Keto cyclopentane-1,2-dione

The mechanism of the reaction of the vinyl carbinol (2) with cyclic 1,3-diketones has been discussed [1077]. New 1,3-dicarbonyl compounds have been condensed with this carbinol. Thus, the reaction with 2-chloro-l,3-cyclopentanedione led to an analog of 18-norestrone (1) with an aromatic ring C [1078]. The condensation of the isothiouronium salt of the vinyl carbinol (2) (see Scheme 38) with 4-acetoxy-2-methyl-l,3-cyclopentane-dione gave an unstable highly unsaturated compound (3) the catalytic hydrogenation and demethylation of which led to 8-isoestrone with an overall yield of 28% on the (2) [1079]. The reaction of the vinyl carbinol (2) with a, y-dimethyltetronic acid led to compound (4). Treatment with pal-ladized carbon and alkaline hydrolysis gave the keto ester (5) and the electrochemical reduction of this yielded racemic bisdehydrodoisynolic acid (6) [1080]. 

Also used as a spectral comparison model for the elucidation of the B and G aflato-xinsss this compound was prepared in a multi-step synthesis. The von Pechmann condensation of phloroglucinol dimethyl ether (59)133 with diethyl cyclopentane-4,5-dione-l, 3-dicarboxylate (41) in acidic solution afforded the /J-ketoester (42), which readily underwent decarboalkoxylation, in a seperate step, to give the keto-coumarin (5). The beauty of this methodology is illustrated by the use of the symmetrical diketoester (41), which of course, only allows for the formation of a single coumarin (von Pechmann) product (42). The regiochemistry of the final product, however, was demonstrated to be the incorrect isomer insofar as the aflatoxin structures were concerned. 

Scheme 3.50 Keto-enol equilibrium in cyclopentane-1,2-dione.

A soln. of LiAlH4 in anhydrous tetrahydrofuran treated dropwise at ca. -10° with BFg-etherate, then a soln. of m-methoxystyrene in tetrahydrofuran added, stirred ca. 1 hr. at room temp, under argon, a soln. of 2-methyl-2-(2-diloro-3-keto-4-diazobutyl)cyclopentane-l,3-dione in dry benzene added dropwise, allowed to stand 3 hrs., the soln. of the resulting intermediate in benzene treated with tert-butyl hydroperoxide, the crude 3 -methoxy-ll)5-diloro-14j5-hydroxy-9,10-seco-... 

The utility of the method of synthesis of fused five-membered rings by reactions between dimethyl 3-ketoglutarate and 1,2-dicarbonyl compounds is further illustrated this year, with syntheses of the tetraketone (105) from the keto-aldehyde (104) and of the propellane (107) from cyclopentane-1,2-dione (106). ... 

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