Cyclopentenones, 3-alkyl-4- synthesis

A Michael addition of the silyl enolate was employed in a short synthesis of ( )-methyl jasmonate from cyclopentenone (eqs 9 and 10). This convergent scheme was carried out in three steps conjugate addition of methyl Q -(methyldiphenylsilyl)lithioacetate to cyclopentenone, alkylation of the resulting enolate with (Z)-l-bromopent-2-ene, and desilylation with potassium fluoride ( )-ethyl jasmonate was prepared in a similar fashion. In the conjugate addition step, the Q -(methyldiphenylsilyl)ester gave superior results to those obtained with the a-trimethylsilyl esters. 

Group IV substituted, 1, 609-614 Cyclopentenone, 2-alkyl-4-hydroxy-synthesis, 1, 424... 

Castagnino, E., Corsano, S., and Strappavecchia, G.P., The preparation of a novel oxo-cyclopenten-2-phosphonate derivative, useful intermediate for 2-alkyl-substituted cyclopentenones synthesis, Tetrahedron Lett., 93, 1985. 

The alkyl allenyl ethers whose chemistry has been discussed are readily prepared and are useful for the synthesis of diverse cyclopentenones, as racemates or in enan-tiomerically enriched form. It is worth noting that silyl allenyl ethers allow entry into a distinct mechanistic manifold [16]. Triisopropylsilyloxyallene 47 can be deprotonat-... 

The first diastereoselective total synthesis of ( )-guanacastepene A (rac-187) was published in a series of papers by Danishefsky and co-workers [107-110]. The tricyclic carbon framework was assembled by interplay of enolate alkylations and ring-closing carbon/carbon double bond forming reactions (Fig. 19). Commercially available cyclopentenone 90 was utilized as the A-ring precursor. 

Davis et al. [88] described the asymmetric synthesis of a-substituted primary sulfonamides involving the diastereoselective a-alkylation of N-sulfonylcamphor-imine dianions, while Huart and Ghosez reported an enantioselective synthesis of bicyclic cyclopentenones via a stereoselective 1,4-addition of metallated enan-tiopure sulfonamides to cyclic enones [89]. 

A total synthesis of ( )-aromatin has utilized the lithium anion of the dithiane of (E)-2-methyl-2-butenal as a functional equivalent of the thermodynamic enolate of methyl ethyl ketone in an aprotic Michael addition (Scheme 189) (81JOC825). Reaction of the lithium anion (805) with 2-methyl-2-cyclopentenone followed by alkylation of the ketone enolate as its copper salt with allyl bromide delivered (807). Ozonolysis afforded a tricarbonyl which cyclized with alkali to the aldol product (808). Additional steps utilizing conventional chemistry converted (808) into ( )-aromatin (809). 

The lithiated sulfone 413 has been alkylated with alkyl bromides623 in the presence of HMPA and with 1,4-dihaloalkanes623,624, acting as an acyl dianion. For instance, treatment of intermediate 413 with the dimesylate 414625 has been applied to the synthesis of the cyclopentane derivative 415, a precursor in the synthesis of 3-oxocarbacyclins (Scheme 107)625. Compound 415 was hydrolyzed to the corresponding cyclopentenone with 50% sulfuric acid in ethanol. 

Vinyllithiums of type 663 (R2 = R3 = H) reacted with primary alkyl bromides, carbonyl compounds, carbon dioxide, DMF, silyl chlorides, stannyl chlorides, disulfides and phenylselenyl bromide142,970-979. Scheme 173 shows the synthesis of dihydrojasmone 669 from the corresponding 1,4-diketone. a-(Phenylsulfanyl)vinyllithium 665, prepared from phenyl vinyl thioether, reacted with hexanal and the corresponding adduct 666 was transformed into its acetoacetate. This ester 667 underwent a Carrol reaction to produce the ketone 668, which was transformed into the cyclopentenone 669 by deprotection either... 

OL, -Bifunctionalization of cyclopentenone.1 Although simple ester enolates do not undergo conjugate additions, the enolate of 1 undergoes conjugate addition to cyclopentenone in THF/HMPT (3.3 1) at -20°. This reaction coupled with in situ enolate alkylation provides a notably short synthesis of methyl jasmonate (3). 

Michael additions. Gerlach and Kiinzler report that the lithium enolate of S-t-butyl thioacetate undergoes 1,4-addition to cyclopentenone. They have extended this Michael reaction to a synthesis of methyl jasmonate (5), based on the similar conjugate addition of the trimethylsilyl enolate 1 promoted by tetra-n-butylam-monium fluoride. The adduct 2 was alkylated by l-bromo-2-pentyne in the presence of tetra-n-butylammonium fluoride to give 3 in rather low yield. Remaining steps to 5 were methanolysis and partial hydrogenation of the triple bond. 

Although it has been known since 1938 that alkoxy-substituted alkyl cyclopropanecar-boxylates can be opened to 1,4-dicarbonyl compounds it was not until 1970 that the synthetic merit of this route to a valuable class of intermediates was recognized. In this year Wenkert and coworkers described the preparation of cyclopentenones from this type of cyclopropane via 1,4-diketones as outlined in equation 83 " . Shortly later McMurry and Glass have published a ds-jasmone synthesis following the same principle ... 

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