Hop ether

Secologanin on enzymic cleavage, acid treatment, and oxidation gave elenolide (248), and the sequence established the chirality as shown at the point of attachment of the side-chain.775 [10-13C]Secologanin was synthesized in a seven-step process from ethylene acetal.776 Hop ether (249), the irioid most simply related to geraniol, was synthesized in six steps from the protected lactol form of 3-formyl-2-methoxy-carbonylcyclopentan ol.7 7 7... 

Numerous synthetic applications of the inteimolecular Pauson-Khand reaction have been reported. Pauson has reported a number of very direct tqrplications of cycloadditions of ethylene in the synthesis of prostanoids and jasmone analogs (e.g. equations 15 and 16). - This is a reliable entry to 2-sub-stituted cyclopentenones. The suitability of cyclopentene and dihydrofuran as substrates has permitted the extension of this work to the preparation of still further varieties of prostaglandin analogs (e.g. equations 27 and 51). Simple 4,5-disubstituted 2-cyclopentenones are not as directly accessible, but may be prepared from the cycloaddition products of norbomadiene (equation 45). A sequence of conjugate addition followed by retro-Diels-Alder reaction affords the product (Scheme 5). Dihydrofuran cycloadditions have been used by Billington in the syntheses of the antibiotic methylenomycin B (Scheme 6), as well as cyclomethylenomycin A (synthetic precursor to the antibiotic methylenomycin A), cyclosarko-mycin (precursor to the antitumor agent sarkomycin) ° and the iridoid Jq>anese hop ether. ... 

Figure 1. Structures of hop oil components. Key I, humulene II, humulene epoxide I III, humulene epoxide II IV, humulol V, humulenol II VI, humula-dienone VII, a-eudesmol VIII, -eudesmol IX, hop ether X, karahana ether XI, p-ionone and XII, j3-damascenone.

These compounds may well have an effect on the hop aroma of beer but if they are responsible for the traditional "kettle hop" aroma, then the concentration of humulene in hops should not be so important. Further, from Table 111 the concentration of hop ether and karahana ether in hop oils does not correlate well with aroma quality. Tressl (17) has noted that the concentrations of these two ethers go up dramatically as hops age. 

Japanese Hop Ether has been prepared by both an intermolecular and an intramolecular PKR. In Kerr s intramolecular version, it... 

A total synthesis of cyclic acetal of 2-carboxymethyl-3-formylcyclopentanol which is then converted into, /-hop ether as indicated in Scheme 31. 

Hop ether (136) and karahana ether (139) are monoterpenoid compounds which occur in Japanese hop (Shinshu-wase) 426), while the occurrence of (-h)-matatabi ether (138) and of its isomer (137) is limited to the essential oil of Actinidia polygama Franch. et Sav. (Ternstroemiaceae) 261, 716). 

Phosphinothioic amides are highly effective reagents for the alkylidenation of ketones, and the method has been developed as a means of methylenation coupled with optical resolution. The reaction of the anion of the phosphinothioic amide (21) gives the diastereoisomeric mixture (22), which, after separation, can be converted into the optically active olefins (23). The method has been applied to the synthesis of the (+)- and ( —)-iridoid monoterpene hop ether (24), and can be extended to alkylidenation with resolution. 

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