Jasmine ketolactone

The direct comparison of 1 and 2 in a variety of RCM reactions also indicates a presumably close relationship between these catalysts (Table 1) [6]. Both of them give ready access to cycloalkenes of almost any ring size > 5, including medium sized and macrocyclic products. Only in the case of the 10-membered jasmine ketolactone 16 was the yield obtained with 2a lower than that with lc this result may be due to a somewhat shorter lifetime of the cationic species in solution. However, the examples summarized in Table 1 demonstrate that the allenylidene species 2 exhibit a remarkable compatibility with polar functional groups in the substrates, including ethers, esters, amides, sulfonamides, ketones, acetals, glycosides and even free hydroxyl groups. 

Specific enolates by conjugate (Michael) addition An intermediate in Corey s ginkgolide synthesis A synthesis of jasmine ketolactone Tables of Enol Equivalents and Specific Enolates Modern Use of Specific Enolate Equivalents... 

SCHEME 20.23. The synthesis of ( )-jasmine ketolactone by the transannular Michael reaction. 

One such example is the synthesis of ( )-jasmine ketolactone by Shimizu and Nakagawa. The transannular cychzation of macrocychc lactone 89 was initiated by treatment with NaH in toluene at 90°C to give ( )-jasmine ketolactone in 69% yield (Scheme 20.23). The reaction was highly diastereoselective as only the trans-isomtx was formed. 

Other interesting synthetic applications of the ketone-derived enamine alkylation are found in the monomethylation of steroid enamines (249), extension of the benzylation reaction (250) to a ferrocene derivative (251), the use of a-bromoesters (252) and ketones (252) or their vinylogues (25J), in the syntheses of alantolactone (254-256), isoalantolactone (257), and with a bridged bis-enamine (258). The use of bifunctional alkylating agents is also seen in the introduction of an acetylenic substituent in the synthesis of the characteristic fragrant constituent of jasmine (259), the synthesis of macrocyclic ketolactones (260), the use of butyrolactone (261), and the intermolecular or intramolecular double alkylations of enamines with dihalides (262). 

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