Syntheses Utilizing Fulvenes

Fulvenes may readily be obtained from cyclopentadiene and aldehydes or ketones  

Sodium, potassium, organolithium compounds, and UAIH4 react with fulvenes to 

Some transition metal carbonyls may also form cyclopentadienyl derivatives with fulvenes. Most commonly, the solvent is the source of hydrogen. In the absence of the solvent, disproportionation reactions occur [equations (9.42) and (9.43)]. 

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The utility of this method depends on the reaction conditions, on the type of alkyllithium, i.e. methyl- or butyllithium, and on the halomethane used for the synthesis of methylli-thium" (for a detailed discussion see Houben-Weyl, Vol. 4/3, pp 225-228 and Vol. E19b, pp 1505-1506). Chlorocyclopropanes 1 were prepared via addition of dichloromethyllithium (from dichloromethane and butyllithium or lithium diisopropylamide) to fulvenes followed by the cyclization of the adducts. ... 

Further general route to 2-alkyl-2-butenolactones via the retro Diels-Alder reaction was developed, Fig. 5. [23], Hydrolysis of a known lactone (15), subsequent esterification with diazomethane, and treatment with dihydropyran afforded a stereoisomeric mixture of pyranyl ether. Alkylation of the pyranyl ether with various alkyl halide yielded alkylated products (16). The retro Diels-Alder reaction of 16 was performed by heating at 200-280 °C in a sealed tube to give 2-alkyl-2-butenolactones (17). The utility of the butenolactones was demonstrated by the synthesis of hinokinin (18) and dehydrolappaol A dimethyl ether (19). Similarly rather mild, simple synthesis of a-methylene-y-alkylbutyrolactones was deviced using dimethyl-fulvene as a protective group for the double bond, Fig. 6. [24]. The... 

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