Ether tropolone alkyl

An example of the use of this approach in the disrotatory photocyclization of tropolone alkyl ethers is shown in Scheme 2. Thus, irradiation of the 1 1 complex of a-tropolone alkyl ether 10a with host compound 8 in the solid state gave photoproducts 11a of 100% ee and 12a of 91% ee in 11 and 26% yields, respectively [17]. 

Keywords tropolone alkyl ether, inclusion crystal, [2+24]photocycloaddition... 

Figure 41 Photocyclization of tropolone alkyl ether within X- and Y-zeolites. The product configuration is arbitrarily assigned based on HPLC retention time. The nature of the favored enantiomer is reversed between wet and dry zeolites and between NaY and NaX. The extent of ee depends on water content, the nature of the cation, and the number of cations (NaY versus NaX).

When the photocyclization reaction of tropolone alkyl ethers 62a and 62b, which produces the corresponding cyclization product 63 and its ring-opened derivative... 

The next example deals with the enantioselective photocyclization of a-tropolone alkyl ethers [182]. Cyclization occurs through an allowed 4e -disrotation that can result in opposite optical isomers depending on the direction of rotation (Sch. 37). Racemic products are obtained in solution, but irradiation of crystalline inclusion complexes of a-tropolone alkyl... 

Figure 1 An adsorption (top)-desorption (bottom) model for chiral induction on a zeolite surface, incorporating a reactant (tropolone alkyl ether, shown at the left), a chiral inductor (with four different substituents, at the right), and a cation (small ball on the surface). Tropolone s carbonyl and ether oxygens hydrogen-bond to chiral inductor, while its tt system interacts with zeolite s cation ion. ...

As briefly mentioned above, Takeshita et al. reported the first enantiodifferentiat-ing photoisomerization of tropolone derivatives to the optically active bicyclo[3,-2.0]heptadienones in 1980 [99], but the product ee and detailed chiral discrimination mechanism have not been determined until recently. Ramamurthy and coworkers reinvestigated the photobehavior of tropolone alkyl ethers in a-, (3-, and y-CDx cavities [102]. 

Irradiation of tropolone alkyl ether 22 (Scheme 14) led to a 4ir-disrotatory ring closure to yield bicyclo[3.2.0]heptadienone 23 with two chiral centers, while prolonged irradiations led to the formation of a secondary product 24 [76-78]. As the same photocyclization was performed in chirally modified zeolites, it is interesting to compare the asymmetric photochemical behavior of 22 in the distinctly different chiral confined media of zeolites and cyclodextrins. Even in the... 

In principle, enantiomerically pure cyclized products from tropolone ethers can be obtained by controlling the mode of ring closure. On the basis of this premise, the observed selectivity within zeolites could be rationalized. When tropolone alkyl ether is adsorbed on a surface, cyclization inward or outward is... 

Based on the observation that the best ee is obtained with bifunctional chiral agents (ephedrine, pseudoephedrine, norephedrine, and valinol see Scheme 43), we tentatively conclude that a multipoint interaction between the reactant molecule, the chiral inductor, and the zeolite interior is necessary to induce preferential adsorption of tropolone alkyl ether from a single enantiotopic face. The dependence of chiral induction (% ee) on the nature of cations (Scheme 45) suggests a crucial role of the cation present in the supercages in the chiral induction process. This is further strengthened by the results observed with wet and dry zeolites. The presence of water decreases chiral selectivity (Scheme 45). Water molecules... 

Figure 13 Adsorption of tropolone alkyl ether (TAE) on a surface. The chiral inductor may control the enantiotopic face by which TAE adsorbs. In the absence of a chiral inductor, TAE will show no preference for adsorption from either enantiotopic face. Note that the same chiral inductor interacts differently when the TAE adsorbs through different enantiotopic faces.

Photoreaction of Tropolone Alkyl Ether, Cycloocta-2,4-dien-l-one and Pyridone... 

A study has been reported on the photochemistry of tropolone alkyl ethers within a-, p, and y-cyclodextrins. Moderate asymmetric induction in the bicyclic products 224 were observed in some cases. ... 

Upon photolysis, tropolone alkyl ether 7 undergoes intramolecular 4n elect-rocyclization to afford chiral bicyclo[3.2.0]heptadienone 8, which rearranges to compound 9 upon prolonged irradiation (Scheme 6). The photocyclization of CD-complexed tropolone methyl ether 7a was hrst studied by Takeshita and coworkers [46]. They found that the formation of CD complex improves the yield of the optically active product 8a, but the ee value was not quantitatively determined. 

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