Cyclopentenone synthesis oxidation

Interestingly, zirconacyclopentane 246 formed by the reaction of 1,6-heptadiene with the Zr complex has the firms ring junction mainly [108]. It should be noted that the preparation of the trans ring junction in the bicyclo[3.3.0]octane system by other means is difficult. Carbonylation of 246 affords trans-fuzed bicyclo[3.3.0]octanone 247 [109,111]. The diacetoxy compound 248 is obtained by oxidative cleavage of 246. Protonation affords the frans-dimethylcyclopentane skeleton. Similar reactions occur with 1,6-enynes, and Pauson Khand-type cyclopentenone synthesis is possible by carbonylation. 

Intramolecular hydroacylation of 4-aIkenals is a well-established method for producing cyclopentanones in which a C=C bond inserts into the Rh hydride formed by C-H oxidative addition to Rh(I) with chiral ligands and suitable alkenal substrates, useful asymmetric induction is possible. Extension to cyclopentenone synthesis requires a trans addition of Rh—H across the alkyne (see Section 7.2). ... 

A conveniently short synthesis of a1prostadi1 begins with a mixed aldol assembly of the requisite cyclopentenone 13. This product is then oxidatively cleaved with periodate-permanganate and the alcohol moiety is protected as the tetra-hydropyranyl ether (14). Aqueous chromous sulfate satisfactorily reduces the olefinic linkage and the trans stereoisomer 15 predominates after work-up. The remainder of the synthesis of involves the usual steps, through 16 to with the exception that thexyl tetrahydrolimonyllithium borohydride is used to reduce the C-15 keto moiety so as to produce preferentially the desired C-15S stereochemistry. 

Because the a-nitroketones are prepared by the acylation of nitroalkanes (see Section 5.2), by the oxidation of (3-nitro alcohols (Section 3.2.3), or by the nitration of enol acetates (Section 2.2.5), denitration of a-nitro ketones provides a useful method for the preparation of ketones (Scheme 7.10). A simple synthesis of cyclopentenone derivatives is shown in Eq. 7.66.76... 

Conversion of furfuryl alcohol derivatives 48 to pyranones 49 (Achmatowicz oxidative ring expansion) is employed in the synthesis of spiroketal moiety of a natural product and cyclopentenones <00TL6879>. 

A total synthesis of functionalized 8,14-seco steroids with five- and six-membered D rings has been developed (467). The synthesis is based on the transformation of (S)-carvone into a steroidal AB ring moiety with a side chain at C(9), which allows the creation of a nitrile oxide at this position. The nitrile oxides are coupled with cyclic enones or enol derivatives of 1,3-diketones, and reductive cleavage of the obtained cycloadducts give the desired products. The formation of a twelve-membered ring compound has been reported in the cycloaddition of one of the nitrile oxides with cyclopentenone and as the result of an intramolecular ene reaction, followed by retro-aldol reaction. 

D-Ribonolactone is a convenient source of chiral cyclopentenones, acyclic structures, and oxacyclic systems, useful intermediates for the synthesis of biologically important molecules. Cyclopentenones derived from ribono-lactone have been employed for the synthesis of prostanoids and carbocyclic nucleosides. The cyclopentenone 280 was synthesized (265) from 2,3-0-cyclohexylidene-D-ribono-1,4-lactone (16b) by a threestep synthesis that involves successive periodate oxidation, glycosylation of the lactol with 2-propanol to give 279, and treatment of 279 with lithium dimethyl methyl-phosphonate. The enantiomer of 280 was prepared from D-mannose by converting it to the corresponding lactone, which was selectively protected at HO-2, HO-3 by acetalization. Likewise, the isopropylidene derivative 282 was obtained (266) via the intermediate unsaturated lactone 281, prepared from 16a. Reduction of 281 with di-tert-butoxy lithium aluminum hydride, followed by mesylation, gave 282. 

Chalcone, chromone, flavone, /rans-cinnamaldehyde, cyclopentenone, etc. gave the corresponding products in satisfactory yields [28], The oxidation of some disub-stituted a,j8-unsaturated cyclic ketones, however, gave predominantly hydroxylated products [29], An interesting variation was the synthesis of ds-hydroxyflavanones from 2-hydroxychalcones, e.g. [30] ... 

The facile synthesis of 4,4-dimethyl-2-cyclopentenone by the allylation of isobutanal, followed by the oxidation and aldol condensation of Ae keto aldehyde is another example. ... 

It is well known that ir-allylpalladium complexes (86) are easily formed by the reaction of PdCb with P. y-unsaturated esters or ketones (85). An attempted oxidation of. y-unsaturated esters and ketones with the PdCl2/CuCl/02 catalyst system in aqueous DMF led to ir-allylpalladium complex formation as the main reaction, and the oxidation of the alkenic bond was hardly observed to a significant extent. However, in aqueous dioxane or THF, the oxidation became the main reaction, giving y-keto esters and 1,4-diketones (87), respectively, with high regioselectivity (Scheme 26).Some results are shown in Table 2. In all cases, no P-keto ester or 1,3-diketone was detected. At the end of the reaction, formation of a considerable amount of the ir-allylpalladium complex (86) was observed. y-Keto esters and 1,4-diketones are useful intermediates for Ae preparation of cyclopentanedione and cyclopentenone, respectively, by base-catalyzed cyclization. Tliis regioselective oxidation provides a unique and efficient synthetic method for y-keto ester and 1,4-diketone synthesis. 

One synthesis of cyclopentenone [80], requiring a resolution, involved initial ring contraction of phenol when treated with alkaline hypochlorite (49). Resolution of the resulting cis acid [85] was effected with brucine. The desired enantiomer [86] formed the more soluble brucine salt and was thus obtained from the mother liquors of the initial resolution. Oxidative decarboxylation with lead tetracetate, partial dechlorination with chro-mous chloride, and alcohol protection gave chloro enone [87]. Zinc-silver couple (50) dechlorinated [87] to the desired cyclopentenone [80]. 

An intriguing synthesis of chiral cyclopentenone [100] from D-glucose has recently been described (53). The readily available diacetone glucose [94] was benzylated, selectively deprotected, and oxidatively cleaved to the aldehyde, which was condensed with nitromethane to adduct [95]. Acidic hydrolysis of the product gave hemiacetal [96], cleaved with periodate in methanol to aldehyde [97], Aldol-type cyclization was effected with triethylamine subsequent dehydration to [98] was induced by mesyl-ation. The nitro olefin [98], upon treatment with activated lead in an acidic media, was converted to ketone [99], Mesylation in the presence of triethylamine then led directly to cyclopentenone [100],... 

Two asymmetric synthesis approaches to chiral cyclopentenone derivatives can be envisaged. The first, reduced to practice by Noyori (43), involved reduction of cyclopentene-l,4-dione with lithium aluminum hydride chirally modified with binaphthol to give R-4-hydroxycyclopent-2-en-l-one in 94% e.e. Alternatively, manganese dioxide oxidation of allylic alcohol [40] (Fig. 7), in analogy to the cis isomer (54), would be expected to give the same enone. 

The Homer-Wittig process has been utilized in the synthesis of vitamin D and its metabolites. Recently, a process was developed for the synthesis of hydrindanols by the 1,4-addition of the phosphine oxide to cyclopentenone. After further elaboration, the phosphine oxide formed (250) can be utilized to incorporate side chains (251 equation 58). 

D Onofrio, F., Piancatelli, G., and Nicolai, M., Photo-oxidation of 2-furylalkylphosphonalcs. Synthesis of new cyclopentenone derivatives, Tetrahedron, 51, 4083, 1995. 

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