Kagan ’ s ether

Acid treatment of arylethanals may lead to 2-phenylnaphthalenes or l,2,9,10-tetrahydro-l,9-epoxydibenzo[a,e]cyclooctenes (Kagan s ether). 2-Phenylnaphthalenes were obtained by a C-condensation of the enolated form on the keto form. The resulting aldol condensation product underwent an intramolecular reaction to give, after rearomatisation, the 2-phenylnaphthalenes, Fig. (1). 

Fig. (2). Mechanim of formation of Kagan s ether (example is given with boron tribromide as Lewis acid)...

More curiously, N-tosylated phenylalanine derivatives [10] and phenyllactic acid [11] can also be converted into 2-phenylnaphthalene in moderate yields whereas 3,4-dimethoxyphenyllactic acid treated with boron tribromide gives Kagan s ether in almost the same yield as 3,4-dimethoxyphenylethanal does [11]. In these cases, the decomposition of aryllactic acid or alanine derivatives may give arylethanal with the formation of water and carbon monoxide, Fig. (4). 

Kagan s ether structurally related compounds have not been found in Nature but their nitrogen analogues belong to the pavine alkaloid family. Pavinan and isopavinan alkaloids can be formally viewed as oxidatively cyclised 1-benzyl-1,2,3,4-tetrahydroisoquinolines and are most frequently obtained by acid-catalysed cyclisation of appropriately oxidised congeners of these isoquinolines [13]. Numerous attempts have been made to convert Kagan s ethers into pavine, but all were unsuccessful [4]. 

Cram has prepared a host system consisting of four linked dibenzofurans (430). One variation was found to form a complex with guanine in methanol <92JA10775>. Bisdibenzofuran (431), a derivative of Kagan s ether, is a molecular tweezer that binds to trinitrobenzene <90JA5655>. 

Functionalized analogues of Kagan s ether (159) have been prepared via a one-pot cascade dimerization of orf/to-alkynylbenzaldehydes in acetic acid, with aqueous HBF4 catalysis. ... 

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