Rethrolones synthesis

Rethrolones and Related Compounds.—Electrolysis has featured prominently in two useful syntheses of rethrolones published this year. In one of these approaches 2,5-dimethoxydihydrofuran is first prepared by the anodic oxidation of the appropriate 2,5-disubstituted furan (80) in methanol hydrolysis of the electro-oxidation product with ion-exchange resin, followed by treatment with base, then completes the rethrolone synthesis (Scheme 21). Anodic oxidation of substituted cyclo-pentadienes in HOAc brings about ready introduction (1,4) of two oxygen functions into the diene leading to (81), which by a series of transformations can be converted into the rethrolone (82). ... 

Rethrolones and Related Compounds.—Shono and his co-workers have extended their studies of the synthesis of cyclopentenones via the electrochemical oxidation of substituted furans, and effected a synthesis of 2-alkylrethrolones (Scheme 17), and also of 2-hydroxy-3-methylcyclopent-2-enone (Scheme 18), which is an important flavour compound. 

Nucleophilic additions to the carbon-carbon double bond of ketene dithioacetal monoxides have been reported [84-86]. These substrates are efficient Michael acceptors in the reaction with enamines, sodium enolates derived from P-dicarbonyl compounds, and lithium enolates from simple ester systems. Hydrolysis of the initiEil products then led to substituted 1,4-dicarbonyl systems [84]. Alternatively, the initial product carbanion could be quenched with electrophiles [85]. For example, the anion derived from dimethyl malonate (86) was added to the ketene dithioacetal monoxide (87). Regioselective electrophilic addition led to the product (88) in 97% overall yield (Scheme 5.28). The application of this methodology to the synthesis of rethrolones [87] and prostaglandin precursors [88] has been demonstrated. Recently, Walkup and Boatman noted the resistance of endocyclic ketene dithioacetals to nucleophilic attack [89]. 

Tsuji et al. have further exemplified the palladium(ii)-catalysed functionalization of terminal olefins into methyl ketones, in the synthesis of rethrolones, ° jasmonates ° (Scheme 27), and in a bisannelation sequence. The same group... 

A simple alternative synthesis of the rethrolone skeleton from furans is by conversion into the corresponding 2-furylcarbinol (83) followed by acid-catalysed... 

Cooper and Dolby have outlined a general synthesis of rethrolones which has, as an essential feature, the aldol cyclization of keto-aldehyde (88) with K2CO3 in aqueous dioxan in the presence of a catalytic amount of thiophenol. The attempted cyclization of (88) in the absence of thiophenol instead led to -keto-aldehyde (89),... 

Rethrolones and Related Compounds.— The recent synthesis of 4-substituted-5-hydroxy-3-oxocyclopentenes by acid-catalysed rearrangement of 2-furylcar-binols has now been extended to a useful synthesis of ( )-allethrolone (93), and Naf and Decorzant have published full details of their synthesis of jasmone (95) based on thermal rearrangement of the spiro-intermediate (94) produced by reaction between cyclopenianone and l,4-dibromopent-2-ene. 

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