Tropolone ethers

Scheme 2 Asymmetric induction in the disrotatory photocyclization of tropolone ethers...

Similar irradiation of the 1 1 complex of tropolone ether 10b and host compound 8 led to photoproducts 11b (100% ee) and 12b (72% ee) in 12 and 14% yields, respectively. The authors interpreted these reactions as follows disrotatory electrocyclic closure of tropolone derivative 10 to afford photoproduct 11 in the inclusion crystals occurs in only one direction owing to the steric hindrance of host 8. This interpretation appeared to be reasonable based on an examination of the X-ray crystal structure study of the inclusion complex [18]. Formation of keto-ester 12 takes place by a more complex mechanism... 

Furthermore, the homologous complex 286 condenses with ethyl orthoformate to give, in the course of a new y-tropolone synthesis, tropolone ether 287 by O-ethylation it is transformed to tropylium salt 288 (Scheme 72 70JA6382) the corresponding tropone complex was synthesized from dibenzotroporic and Cr (CO)6 [83AG(S)734]. 

There is also rapid development in the domain of standard silica-based zeolites. Their versatility can be extended by imprinting. For instance, Davis and Katz [15] recently successfully carried out imprinting and obtained a silica framework with pore walls anchoring three aminopropyl groups in cavities. Another achievement was reported by Ramamurthy, Schefer and coworkers [16]. The latter authors were able to obtain 90% diastereomeric excess of a product of the photochemical reaction in a commercially available zeolite containing chiral tropolone ether 433 in its pores. 

Joy, A., Scheffer, J.R. and Ramamurthy, V. (2000) Chirally modified zeolites as readion media photochemistry of an achiral tropolone ether. Organic Letters, 2, 119-121. 

NaY zeolites modified with (— )-ephedrine or (— )-norephedrine showed even better performance in the photolysis of chiral tropolone ether 22c immobilized in the supercage, affording 23c in 90% de. In contrast, irradiation of 22c in solution or on a silica surface in the presence of enantiopure ephedrine or norephedrine gave 1 1 diastereomeric mixtures. 

Tropolone ethers have served as useful probes of asymmetric induction using several different supramolecular approaches [49]. Solid-state photolysis of 1 1 host-guest complexes of tropolone methyl ether 25 with (R,R)-( — )-4 caused disrotatory [2 + 2] photocyclization to 26 followed by transformation to afford... 

The ionic chiral auxiliary approach was also applied to the enantioselective photocylization of tropolone. Irradiation of salt crystals of tropolone ether carboxylic acid 29 with several chiral amines afforded the enantiomerically enriched secondary products 31 [52]. The best results were obtained with optically pure 1-phenylethylamine and l-amino-2-indanol, which gave optical yields in the 60-80% ee range depending on the extent of conversion. 

Tropolone ether 35 undergoes a disrotatory 4tt electrocyclic ring closure to yield the corresponding bicyclo[3.2.0] product 36 (Scheme 18) [284,285]. The chirality... 

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... 

With (+)-ephedrine as a modifier on NaY, an ee of 69 % for one of both enantiomers was obtained. With tropolone ethers already containing a chiral carbon atom, a diastereomeric excess of 90% was observed. 

Irradiation of the achiral tropolone ether (134) in an active host compound results in ring closure of the tropolone ether to afford products with high ee. ... 

An X-ray study has shown that the orange-red base imerubrine, also present in A. imene and A. rufescens, possesses the remarkable tropolone ether structure (54). It is the first example of a new isoquinoline alkaloidal type for which the general term tropoloisoquinoline has been proposed. ... 

Thermal rearrangements of tropolone ethers have been described. Thermolyses of the 7-substituted tropolone propargyl ethers (135 R = Cl, Ph R = H) give lactones (136 R = Cl, Ph) via [3, 3] shifts and cyclization. However, lactones (136 R = Ph, Cl) are also formed on thermolysis of the 3-substituted tropolone propargyl ethers (135 R = H R = Ph or Cl). The formation of these lactones from the 3-substituted tropolone ethers was interpreted in terms of a [3,7]shift to give the... 

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