center. [Pg.315]

It was demonstrated in Section 7.2.1.3 that the efficiency of orbital hyperconjugation in the spiro center depends both on the geometric configuration of the LEPs of the heteroatoms and adjacent bonds and on the electronic properties of the heteroatoms. Since symmetrical spiropyrans contain the same heteroatoms in the spiro center, efficiency of n-a interactions depends mainly on the electronic state of the heteroatoms as determined by the nature and positions of substituents in the benzopyran moiety. [Pg.317]


See other pages where Spiro centers is mentioned: [Pg.226]    [Pg.97]    [Pg.114]    [Pg.189]    [Pg.144]    [Pg.103]    [Pg.714]    [Pg.483]    [Pg.864]    [Pg.37]    [Pg.103]    [Pg.365]    [Pg.191]    [Pg.224]    [Pg.424]    [Pg.864]    [Pg.104]    [Pg.1057]    [Pg.2]    [Pg.539]    [Pg.65]    [Pg.66]    [Pg.300]    [Pg.305]    [Pg.317]    [Pg.317]    [Pg.317]    [Pg.318]    [Pg.318]    [Pg.322]   
See also in sourсe #XX -- [ Pg.301 , Pg.306 , Pg.315 , Pg.317 , Pg.322 , Pg.325 , Pg.329 ]




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